RESEARCH III.

RELATING TO THE RESPIRATION OF NITROUS OXIDE, AND OTHER GASES.

DIVISION I.

EXPERIMENTS and OBSERVATIONS on the EFFECTS produced upon ANIMALS by the RESPIRATION of NITROUS OXIDE.

I. Preliminaries.

The term respirable, in its physiological application, has been differently employed. Some times by the respirability of a gas has been meant, its power of supporting life for a great length of time, when repeatedly applied to the blood in the lungs. At other times all gases have been considered as respirable, which were capable of introduction into the lungs by voluntary efforts, without any relation to their vitality.

In the last sense the word respirable is most properly employed. In this sense it is used in the following sections.

Non-respirable gases are those, which when applied to the external organs of respiration, stimulate the muscles of the epiglottis in inch a way as to keep it perfectly close on the glottis; thus preventing the smallest particle of gas from entering into the bronchia, in spite of voluntary exertions; such are carbonic acid, and acid gases in general.[183]

Of respirable gases, or those which are capable of being taken into the lungs by voluntary efforts.

One only has the power of uniformly supporting life;—atmospheric air. Other gases, when respired, sooner or later produce death; but in different modes.

Some, as nitrogene and hydrogene, effect no positive change in the venous blood. Animals immersed in these gases die of a disease produced by privation of atmospheric air, analogous to that occasioned by their submersion in water, or non-respirable gases.

Others, as the different varieties of hydrocarbonate, destroy life by producing some positive change[184] in the blood, which probably immediately renders it incapable of supplying the nervous and muscular fibres with principles essential to sensibility and irritability.

Oxygene, which is capable of being respired for a much greater length of time than any other gas, except common air, finally destroys life; first producing changes in the blood, connected with new living action.[185]

After experiments, to be detailed hereafter, made upon myself and others, had proved that nitrous oxide was respirable, and capable of supporting life for a longer time than any of the gases, except atmospheric air and oxygene, I was anxious to ascertain the effects of it upon animals, in cases where its action could be carried to a full extent; and to compare the changes occasioned by it in their organs, with those produced by other powers.

II. On the respiration of Nitrous Oxide by warm-blooded Animals.

The nitrous oxide employed in the following experiments, was procured from nitrate of ammoniac, and received in large jars, filled with water previously saturated with the gas. The animal was introduced into the jar, by being carried under the water; after its introduction, the jar was made to rest on a shelf, about half an inch below the surface of the water; and the animal carefully supported, so as to prevent his mouth from resting in the water.

This mode of experimenting, either under water or mercury, is absolutely necessary, to ascertain with accuracy the effects of pure gases on living beings. In some experiments that I made on the respiration of nitrous oxide, by animals that were plunged into jars of it opened in the atmosphere, and immediately closed after their introduction, the unknown quantities of common air carried in, were always sufficient to render the results perfectly inaccurate.

Animals suffer little or nothing by being passed through water.

That the phænomena in these experiments might be more accurately observed, two or three persons were always present at the time of their execution, and an account of them was noted down immediately after.

a. A stout and healthy young cat, of four or five months old, was introduced into a large jar of nitrous oxide. For ten or twelve moments he remained perfectly quiet, and then began to make violent motions, throwing himself round the jar in every direction. In two minutes he appeared quite exhausted, and sunk quietly to the bottom of the jar. On applying my hand to the thorax, I found that the heart beat with extreme violence; on feeling about the neck, I could distinctly perceive a strong and quick pulsation of the carotids. In about three minutes the animal revived, and panted very much; but still continued to lie on his side. His inspirations then became longer and deeper, and he sometimes uttered very feeble cries. In four minutes the pulsations of the heart appeared quicker and feebler. His inspirations were at long intervals, and very irregular; in five minutes the pulse was hardly perceptible; he made no motions, and appeared wholly senseless. After five minutes and quarter he was taken out, and exposed to the atmosphere before a warm fire. In a few seconds he began to move, and to take deep inspirations. In five minutes he attempted to rise on his legs; but soon fell again, the extremities being slightly convulsed. In eight or nine minutes he was able to walk, but his motions were staggering and unequal, the right leg being convulsed, whilst the other was apparently stiff and immoveable; in about half an hour he was almost completely recovered.

b. A healthy kitten, of about six weeks old, was introduced into nitrous oxide. She very soon began to make violent exertions, and in less than a minute fell to the bottom of the receiver, as if apoplectic. At this moment, applying my hand to her side, I felt the heart beating with great violence. She continued gasping, with long inspirations, for three minutes and half; at the end of five minutes and half she was taken out completely dead.

c. Another kitten of the same breed was introduced into nitrous oxide, the day after. She exhibited the same phænomena, and died in it in about five minutes and half.

d. A small dog that had accidentally met with a dislocation of the vertebræ of the loins, and was in great pain, as manifested by his moaning and whining, was introduced into a large jar of nitrous oxide. He immediately became quiet, and lay on his side in the jar, breathing very deeply. In four minutes his respiration became noisy, and his eyes sparkled very much. I was not able to apply my hand to the thorax. In five minutes he appeared senseless, and in seven minutes was perfectly dead.

e. A strong rabbit, of ten or twelve months old, was introduced into nitrous oxide. He immediately began to struggle very much, and in a minute fell down senseless: in two minutes the legs became convulsed, and his inspirations were deep and noisy: in less than five minutes he appeared perfectly dead.

f. A rabbit of a month old introduced into nitrous oxide, became senseless in less than a minute; the pulsations of the heart were very strong at this moment: they gradually became weaker, and in three minutes and half the animal was dead.

g. Another rabbit of the same breed, after being rendered senseless in nitrous oxide in a minute and half, was taken out. He soon became convulsed; in a minute began to breathe quickly; in two minutes attempted to rise, but staggered, and fell again on his side. His hinder legs were paralytic for near five minutes. In twenty he had almost recovered.

h. A middle sized guinea-pig was much convulsed, after being in nitrous oxide for a minute. In two minutes and half he was senseless. Taken out at this period, he remained for some minutes by the side of a warm fire, without moving; his fore legs then became convulsed; his hind legs were perfectly paralytic. In this state he continued, without attempting to rise or move, for near an hour, when he died.

i. A large and old guinea-pig died in nitrous oxide, exhibiting the same phænomena as the other animals, in about five minutes and quarter. A young one was killed in three minutes and half.

j. A small guinea-pig, after breathing nitrous oxide for a minute and half, was taken out, and placed before a warm fire. He was for a few minutes a little convulsed; but in a quarter of an hour got quite well, and did not relapse.

k. A large mouse introduced into nitrous oxide, was for a few seconds very active. In half a minute he fell down senseless; in a minute and quarter he appeared perfectly dead.

l. A mouse taken out of nitrous oxide, after being in it for half a minute, continued convulsed for some minutes, but finally recovered.

m. A young hen was introduced into a vessel filled with nitrous oxide. She immediately began to struggle very much; fell on her breast in less than half a minute, and in two minutes was quite dead.

n. A goldfinch died in nitrous oxide in less than a minute.

In each of these experiments a certain absorption of the gas was always perceived, the water rising in the jar during the respiration of the animal. From them we learn

1st. That nitrous oxide is destructive when respired for a certain time to the warm-blooded animals, apparently previously exciting them to a great extent.

2dly. That when its operation is stopped before compleat exhaustion is brought on, the healthy living action is capable of being gradually reproduced, by enabling the animal to respire atmospheric air.

3dly. That exhaustion and death is produced in the small animals by nitrous oxide sooner than in the larger ones, and in young animals of the same species, in a shorter time than in old ones, as indeed Dr. Beddoes had conjectured a priori would be the case.

Most of the animals destroyed in these experiments were examined after death; the appearances in their organs were peculiar. To prevent unnecessary repetitions, an account of them will be given in the fourth section.

III. Effects of the respiration of Nitrous Oxide upon animals, as compared with those produced by their immersion in Hydrogene and Water.

Before the following experiments were made, a number of circumstances had convinced me that nitrous oxide acted on animals by producing some positive change in their blood, connected with new living action of the irritable and sensitive organs, and terminating in their death.

To ascertain however, the difference between the effects of this gas and those of hydrogene and non-respirable gases, I proceeded in the following way.

a. Of two healthy rabbits of about two months old, of the same breed, and nearly of the same size.

One was introduced into nitrous oxide. In a half a minute, it had fallen down apparently senseless. On applying my hand to the thorax, the action of the heart appeared at first, very quick and strong, it gradually became weaker, and in two minutes and half, the animal was taken out quite dead.

The other was introduced into a jar of pure hydrogene through water. He immediately began to struggle very much, and in a quarter of a minute fell on his side. On feeling the thorax, the pulsations of the heart appeared very quick and feeble, they gradually diminished; his breathing became momentarily shorter, and in rather more than three quarters of a minute, he was taken out dead. Dr. Kinglake was present at this experiment, and afterwards dissected both of the animals.

b. Of two similar rabbits of the same breed, nearly three months old. One was introduced into nitrous oxide, and after being rendered senseless by the respiration of it for nearly a minute and half, was exposed to the atmosphere, before a warm fire. He recovered gradually, but was occasionally convulsed, and had a paralysis of one of his hinder legs for some minutes: in an hour he was able to walk. The other, after being immerged in hydrogene for near half a minute, was restored to the atmosphere apparently inanimate. In less than a minute he began to breathe, and to utter a feeble noise; in two minutes was able to walk, and in less than three minutes appeared perfectly recovered.

c. A kitten of about two months old, was introduced into a jar of nitrous oxide, at the same time that another of the same breed was plunged under a jar of water. They both struggled very much. The animal in the nitrous oxide fell senseless before that under water had ceased to struggle, and to throw out air from its lungs. In two minutes and three quarters, the animal under water was quite dead: it was taken out and exposed to heat and air, but did not shew the slightest signs of life. At the end of three minutes and half, the animal in nitrous oxide began to gasp, breathing very slowly; at four minutes and three quarters it was yet alive; at the end of five minutes and quarter it appeared perfectly dead. It was taken out, and did not recover.

From these experiments it was evident, that animals lived at least twice as long in nitrous oxide as in hydrogene or water. Consequently from this circumstance alone, there was every reason to suppose that their death in nitrous oxide could not depend on the simple privation of atmospheric air; but that it was owing to some peculiar changes effected in the blood by the gas.

IV. Of the changes effected in the Organisation of warm-blooded Animals, by the respiration of Nitrous Oxide.

The external appearance of animals that have been destroyed in nitrous oxide, is very little different from that of those killed by privation of atmospheric air. The fauces and tongue appear of a dark red, and the eyes are dull, and a little protruded. Their internal organs, however, exhibit a very peculiar change. The lungs are pale brown red, and covered here and there with purple spots; the liver is of a very bright red, and the muscular fibre in general dark. Both the auricles and ventricles of the heart are filled with blood. The auricles contract for minutes after the death of the animal. The blood in the left ventricle, and the aorta, is of a tinge between purple and red, whilst that in the right ventricle is of a dark color, rather more purple than the venous blood. But these appearances, and their causes, will be better understood after the following comparative observations are read.

a. Of two similar rabbits, about eight months old, one A, was killed by exposure for near six minutes to nitrous oxide, the other, B, was destroyed by a blow on the head.

They were both opened as speedily as possible. The lungs of B were pale, and uniform in their appearance; this organ in A was redder, and every where marked with purple spots. The liver of A was of a dark and bright red, that of B of a pale red brown. The diaphragm of B, when cut, was strongly irritable; that of A rather darker, and scarce at all contractile. All the cavities of the heart contracted for more than 50 minutes in B. The auricles contracted for near 25 minutes with force and velocity in A: but the ventricles were almost inactive. The vena cava, and the right auricle, in A, were filled with blood, apparently a shade darker than in B. The blood in the left auricle, and the aorta, appeared in A of a purple, a shade brighter than that of the venous blood. In the left auricle of B it was red.

I opened the head of each, but not without injuring the brains, so that I was unable to make any accurate comparison. The color of the brain in A appeared rather darker than in B.

b. Two rabbits, C and D, were destroyed, C by immersion in nitrous oxide, D in hydrogene: they were both dissected by Dr. Kinglake. The blood in the pulmonary vein and the left auricle of C was of a different tinge, from that in D more inclined to purple red. The membrane of the lungs in C was covered with purple spots, that of D was pale and uniform in its appearance. The brain in C was rather darker than in D; but there was no perceptible effusion of blood into the ventricles either in D or C. The liver in C was of a brighter red than in health, that in D rather paler.

c. In the last experiment, the comparative irritability of the ventricles and auricles of the heart and the muscular fibre in the two animals, had not been examined. That these circumstances might be noticed, two rabbits, E and F were killed; E under water in about a minute, and F in nitrous oxide in three minutes. They were immediately opened, and after a minute, the appearance of the heart, and organs of respiration observed.

Both the right and left ventricles of the heart in F contracted but very feebly; the auricles regularly and quickly contracted; the aorta appeared perfectly full of blood. In E, a feeble contraction of the left sinus venosus and auricle was observed; the left ventricle did not contract: the right contracted, but more slowly than in F. In a few minutes, the contractions of the ventricles in F had ceased, whilst the auricles contracted as strongly and quickly as before. The blood in the pulmonary veins of F was rather of a redder purple than in E; the difference of the blood in the vena cava was hardly perceptible, perhaps it was a little more purple in F. The membranous substance of the lungs in F was spotted with purple as from extravasated blood, whilst that in E was pale. The brain in F was darker than in E. On opening the ventricles no extravasation of blood was perceptible. The auricles of the heart in F contracted strongly for near twenty minutes, and then gradually their motion became less frequent; in twenty-eight minutes it had wholly ceased. The right auricle and ventricle in E, occasionally contracted for half an hour. The livers of both animals were similar when they were first opened, of a dark red; that of F preserved its color for some time when exposed to the atmosphere; whilst that of E almost immediately became paler under the same circumstances.

The peristaltic motion continued for nearly an equal time in both animals.

d. The sternum of a young rabbit was removed so that the heart and lungs could be perceived, and he was introduced into a vessel filled with nitrous oxide; the blood in the pulmonary veins gradually became more purple, and the heart appeared to beat quicker than before, all the muscles contracting with great force. After he had been in about a minute, spots began to appear on the lungs, though the contractions of the heart became quicker and weaker; in three minutes and half he was quite dead; after death the ventricles contracted very feebly, though the contractions of the auricles were as strong almost after the end of five minutes as at first. This animal was passed through water saturated with nitrous oxide; possibly this fluid had some effect on his organs.

Besides these animals, many others, as guinea-pigs, mice and birds, were dissected after being destroyed in nitrous oxide; in all of them the same general appearance was observed. Their muscular fibre almost always appeared less irritable than that of animals destroyed, by organic læsion of part of the nervous system, in the atmosphere. The ventricles of the heart in general, contracted feebly and for a very short time; whilst the auricles continued to act for a great length of time. The lungs were dark in their appearance, and always suffused here and there with purple; the blood in the pulmonary veins when slightly observed, appeared dark, like venous blood, but when minutely examined, was evidently much more purple. The blood in the vena cava, was darker than that in the pulmonary veins. The cerebrum was dark.

In a late experiment, I thought I perceived a slight extravasation of blood in one of the ventricles of the brain in a rabbit destroyed in nitrous oxide; but as this appearance had not occurred in the animals I had examined before, or in those dissected by Dr. Kinglake, and Mr. King, Surgeon, I am inclined to refer it to an accidental cause. At my request, Mr. Smith, Surgeon, examined the brain of a young rabbit that had been killed in his presence in nitrous oxide; he was of opinion that no effusion of blood into the ventricles had taken place.

In comparing the external appearance of the crural nerves in two rabbits that had been dissected by Dr. Kinglake, having been destroyed one in hydrogene, the other in nitrous oxide, we could perceive no perceptible difference.

It deserves to be noticed, that whenever the gall bladder and the urinary bladder have been examined in animals destroyed in nitrous oxide, they have been always distended with fluid; which is hardly ever the case in animals killed by privation of atmospheric air.

In the infancy of my experiments on the action of nitrous oxide upon animals, I thought that it rendered the venous blood less coagulable; but this I now find to be a mistake. The blood from the pulmonary veins of animals killed in nitrous oxide, does not sensibly differ in this respect from the arterial blood of those destroyed in hydrogene, and both become vermilion nearly in the same time when exposed to the atmosphere.

In describing the various shades of color of the blood in the preceding observations on the different dissected animals, the poverty of the language of color, has obliged me to adopt terms, which I fear will hardly convey to the mind of the reader, distinct notions of the differences observable by minute examination in the venous and arterial blood of animals that die of privation of atmospheric air, and of those destroyed by the action of nitrous oxide. This difference can only be observed in the vessels by means of a strong light; it may however be easily noticed in the fluid blood by the introduction of it from the arteries or veins at the moment of their incision, between two polished surfaces of white glass,[186] so closely adapted to each other, as to prevent the blood from coming in contact with the atmosphere.

Having four or five times had an opportunity of bleeding people in the arm for trifling complaints, I have always received the blood in phials, filled with various gases, in a mode to be described hereafter. Venous blood agitated in nitrous oxide, compared with similar blood in common air, hydrogene, and nitrogene, was always darker and more purple than the first, and much brighter and more florid than the two last, which were not different in their color from venous blood, received between two surfaces of glass. It will be seen hereafter, that the coagulum of venous blood is rendered more purple when exposed to nitrous oxide, whilst the gas is absorbed; likewise that blood altered by nitrous oxide, is capable of being again rendered vermilion, by exposure to the air.

The appearances noticed in the above mentioned experiments, in the lungs of animals destroyed in nitrous oxide, are similar to those observed by Dr. Beddoes, in animals that had been made to breathe oxygene for a great length of time.

There were many reasons for supposing that the large purple spots in the lungs of animals destroyed in nitrous oxide, were owing to extravasation of venous blood from the capillary vessels; their coats being broken by the highly increased arterial action. To ascertain whether these phænomena existed at a period of the action of nitrous oxide, when the animal was recoverable by exposure to the atmosphere.

I introduced a rabbit of six months old, into a vessel of nitrous oxide, and after a minute, when it had fallen down apparently apoplectic, plunged him wholly under water; he immediately began to struggle, and what surprised me very much, died in less than a minute after submersion. On opening the thorax, the blood in the pulmonary veins was nearly of the color of that in animals that have been simply drowned. The lungs were here and there, marked with a few points; but there were no large purple spots, as in animals that have been wholly destroyed in nitrous oxide: the right side of the heart only contracted. In this experiment, the excitement from the action of the gas was probably carried to such an extent, as to produce indirect debility. There are reasons for supposing, that animals after having been excited to but a small extent by the respiration of nitrous oxide, will live under water for a greater length of time, than animals previously made to breathe common air.

V. Of the respiration of mixtures of Nitrous Oxide, and other gases, by warm-blooded Animals.

a. A rabbit of near two months old, was introduced into a mixture of equal parts hydrogene and nitrous oxide through water. He immediately began to struggle; in a minute fell on his side; in three minutes gasped, and made long inspirations; and in four minutes and half, was dead. On dissection, he exhibited the same appearances as animals destroyed in nitrous oxide.

b. A large and strong mouse was introduced into a mixture of three parts hydrogene to one part nitrous oxide. He immediately began to struggle very much, in half a minute, became convulsed, and in about a minute, was quite dead.

c. Into a mixture of one oxygene, and three nitrous oxide, a small guinea-pig was introduced. He immediately began to struggle, and in two minutes reposed on his side, breathing very deeply. He made afterwards no violent muscular motion; but lived quietly for near fourteen minutes: at the end of which time, his legs were much convulsed. He was taken out, and recovered.

d. A mouse lived apparently without suffering, for near ten minutes, in a mixture of 1 atmospheric air, and 3 nitrous oxide, at the end of eleven minutes he began to struggle, and in thirteen minutes became much convulsed.

e. A cat of three months old, lived for seventeen minutes, in a very large quantity of a mixture of 1 atmospheric air, and 12 nitrous oxide. On her first introduction she was very much agitated and convulsed, in a minute and half she fell down as if apoplectic, and continued breathing very deeply during the remainder of the time, sometimes uttering very feeble cries. When taken out, she appeared almost inanimate, but on being laid before the fire, gradually began to breathe and move; being for some time, like most of the animals that have recovered after breathing nitrous oxide, convulsed on one side, and paralytic the other.

f. A goldfinch lived for near five minutes in a mixture of equal parts nitrous oxide and oxygene, without apparently suffering. Taken out, he appeared faint and languid, but finally recovered.[187]

VI. Recapitulation of facts relating to the respiration of Nitrous Oxide, by warm-blooded Animals.

1. Warm-blooded animals die in nitrous oxide infinitely sooner than in common air or oxygene; but not nearly in so short a time as in gases incapable of effecting positive changes in the venous blood, or in non-respirable gases.

2. The larger animals live longer in nitrous oxide than the smaller ones, and young animals die in it sooner than old ones of the same species.

3. When animals, after breathing nitrous oxide, are removed from it before compleat exhaustion has taken place, they are capable of being restored to health under the action of atmospheric air.

4. Peculiar changes are effected in the organs of animals by the respiration of nitrous oxide. In animals destroyed by it, the arterial blood is purple red, the lungs are covered with purple spots, both the hollow and compact muscles are apparently very inirritable, and the brain is dark colored.

5. Animals are destroyed by the respiration of mixtures of nitrous oxide and hydrogene nearly in the same time as by pure nitrous oxide; they are capable of living for a great length of time in nitrous oxide mingled with very minute quantities of oxygene or common air.

These facts will be reasoned upon in the next division.

VII. Of the respiration of Nitrous Oxide by amphibious Animals.

As from the foregoing experiments, it appeared that the nitrous oxide destroyed warm-blooded animals by increasing the living action of their organs to such an extent, as finally to exhaust their irritability and sensibility; it was reasonable to conjecture that the cold-blooded animals, possessed of voluntary power over respiration, would so regulate the quantity of nitrous oxide applied to the blood in their lungs as to bear its action for a great length of time. This conjecture was put to the test of experiment; the following facts will prove its error.

a. Of two middle sized water-lizards, one was introduced into a small jar filled with nitrous oxide, over moist mercury, by being passed through the mercury; the other was made to breathe hydrogene, by being carried into it in the same manner.

The lizard in nitrous oxide, in two or three minutes, began to make violent motions, appeared very uneasy, and rolled about the jar in every direction, sometimes attempting to climb to the top of it. The animal in hydrogene was all this time very quiet, and crawled about the vessel without being apparently much affected. At the end of twelve minutes, the lizard in nitrous oxide was lying on his back seemingly dead; but on agitating the jar he moved a little; at the end of fifteen minutes he did not move on agitation, and his paws were resting on his belly. He was now taken out stiff and apparently lifeless, but after being exposed to the atmosphere for three or four minutes, took an inspiration, and moved his head a little; he then raised the end of his tail, though the middle of it was still stiff and did not bend when touched. His four legs remained close to his side, and were apparently useless; but on pricking them with the point of a lancet, they became convulsed. After being introduced into shallow water, he was able to crawl in a quarter of an hour, though his motions were very irregular. In an hour he was quite well. The animal in hydrogene appeared to have suffered very little in three quarters of an hour, and had raised himself against the side of the jar. At the end of an hour he was taken out, and very soon recovered.

b. Some hours after, the same lizards were again experimented upon. That which had been inserted into hydrogene in the last experiment, being now inserted into nitrous oxide.

This lizard was apparently lifeless in fourteen minutes, having tumbled and writhed himself very much during the first ten minutes. Taken out after being in twenty-five minutes, he did not recover. The other lizard lived in hydrogene for near an hour and quarter, taken out after an hour and twenty minutes, he was dead.

These animals were both opened, but the viscera of the nitrous oxide lizard were so much injured by the knife, that no accurate comparison of them with those of the other could be made, I thought that the lungs appeared rather redder.

c. Of two similar large water-lizards, one was introduced into a vessel standing over mercury, wholly filled with water that had been long boiled and suffered to cool under mercury.

The animal very often rose to the top of the jar as, if in search of air, during the first half hour; but shewed no other signs of uneasiness. At the end of three quarters of an hour, he became very weak, and appeared scarcely able to swim in the water. Taken out at the end of fifty minutes, he recovered.

The other was inserted into nitrous oxide. After much struggling, he became senseless in about fifteen minutes, and lay on his back. Taken out at the end of twenty minutes, he remained for a long time motionless and stiff, but in a quarter of an hour, began to move some of his limbs.

From these experiments, we may conclude, that water-lizards, and most probably the other amphibious animals, die in nitrous oxide in a much shorter time than in hydrogene or pure water; consequently their death in it cannot depend on the simple privation of atmospheric air.

At the season of the year in which this investigation was carried on, I was unable to procure frogs or toads. This I regret very much.

Supposing that cold-blooded animals die in nitrous oxide from positive changes effected in their blood by the gas, it would be extremely interesting to notice the apparent alterations taking place in their organs of respiration and circulation during its action, which could easily be done, the membranous substance of their lungs being transparent. The increase or diminution of the irritability of their muscular fibre, might be determined by comparative galvanic experiments.

VIII. Effects of solution of nitrous oxide in water on Fishes.

a. A small flounder was introduced into a vessel filled with solution of nitrous oxide in water over mercury. He remained at rest for ten minutes and then began to move about the jar in different directions. In a half an hour he was apparently dying, lying on his side in the water. He was now taken out, and introduced into a vessel filled with water saturated with common air, he very soon recovered.

b. Of two large thornbacks,[188] equally brisk and lively. One, A, was introduced into a jar containing nearly 3 cubic inches of water, saturated with nitrous oxide, and which previous to its impregnation had been long boiled; the other, B, was introduced into an equal quantity of water which had been deprived of air by distillation through mercury.

A, appeared very quiet for two or three minutes, and then began to move up and down in the jar, as if agitated. In eight minutes his motions became very irregular, and he darted obliquely from one side of the jar to the other. In twelve minutes, he became still, and moved his gills very slowly. In fifteen minutes he appeared dead. After sixteen minutes he was taken out, but shewed no signs of life.

B was very quiet for four minutes and half. He then began to move about the jar. In seven minutes he had fallen on his back, but still continued to move his gills. In eleven minutes he was motionless; taken out after thirteen minutes, he did not recover.

c. Of two thornbacks, one, C was introduced into about an ounce of boiled water in contact with hydrogene, standing over mercury. The other, D, was introduced into well boiled water saturated with nitrous oxide, and standing in contact with it over mercury. C lived near thirteen minutes, and died without being previously much agitated. D was apparently motionless, after having the same affections as A in the last experiment, in sixteen minutes. At the end of this time he was taken out and introduced into common water. He soon began to move his gills, and in less than a quarter of an hour was so far recovered as to be able to swim.

The last experiment was repeated on two smaller thornbacks; that in the aqueous solution of nitrous oxide lived near seventeen minutes, that in the water in contact with hydrogene, about fifteen and half.

The experiments in Res. I. Div. 3, prove the difficulty, and indeed almost impossibility of driving from water by boiling, the whole of the atmospheric air held in solution by it; they likewise show that nitrous oxide by its strong affinity for water, is capable of expelling air from that fluid after no more can be procured from it by ebullition.

Hence, if water saturated with nitrous oxide had no positive effects upon fishes; they ought to die in it much sooner than in water deprived of air by ebullition. From their living in it rather longer;[189] we may conclude, that they are destroyed not by privation of atmospheric air, but from some positive change effected in their blood by the gas.

A long while ago, from observing that the gills of fish became rather of a lighter red during their death, in the atmosphere; I conjectured that the disease of which they died, was probably hyperoxygenation of the blood connected with highly increased animal heat. For not only is oxygene presented to their blood in much larger quantities in atmospheric air than in its aqueous solution; but likewise, to use common language, in a state in which it contains much more latent heat. Without however laying any stress on this supposition, I had the curiosity to try whether thornbacks would live longest in atmospheric air or nitrous oxide. In one experiment, they appeared to die in them nearly in the same time. In another, the fish in nitrous oxide lived nearly half as long again as that in atmospheric air.

IX. Effects of Nitrous Oxide on Insects.

The winged insects furnished with breathing holes, become motionless in nitrous oxide very speedily; being however possessed of a certain voluntary power over respiration, they sometimes recover, after having been exposed to it for some minutes, under the action of atmospheric air.

A butterfly was introduced into a small jar, filled with pure nitrous oxide, over mercury, He struggled a little during the first two or three seconds; in about seven seconds, his legs became convulsed, and his wings were wrapt round his body; in about half a minute he was senseless; taken out after six minutes, he did not recover.

Another butterfly introduced into hydrogene, became convulsed in about a quarter of a minute, was senseless in twenty seconds, and taken out after five minutes, did not revive.

A large drone, after being in nitrous oxide for a minute and a quarter, was taken out senseless. After being for some time exposed to the atmosphere, he began to move, and at last rose on his wings. For some time, however, he was unable to fly in a straight line; and often after describing circles in the air, fell to the ground as if giddy.

A large fly, became motionless in nitrous oxide after being convulsed, in about half a minute. Another was rendered senseless in hydrogene, in less than a quarter of a minute.

A fly introduced into hydrocarbonate, dropt immediately senseless; taken out after about a quarter of a minute, he recovered; but like the fly that had lived after exposure to nitrous oxide, was for some time vertiginous.

Flies live much longer under water, alcohol, or oil, than in non-respirable gases, or gases incapable of supporting life. A certain quantity of air always continues attached in the fluid to the fine hairs surrounding their breathing holes, sufficient to support life for a short time.

Snails and earth-worms, live in nitrous oxide a long while, they die in it however, much sooner than in water or hydrogene; probably from the same causes as the amphibious animals.

DIVISION II.

Of the CHANGES effected in NITROUS OXIDE, and other GASES, by the RESPIRATION of ANIMALS.

I. Preliminaries.

As soon as I had discovered that nitrous oxide was respirable, and possessed of extraordinary powers of action on living beings, I was anxious to be acquainted with the changes effected in it by the venous blood. To investigate these changes, appeared at first a simple problem; I soon however found that it involved much preliminary knowledge of the chemical properties and affinities of nitrous oxide. After I had ascertained by experiments detailed in the preceding Researches, the composition of this gas its combinations, and the physical changes effected by it in living beings, I began my enquiry relating to the mode of its operation.

Finding that the residual gas of nitrous oxide after it had been breathed for some time in silk bags, was chiefly nitrogene, I at first conjectured that nitrous oxide was decomposed in respiration in the same manner as atmospheric air, and its oxygene only combined with the venous blood; the following experiments soon however convinced me of my error.

II. Absorption of Nitrous Oxide by venous blood. Changes effected in the blood by different Gases.

a. Though the laws of the coagulability of the blood are unknown, yet we are certain that at the moment of coagulation, a perfectly new arrangement of its principles takes place; consequently, their powers of combination must be newly modified. The affinities of living blood can only be ascertained during its circulation in the vessels of animals. At the moment of effusion from those vessels, it begins to pass through a series of changes, which first produce coagulation, and finally its compleat decomposition.

Consequently, the action of fluid blood upon gates out of the vessels, will be more analogous to that of circulating blood in proportion as it is more speedily placed in contact with them.

b. To ascertain the changes effected in nitrous oxide by fluid venous blood.

A jar, six inches long and half an inch wide, graduated to,05 cubic inches, having a tight stopper adapted to it, was filled with nitrogene, which is a gas incapable of combining with, and possessing no power of a action upon venous blood. A large orifice was made in the vein of a tolerably healthy man, and the stopper removed from the jar, which was brought in contact with the arm so as to receive the blood, and pressed close against the skin, in such a way as to leave an orifice just sufficient for the escape of the nitrogene, as the blood flowed in. When the jar was full, it was closed, and carried to the pneumatic apparatus, the mercury of which had been previously a little warmed. A small quantity of the blood was transferred into another jar to make room for the gas. The remaining quantity equalled exactly two cubic inches; to this was introduced as speedily as possible, eleven measures equal to,55 cubic inches of nitrous oxide, which left a residuum of ¹/₃₂ only, when absorbed by boiled water, and was consequently, perfectly pure. On agitation, a rapid diminution of the gas took place.

In the mass of blood which was opaque, but little change of color could be perceived; but that portion of it diffused over the sides of the jar, was evidently of a brighter purple than the venous blood.

It was agitated for two or three minutes, and then suffered to rest; in eight minutes it had wholly coagulated; a small quantity of serum had separated, and was diffused over the coagulum. This coagulum was dark; but evidently of a more purple tinge than that of venous blood; no gas had apparently been liberated during its formation.

The nitrous oxide remaining, was not quite equal to seven measures; hence, at least four measures of it had been absorbed.

To ascertain the nature of the residuum, it was necessary to transfer it into another vessel, but this I found very difficult to accomplish, on account of the coagulated blood. By piercing through the coagulum and removing part of it by means of curved iron forceps, I at last contrived to introduce about 4½ measures of the gas into a small cylinder, graduated to,25 cubic inches, in which it occupied of course, nearly 9 measures; when a little solution of strontian was admitted to these, it became very slightly clouded; but the absorption that took place did not more than equal half its bulk. Consequently, the quantity of carbonic acid evolved from the blood, or formed, must have been extremely minute.

On the introduction of pure water, a rapid absorption of the gas took place, and after agitation, not quite 3 measures remained. These did not perceptibly diminish with nitrous gas; their quantity was too small to be examined by any other test; but there is reason to suppose that they were chiefly composed of nitrogene.

From this experiment, it appeared that nitrous oxide is absorbed when placed in contact with venous blood; at the same time, that a very minute quantity of carbonic acid and probably nitrogene is produced.

c. In another similar experiment when nearly half a cubic inch of nitrous oxide was absorbed by about a cubic inch and three quarters of fluid blood, the residual gas did not equal more than ⅛, the quantity absorbed being taken as unity. This fact induced me to suppose that the absorption of nitrous oxide by venous blood, was owing to a simple solution of the gas in that fluid, analogous to its solution in water or alcohol.

To ascertain if nitrous oxide could be expelled from blood impregnated with it, by heat; I introduced to 2 cubic inches of fluid blood taken from the medial vein, about,6 cubic inches of nitrous oxide. After agitation, in seven minutes nearly,4 were absorbed. In ten minutes, after the blood had completely coagulated, the cylinder containing it, was transferred in contact with mercury, into a vessel of solution of salt in water; this solution was heated and made to boil. During its ebullition, the whole of the blood became either white or pale brown, and formed a solid coherent mass; whilst small globules of gas were given out from it. In a few minutes, about,25 of gas had collected. After the vessel had cooled, I attempted to transfer this gas into a small graduated jar in the mercurial apparatus, but in vain; the mass in the jar was so solid and tough, that I could not remove it. By transferring it to the water apparatus, I succeeded in displacing enough of the coagulum to suffer the water to come in contact with the gas; an absorption of nearly half of it took place; hence, I conjecture, that nitrous oxide had been given out by the impregnated blood.

d. Some fresh dark coagulum of venous blood, was exposed to nitrous oxide. A very slight alteration of color took place at the surface of the blood, perceptible only in a strong light, and a minute quantity of gas was absorbed. A taper burnt in the remaining gas as brilliantly as before, hence, it had apparently suffered no alteration.

e. To compare the physical changes effected in the venous blood by nitrous oxide, with those produced by other gases, I made the following experiments.—I filled a large phial, containing near 14 cubic inches, with blood from the vein of the arm of a man, and immediately transferred it to the mercurial apparatus. Different portions of it were thrown into small graduated cylinders, filled with the following gases: nitrogene, nitrous gas, common air, oxygene, nitrous oxide, carbonic acid, and hydrocarbonate.

The blood in each of them was successively agitated till it began to coagulate; and making allowances for the different periods of agitation, there was no marked difference in the times of coagulation.

The color of the coagulum in every part of the cylinder, containing nitrogene, was the same very dark red. When it was agitated so as to tinge the sides of the jar, it appeared exactly of the color of venous blood received between two surfaces of glass; no perceptible absorption of the gas had taken place.

The blood in nitrous gas was dark, and much more purple on the top than that in nitrogene. When agitated so as to adhere to the jar as a thin surface, this purple was evidently deep and bright. An absorption of rather more than ⅛ of the volume of gas had taken place.

The blood in oxygene and atmospheric air, were of a much brighter tinge than that in any of the other gases. On the top, the color was vermilion, but no perceptible absorption had taken place.

The coagulum in nitrous oxide, when examined in the mass was dark, and hardly distinguishable in its color from venous blood; but when minutely noticed at the surface where it was covered with serum, and in its diffusion over the sides of the jar, it appeared of a fine purple red, a tinge brighter than the blood in nitrous gas. An absorption had taken place in this cylinder, more considerable than in any of the others.

In carbonic acid, the coagulum was of a brown red, much darker than the venous blood, and a slight diminution of gas had taken place.

In the hydrocarbonate,[190] the blood was red, a shade darker than the oxygenated blood, and a very slight diminution of the gas[191] was perceptible.

f. To human blood that had been saturated with nitrous oxide whilst warm and constantly agitated for four or five minutes, to prevent its uniform coagulation, oxygene was introduced; the red purple on the surface of it, immediately changed to vermilion; and on agitation, this color was diffused through it. On comparing the tinge with that of oxygenated blood, no perceptible difference could be observed. No change of volume of the oxygene introduced, had taken place; and consequently, no nitrous oxide had been evolved from the blood.

g. Blood, impregnated with nitrous gas, was exposed to oxygene; but after agitation in it for many minutes, no change of its dark purple tinge could be observed, though a slight diminution of the oxygene appeared to take place.

h. Blood that had been rendered vermilion in every part by long agitation in atmospheric air, the coagulum of which was broken and diffused with the coagulable lymph through the serum, was exposed to nitrous oxide; for some minutes no perceptible change of color took place; but by agitation for two or three hours, it evidently affirmed a purple tinge, whilst a a slight absorption of gas took place. It never however, became nearly so dark as venous blood that had been exposed to nitrous oxide.

i. Blood, oxygenated in the same manner as in the last experiment, the coagulum of which had been broken, was exposed to nitrous gas. The surface of it immediately became purple, and by agitation for a few minutes, this color was diffused through it. A slight diminution of the gas was observed. On comparing the tinge with that of venous blood that had been previously exposed to nitrous gas, there was no perceptible difference.

k. Blood exposed to oxygenated muriatic acid is wholly altered in its constitution and physical properties, as has been often noticed; the coagulum becomes black in some parts, and brown and white in others. Venous blood, after agitation in hydrogene or nitrogene, oxygenates when exposed to the atmosphere in the same manner as simple venous blood. I had the curiosity to try whether venous blood exposed to hydrogene, would retain its power of being oxygenated longer than blood saturated with nitrous oxide: for this purpose some similar black coagulum was agitated for some time in two phials, one filled with hydrogene, the other with nitrous oxide. They were then suffered to rest for three days at a temperature from about 56° to 63°. After being opened, no offensive smell was perceived in either of them, the blood in hydrogene was rather darker than at the time of their exposure, whilst that in nitrous oxide was of a brighter purple. On being agitated for some time in the atmosphere, the blood in nitrous oxide became red, but not of so bright a tinge as oxygenated venous blood. The color of the blood in hydrogene did not at all alter.

l. To ascertain whether impregnation with nitrous oxide accelerated or retarded the putrefaction of the blood; I exposed venous blood in four phials, the first filled with hydrocarbonate, the second with hydrogene; the third with atmospheric air, and the fourth with nitrous oxide. Examined after a fortnight, the blood in hydrogene and common air were both black, and stunk very much; that in hydrocarbonate was red, and perfectly sweet; that in nitrous oxide appeared purple and had no disagreeable smell.

In a second experiment, when blood was exposed for three weeks to hydrocarbonate and nitrous oxide, that in nitrous oxide was darker than before and stunk a little; that in hydrocarbonate was still perfectly sweet. The power of hydrocarbonate to prevent the putrefaction of animal matters, was long ago noticed by Mr. Watt.

m. Having accidentally cut one of my fingers so as to lay bare a little muscular fibre, I introduced it whilst bleeding into a bottle of nitrous oxide; the blood that trickled from the wound evidently became much more purple; but the pain was neither alleviated or increased. When however, the finger was taken out of the nitrous oxide and exposed to the atmosphere, the wound smarted more than it had done before. After it had ceased to bleed, I inserted it through water into a vessel of nitrous gas; but it did not become more painful than before.

From all these observations, we may conclude,

1st. That when nitrous oxide is agitated in fluid venous blood, a certain portion of the gas is absorbed; whilst the color of the blood changes from dark red to red purple.

2dly. That during the absorption of nitrous oxide by the venous blood, minute portions of nitrogene and carbonic acid are produced, either by evolution from the blood, or from a decomposition of part of the nitrous oxide.

3dly. That venous blood impregnated with nitrous oxide is capable of oxygenation; and vice versa; that oxygenated blood may be combined with nitrous oxide.

When blood separated into coagulum and serum, is exposed to nitrous oxide, it is most probable that the gas is chiefly absorbed by the serum. That nitrous oxide however is capable of acting upon the coagulum, is evident from d. In the fluid blood, as we shall see hereafter, nitrous oxide is absorbed by the attractions of the whole compound.

III. Of the changes effected in Nitrous Oxide by Respiration.

To ascertain whether the changes effected in nitrous oxide by the circulating blood acting through the moist coats of the pulmonary veins of living animals, were highly analogous to those produced in it by fluid venous blood removed from the vessels, I found extremely difficult.

I have before observed, that when animals are made to respire nitrous oxide, a certain absorption of the gas always takes place; but the smaller animals, the only ones that can be experimented upon in the mercurial apparatus, die in nitrous oxide so speedily and occasion so slight a diminution of gas, that I judged it useless to attempt to analise the residuum of their respiration, which supports flame as well as pure nitrous oxide, and is chiefly absorbable by water.

In the infancy of my researches, I often respired nitrous oxide in a large glass bell, furnished with a breathing tube and stop-cock, and poised in water saturated with the gas.

In two or three experiments in which the nostrils being closed after the exhaustion of the lungs, the gas was inspired from the bell and respired into it, a considerable diminution was perceived, and by the test of lime water some carbonic acid appeared to have been formed; but on account of the absorption of this carbonic acid by the impregnated water, and the liberation of nitrous oxide from it, it was impossible to determine with the least accuracy, the quantities of products after respiration.

About this time likewise, I often examined the residuum of nitrous oxide, after it had been respired in silk bags. In these experiments when the gas had been breathed for a long time, a considerable diminution of it was observed, and the remainder extinguished flame and gave a very slight diminution with nitrous gas. But the great quantity of this remainder as well as other phænomena, convinced me that though the oiled silk was apparently air-tight when dry, under slight pressure, yet during the action of respiration, the moist and warm gas expired, penetrated through it, whilst common air entered through the wetted surface.

To ascertain accurately, the changes effected in nitrous oxide by respiration, I was obliged to make use of the large mercurial airholder mentioned in Research I. of the capacity of 200 cubic inches. The upper cylinder of it was accurately balanced so as to be constantly under the pressure of the atmosphere. To an aperture in it, a stop-cock having a very large orifice was adapted, curved and flattened at its upper extremity, so as to form an air-tight mouth-piece.

By accurately closing the nose, and bringing the lips tight on the mouth-piece, after a few trials I was able to breathe oxygene or common air in this machine for two minutes or two minutes and half, without any other uneasy feeling than that produced by the inclination of the neck and chest towards the cylinder. The power of uniformly exhausting the lungs and fauces to the same extent, I did not acquire till after many experiments. At last, by preserving exactly the same posture after exhaustion of the lungs before the inspiration of the gas to be experimented upon, and during its compleat expiration, I found that I could always retain nearly the same quantity of gas in the bronchial vessels and fauces; the difference in the volume expired at different times, never amounting to a cubic inch and half.

By connecting the conducting pipe of the mercurial airholder, during the respiration of the gas, with a small trough of mercury by means of a curved tube, it became a perfect and excellent breathing machine. For by exerting a certain pressure on the airholding cylinder, it was easy to throw a quantity of gas after every inspiration or expiration, into tubes filled with mercury standing in the trough. In these tubes it could be accurately analised, and thus the changes taking place at different periods of the process ascertained.

Whenever I breathed pure nitrous oxide in the mercurial airholder, after a compleat voluntary exhaustion of my lungs, the pleasurable delirium was very rapidly produced, and being obliged to stoop on the cylinder, the determination of blood to my head from the increased arterial action in less than a minute became so great, as often to deprive me of voluntary power over the muscles of the mouth. Hence, I could never rely on the accuracy of any experiment, in which the gas had been respired for more than three quarters of a minute.

I was able to respire the gas with great accuracy for more than half a minute; it at first, rather increasing than diminishing the power of volition; but even in this short time, very strong sensations were always produced, with sense of fulness about the head, somewhat alarming; a feeling which hardly ever occurs to me when the gas is breathed in the natural posture.

In all the numerous experiments that I made on the respiration of nitrous oxide in this way, a very considerable diminution of gas always took place; and the diminution was generally apparently greater to the eye during the first four or five inspirations.

The residual gas of an experiment was always examined in the following manner. After being transferred through mercury into a graduated cylinder, a small quantity of concentrated solution of caustic potash was introduced to it, and suffered to remain in contact with it for some hours; the diminution was then noted, and the quantity of gas absorbed by the potash, judged to be carbonic acid. To the remainder, twice its bulk of pure water was admitted. After agitation and rest for four or five hours, the absorption by this was noticed, and the gas absorbed considered as nitrous oxide. The residual unabsorbable gas was mingled over water with twice its bulk of nitrous gas; and by this means, its composition, whether it consisted wholly of nitrogene, or of nitrogene mingled with small quantities of oxygene, ascertained.

From a number of experiments made at different times on the respiration of nitrous oxide, I select the following as the most accurate.

E. 1. At temperature 54°, I breathed 102 cubic inches of nitrous oxide, which contained near ¹/₅₀ common air, for about half a minute, seven inspirations and seven expirations being made. After every expiration, an evident diminution of gas was perceived; and when the last full expiration was made, it filled a space equal to 62 cubic inches.

These 62 cubic inches analised, were found to consist of

Carbonic acid 3,2

Nitrous oxide 29,0

Oxygene 4,1

Nitrogene 25,7

62,0

Hence, accounting for the two cubic inches of common air previously mingled with the nitrous oxide, 71 cubic inches had disappeared in this experiment.

In the last respirations, the quantity of gas was so much diminished, as to prevent the full expansion of the lungs; and hence the apparent diminution was very much less after the first four inspirations.

E. 2. At temperature 47°, I breathed 182 cubic inches of nitrous oxide, mingled with 2½ cubic inches of atmospheric air, which previously existed in the airholder, for near 40 seconds; having in this time made 8 respirations. The diminution after the first full inspiration, appeared to a by-stander nearly uniform. When the last compleat expiration was made, the gas filled a space equal to 128 cubic inches, the common temperature being restored. These 128 cubic inches analised, were found to consist of

Carbonic acid 5,25

Nitrous oxide 88,75

Oxygene 5,00

Nitrogene 29,00

Consequently, in this experiment, 93,25 cubic inches of nitrous oxide had disappeared.

In each of these experiments, the cylinder was covered with condensed watry vapor exactly in the same manner as if common air had been breathed in it. It ought to be observed that, E. 1. was made in the morning, four hours and half after a moderate breakfast; whereas, E. 2. was made but an hour and quarter after a plentiful dinner; at which near three fourths of a pint of table-beer had been drank.

From these experiments we learn, that nitrous oxide is rapidly absorbed by the venous blood, through the moist coats of the pulmonary veins. But as after a compleat voluntary exhaustion of the lungs, much residual air must remain in the bronchial vessels and fauces, as appears from their incapability of compleatly collapsing, it is evident that the gas expired after every inspiration of nitrous oxide mast be mingled with different quantities of the residual gas of the lungs;[192] whilst after a complete expiration, much of the unabsorbed nitrous oxide must remain as residual gas in the lungs. Now when a complete expiration is made after the breathing of atmospheric air, it is evident that the residual gas of the lungs consists of nitrogene,[193] mingled with small portions of oxygene and carbonic acid. And these are the only products found after the respiration of nitrous oxide.

To ascertain whether these products were partially produced, during the process of respiration, as I was inclined to believe from the experiments in the last section, or whether they were wholly the residual gases of the lungs, I found extremely difficult.

I at first thought of breathing nitrous oxide immediately after my lungs had been filled with oxygene; and to compare the products remaining after the full expiration, with those produced after a full expiration of pure oxygene; but on the supposition that oxygene and nitrous oxide, when applied together to the venous blood, must effect changes in it different from either of them separately, the idea was relinquished.

I attempted to inspire nitrous oxide, after having made two inspirations and a complete expiration of hydrogene; but in this experiment the effects of the hydrogene were so debilitating, and the consequent stimulation by the nitrous oxide so great, as to deprive me of sense. After the first three inspirations, I lost all power of standing, and fell on my back, carrying in my lips the mouth-piece separated from the cylinder, to the great alarm of Mr. Patrick Dwyer, who was noting the periods of inspiration.

Though experiments on successive inspirations of pure nitrous oxide might go far to determine whether or no any nitrogene, carbonic acid and oxygene were products of respiration, yet I distinctly saw that it was impossible in this way to ascertain their quantities, supposing them produced, unless I could first determine the capacity of my lungs; and the different proportions of the gases remaining in the bronchial vessels after a compleat expiration, when atmospheric air had been respired.

In some experiments (that I made on the respiration of hydrogene, with a view to determine whether carbonic acid was produced by the combination of carbon loosely combined in the venous blood, with the oxygene respired, or whether it was simply given out as excrementitious by this blood) I found, without however being able to solve the problem I had proposed to myself, that in the respiration of pure hydrogene, little or no alteration of volume took place; and that the residual gas was mingled with some nitrogene, and a little oxygene and carbonic acid.

From the comparison of these facts with those noticed in the last section and in R. III. Div. I. there was every reason to suppose that hydrogene was not absorbed or altered when respired: but only mingled with the residual gases of the lungs. Hence, by making a full expiration of atmospheric air, and afterwards taking six or seven respirations of hydrogene in the mercurial airholder, and then making a compleat expiration, I conjectured that the residual gas and the hydrogene would be so mingled, as that nearly the same proportions should remain in the bronchial vessels, as in the airholder. By ascertaining these proportions and calculating from them, I hoped to be able to ascertain with tolerable exactness, the capacity of my fauces and bronchia, as well as the composition of the gas remaining in them, after a complete expiration of common air.

IV. Respiration of Hydrogene.

The hydrogene that I employed, was procured from the decomposition of water by means of clean iron filings and diluted sulphuric and muriatic acids. It was breathed in the same manner as nitrous oxide, in the large mercurial airholder.

After a compleat voluntary exhaustion of my lungs in the usual posture, I found great difficulty in breathing hydrogene for so long as half a minute, so as to make a compleat expiration of it. It produced uneasy feelings in the chest, momentary loss of muscular power, and sometimes a transient giddiness.

In some of the experiments that I made; on account of the giddiness, the results were rendered inconclusive, by my removing my mouth from the mouth-piece after expiration, before the assistant could turn the stop-cock.

The purity of the hydrogene was ascertained immediately before the experiment by the test of nitrous gas, and by detonation with oxygene or atmospheric air; generally 12 measures of atmospheric air were fired with 4 of the hydrogene, and if the diminution was to ten or a little more, the gas was judged to be pure.

After the experiment, when the compleat expiration had been made and the common temperature restored; the volume of the gas was noticed, and then a small quantity of it thrown into the mercurial apparatus by means of the conducting tube, to be examined. The carbonic acid was separated by from it by means of solution of potash or strontian; the quantity of oxygene it contained, was ascertained by means of nitrous gas of known composition; the superabundant nitrous gas was absorbed by solution of muriate of iron; and the proportions of hydrogene and nitrogene in the remaining gas, discovered by inflammation with atmospheric air or oxygene in the detonating tube by the electric spark.

a. The two following experiments made upon quantities of hydrogene, equal to those of the nitrous oxide respired in the experiments in the last section, are given as the most accurate of five.

E. 1. I respired at 59° 102 cubic inches of hydrogene apparently pure, for rather less than half a minute, making in this time seven quick respirations.

After the complete expiration, when the common temperature was restored, the gas occupied a space equal to 103 cubic inches nearly. These analised were found to consist of

Carbonic acid 4,0

Oxygene 3,7

Nitrogene 17,3

Hydrogene 78,0

103,0

Now as in this experiment, the gas was increased in bulk only a cubic inch; supposing that after the compleat expiration the gas in the lungs, bronchia and fauces was of nearly similar composition with that in the airholder, and that no hydrogene had been absorbed by the blood, it would follow that 24 cubic inches of hydrogene remained in the internal organs of respiration, and consequently, by the rule of proportion, about 7,8 of the mixed residual gas of the common air. And then the whole quantity of residual gas of the lungs, supposing the temperature 59°, would have been 31,8 cubic inches; but as its temperature was nearly that of the internal parts of the body, 98°, it must have filled a greater space; calculating from the experiments of Guyton and Vernois,[194] about 37,5[195] cubic inches.

From the increase of volume, it would appear that a minute quantity of gas had been generated during the respiration, and this was, as we shall see hereafter, most probably carbonic acid.[196] Likewise there is reason to suppose, that a little of the residual oxygene must have been absorbed. Making allowances for those circumstances, it would follow, that the 37,5 cubic inches of gas remaining in my lungs, after a compleat expiration of atmospheric air at animal heat 98°, equal to 31,8 cubic inches at 59°, were composed of

Nitrogene 21,9

Carbonic acid 4,9

Oxygene 5,0

31,8

E. 2. I respired for near a half a minute in the mercurial airholder at 61°, 182 cubic inches of hydrogene; having made during this time, six long inspirations. After the last expiration, the gas filled a space nearly equal to 184 cubic inches, and analised, was found to consist of

Carbonic acid 4,8

Oxygene 4,6

Nitrogene 21,0

Hydrogene 153,6

184,0

Now in this experiment, reasoning in the same manner as before, 28,4 cubic inches of hydrogene must have remained in the lungs, and likewise 5,5 of the atmospheric residual gas. Consequently, the whole residual gas was nearly equal to 34 cubic inches at 61°, which at 98° would become about 40,4 cubic inches. And reasoning as before, it would appear from this experiment, that the quantity of gas remaining in my lungs after a compleat voluntary respiration, equalled at 98, about 40 cubic inches, and at 61°, 34 nearly: making the necessary corrections; that after common air had been breathed, these 34 cubic inches consisted of

Carbonic acid 4,1

Oxygene 5,5

Nitrogene 24,4

b. It would have been possible to prove the truth of the postulate on which the experiments were founded, by respiring common air or oxygene after the compleat expiration of the hydrogene, for the same time as the hydrogene was respired and in equal quantities.

For if portions of hydrogene were found in the airholder equal to those of the residual gases in the two experiments, it would prove that a uniform mixture of residual gas with the gas inspired, was produced by the respiration. That this mixture must have taken place, appeared, however, so evident from analogous facts, that I judged the experimental proof unnecessary.

Indeed, as most gases, though of different specific gravities, when brought in contact with each other, assume some sort of union, it is more than probable, that gas inspired into the lungs, from being placed in contact with the residual gas on such an extensive surface, must instantly mingle with it. Hence, possibly one deep inspiration and compleat expiration of the whole of a quantity of hydrogene, will be sufficient to determine the capacity of the lungs after compleat voluntary exhaustion, and the nature of the residual air.

That two inspirations are sufficient, appears probable from the following experiment.

E. 3. After a compleat voluntary expiration of common air, I made two deep inspirations of 141 cubic inches of hydrogene. After the compleat expiration, they filled a space equal to rather more than 142 cubic inches, and analised, were found to consist of

Carbonic acid 3,1

Oxygene 4,5

Nitrogene 18,8

Hydrogene 115,6

142,0

Now calculating on the exhausted capacity of my lungs from this experiment, supposing uniform mixture, they would contain after expiration of common air, about 30,7 cubic inches at 58°, equal to 36 at 98°, composed of about

Nitrogene 20,9

Oxygene 5,8

Carbonic acid 4,0

30,7

One should suppose a priori that in this experiment much less of the residual oxygene of the lungs must have been absorbed, than in Expts. 1 and 2; yet there is no very marked difference in the portions evolved. That a tolerably accurate mixture took place, appears from the quantity of nitrogene. The smaller quantity of carbonic acid is an evidence in favour of its evolution from the venous blood.

c. It is reasonable to suppose that the pressure upon the residual gas of the exhausted lungs, must be nearly equal to that of the atmosphere. But as aqueous vapour is perpetually given out by the exhalents, and perhaps evolved from the moist coats of the pulmonary vessels, it is likely that the residual gas is not only fully saturated with moisture at 98°, but likewise impregnated with uncombined vapor; and hence its volume enlarged beyond the increment of expansion of temperature.

Considering all these circumstances, and calculating from the mean of the three experiments on the composition of the residual gas, I concluded,

1st. That the exhausted capacity of my lungs was equal to about 41 cubic inches.

2dly. That the gas contained in my bronchial vessels and fauces, after a compleat expiration of atmospheric air, was equal to about 32 cubic inches, its temperature being reduced to 55°.

3dly. That these 32 cubic inches were composed of about

Nitrogene 23,0

Carbonic acid 4,1

Oxygene 4,9

d. In many experiments made in the mercurial airholder on the capacity of my lungs under different circumstances, I found that I threw out of my lungs by a full forced expiration at temperatures from 58° to 62°

cub. in. cub. in.

After a full voluntary inspiration, from 189 to 191

After a natural inspiration, from 78 to 79

After a natural expiration, from 67 to 68

So that making the corrections for temperature, it would appear, that my lungs in a state of voluntary inspiration, contained about 254 cubic inches; in a state of natural inspiration about 135; in a state of natural expiration, about 118; and in a state of forced expiration 41.[197]

As the exhausted capacity as well as impleted capacity of the internal organs of respiration must be different in different individuals, according as the forms and size of their thorax, fauces, and bronchia are different, it would be almost useless to endeavour to ascertain a standard capacity. It is however probable, that a ratio exists between the quantities of air inspired in the natural and forced inspiration, those expired in the natural and forced expiration, and the whole capacity of the lungs. If this ratio were ascertained, a single experiment on the natural inspiration and expiration of common air, would enable us to ascertain the quantity of residual gas in the lungs of any individual after a compleat forced expiration.[198]

V. Additional observations and experiments on the Respiration of Nitrous Oxide.

a. Having thus ascertained the capacity of my lungs, and the composition of the residual gas of expiration, I proceeded to reason concerning the experiments in section III, on the respiration of nitrous oxide.

In Exp. I. nearly 100 cubic inches of nitrous oxide, making the corrections on account of the common air, were respired for half a minute. In this time, they were reduced to 62 cubic inches, which consisted of 3,2 carbonic acid, 29 nitrous oxide, 4,1 oxygene, and 25,7 nitrogene.

But, as appears from the last section, there existed in the lungs before the inspiration of the nitrous oxide, about 32 cubic inches of gas, consisting of 23 nitrogene, 4,1 carbonic acid, and 4,9 oxygene, temperature being reduced to 59°. This gas must have been perfectly mingled with the nitrous oxide during the experiment; and consequently, the residual gas in the lungs after the experiment, was of the same composition as that in the airholder.

Supposing it as before, to be about 32 cubic inches: from the rule of proportion, they will be composed of

Nitrous oxide 14,7

Nitrogene 13,3

Carbonic acid 1,9

Oxygene 2,1

And the whole quantity of gas in the lungs and the airholder, supposing the temperature 59°, will equal 94 cubic inches, which are composed of

Nitrous oxide 43,7

Nitrogene 39,0

Carbonic acid 5,2

Oxygene 6,1

94

But before the experiment, the gas in the lungs and airholder equalled 134 cubic inches, and these, reckoning for the common air, were composed of

Nitrous oxide 100

Nitrogene, 24,3

Carbonic acid 4,1

Oxygene 5,6

Hence, it appears, that 56,3 cubic inches of nitrous oxide were absorbed in this experiment, and 13,7 of nitrogene produced, either by evolution from the blood, or decomposition of the nitrous oxide. The quantities of carbonic acid and oxygene approach so near to those existing after the respiration of hydrogene, that there is every reason to believe that no portion of them was produced in consequence of the absorption, or decomposition of the nitrous oxide.

b. In Exp. 2, calculating in the same manner, before the first inspiration, a quantity of gas equal to 216,5 cubic inches at 47°, existed in the lungs and airholder, and these 216,5 cubic inches were composed of

Nitrous oxide, 182,0

Nitrogene 24,9

Carbonic acid 4,1

Oxygene 5,5

216,5

After the compleat expiration, 160 cubic inches remained in the lungs and airholder, which was composed of

Nitrous oxide 110,6

Nitrogene 36,3

Carbonic acid 6,8

Oxygene 6,3

Hence, it appears, that 71,4 cubic inches of nitrous oxide were absorbed in this experiment, and about 12 of nitrogene produced. The quantity of carbonic acid and oxygene is rather greater than that which existed in the experiments on hydrogene.

c. From these estimations, I learned that a small quantity of nitrogene was produced during the absorption of nitrous oxide in respiration. It remained to determine, whether this nitrogene owed its production to evolution from the blood, or to the decomposition of a portion of the nitrous oxide.

Analogical evidences were not in favour of the hypothesis of decomposition. It was difficult to suppose that a body requiring the temperature of ignition for its decomposition by the most inflammable bodies, should be partially absorbed and partially decompounded at 98°, by a fluid apparently possessed of uniform attractions.

It was more easy to believe, that from the immense quantity of nitrogene taken into the blood in nitrous oxide; the system soon became overcharged with this principle, which not being wholly expended in new combinations during living action, was liberated in the aëriform state by the exhalents, or through the moist coats of the veins.

Now if the last rationale were true, it would follow, that the quantity of nitrogene produced in respiration, ought to be increased in proportion as a greater quantity of nitrous oxide entered into combination with the blood.

d. To ascertain whether this was the case, I made after full voluntary exhaustion of my lungs, one full voluntary inspiration and expiration of 108 cubic inches of nitrous oxide. After this, it filled a space nearly equal to 99 cubic inches. The quantities of carbonic acid and oxygene in these were not determined; but by the test of absorption by water, they appeared to contain only 18 nitrogene; which is very little more than should have been given from the residual gas of the lungs.

In a second experiment, I made two respirations of 108 cubic inches of nitrous oxide nearly pure. The diminution was to 95. On analysing these 95, I found to my great surprise, that they contained only 17 nitrogene. Hence, I could not but suspect some source of error in the process.

I now introduced into a strong new silk bag, the sides of which were in perfect contact, about 8 quarts of nitrous oxide. From the mode of introduction, this nitrous oxide must have been mingled with a little common air, not however sufficient to disturb the results.

I then adapted a cork cemented to a long curved tube to my right nostril; the tube was made to communicate with the water apparatus; and the left nostril being accurately closed, and the mouth-piece of the silk bag tightly adapted to the lips, I made a full expiration of the common air of my lungs, inspired nitrous oxide from the bag, and by carefully closing the mouth-piece with my tongue, expired it through the curved tube into the water apparatus. In this way, I made nine respirations of nitrous oxide. The expired gas of the first respiration was not preserved; but part of the gas of the second, third, fifth, seventh and ninth, were caught in seperate graduated cylinders. The second, analised by absorption, consisted of about 29 absorbable gas, which must have been chiefly nitrous oxide; and 17 unabsorbable gas, which must have been chiefly nitrogene; and the third of 22 absorbable gas, and 8 unabsorbable. The fifth was composed of 27 to 6; the seventh of 23 to 7, and the ninth of 26 to 11.

e. Though the results of these experiments were not so conclusive as could be wished; yet, comparing them with those of the experiments in section III. it seemed reasonable to conclude, that the production of nitrogene was increased, in proportion as the blood became more fully impregnated with nitrous oxide.

From this conclusion, compared with the phænomenon noticed in section 2, and in Div. I. section 4, I am induced to believe that the production of nitrogene during the respiration of nitrous oxide, is not owing to the decomposition of part of the nitrous oxide, in the aëriform state immediately by the attraction of the red particles of venous blood for its oxygene; but that it is rather owing to a new arrangement produced in the principles of the impregnated blood, during circulation; from which, becoming supersaturated with nitrogene, it gives it out through the moist coats of the vessels.

For if any portion of nitrous oxide were decomposed immediately by the red particles of the blood, one should conjecture, that the quantity of nitrogene produced, ought to be greater during the first inspirations, before these particles became fully combined with condensed oxygene. If on the contrary, the whole of the nitrogene and oxygene of the nitrous oxide were both combined with the blood, and carried through the pulmonary veins and left chamber of the heart to the arteries; then, supposing the oxygene chiefly expended in living action, whilst the nitrogene was only partially consumed in new combinations, it would follow, that the venous blood of animals made to breathe nitrous oxide, hyper-saturated with nitrogene, must be different from common venous blood; and this we have reason to believe from the phænomena in Div. I. section 4, is actually the case.

f. Besides the nitrogene generated during the respiration of nitrous oxide, we have noticed the evolution of other products, carbonic acid,[199] and water.

Now as nearly equal quantities of carbonic acid are produced, whether hydrogene or nitrous oxide is respired, provided the process is carried on for the same time; there is every reason to believe, as we have said before, that no part of the carbonic acid produced, is generated from the immediate decomposition of nitrous oxide by carbon existing in the blood.

Consequently, in these experiments, it must be either evolved from the venous blood; or formed, by the slow combination of the oxygene of the residual air of respiration with the charcoal of the blood.

But if it was produced by the decomposition of residual atmospheric air, it would follow, that its volume must be much less than that of the oxygene of the residual air, which had disappeared; for some of this oxygene must have been absorbed by the blood, and during the conversion of oxygene into carbonic acid by charcoal, a slight diminution of volume is produced.

In the experiments when nitrous oxide and hydrogene were respired for about half a minute, the medium quantity of carbonic acid produced, was 5,6 cubic inches nearly.

Now we will assume, that the quantity of carbonic acid produced, is in the ratio of the oxygene diminished; and there is every reason to believe, that in the expiration of atmospheric air, the expired air and the residual air are nearly of the same composition.

Hence, no more carbonic acid can remain in the lungs or be produced from the residual gas after the compleat expiration of common air, than that which can be generated from a volume of atmospheric air equal to the residual gas of the lungs.

The residual gas of the lungs, after compleat expiration, equals at 55°, 32 cubic inches, and 32 cubic inches of common air contain 8.6 cubic inches of oxygene.

But in the experiments on the respiration of hydrogene, not only 5.6 cubic inches of carbonic acid were produced, but more than 4 of residual oxygene remained unabsorbed.

Hence it appears impossible that all the carbonic acid evolved from the lungs during the respiration of nitrous oxide or hydrogene could have been produced by the combination of charcoal in the venous blood with residual atmospheric oxygene: there is consequently every reason to believe that it is wholly or partially liberated from the venous blood through the moist coats of the vessels.

g. The water carried out of the lungs in solution by the expired gas of nitrous oxide, could neither have been wholly or partially formed by the decomposition of nitrous oxide. The coats of the vessels in the lungs, and indeed in the whole internal surface of the body, are always covered with moisture, and the solution of part of this moisture by the inspired heated gas, and its deposition by the expired gas, are sufficient causes for the appearance of the phænomenon.

There are no reasons for supposing that any of the residual atmospheric oxygene is immediately combined with fixed or nascent hydrogene, or hydrocarbonate, in the venous blood at 98°, by slow combustion, and consequently none for supposing that water is immediately formed in respiration.

The evolution of water from the vessels in the lungs, is almost certain from numerous analogies.

h. As from the experiments in section II. it appeared that nitrous oxide was capable of being combined with oxygenated blood, and vice versa, blood impregnated with nitrous oxide capable of oxygenation; I was curious to ascertain what changes would be effected in nitrous oxide when it was respired, mingled with atmospheric air or oxygene. For this purpose, without making a very delicate experiment, I breathed in the large mercurial airholder about 112 cubic inches of nitrous oxide, mingled with 44 of common air, for near half a minute, in the usual mode. The gas, after expiration, filled a space nearly equal to 119. I did not exactly ascertain the composition of the residual gas; it supported flame rather better than common air, and after the nitrous oxide was absorbed, gave much less diminution with nitrous gas than atmospheric air.

i. I breathed a mixture of four quarts of nitrous oxide with three quarts of hydrogene, in a dry silk bag, for near a minute; an evident diminution was produced; but on account of the mode of experimenting it was impossible to determine the quantity of nitrous oxide absorbed, or the exact nature of the products. When a taper was introduced into a little of the residual gas, it inflamed with a very feeble explosion. Now a mixture of 4 parts nitrous oxide and 3 hydrogene, detonates when inflamed with very great violence.

k. Nitrous oxide can be respired without danger by the human animal for a much longer time than that required for the death of the smaller quadrupeds in it.

I have breathed it two or three times in a considerable state of purity, in a dry silk bag, for four minutes and quarter and four minutes and half: some diseased individuals have respired it for upwards of five minutes.

In the infancy of my experiments, from general appearances, I thought that the proportion of nitrous oxide absorbed in respiration was greater in the first inspirations than the last; but this I have since found to be a mistake. In the last respirations the apparent absorption is indeed less; but this is on account of the increased evolution of nitrogene from the blood. When nitrous oxide is respired for a long time, the last inspirations are always fuller and quicker than the first; but the consumption by the same individual is nearly in the ratio of the time of respiration. Three quarts, i. e. about 174 cubic inches, are consumed so as to be unfit for respiration, by an healthy individual with lungs of moderate capacity, in about a minute and quarter; six quarts, or 348 cubic inches, last generally for two minutes and half or two minutes and three quarters; eight quarts, or 464 cubic inches, for more than three minutes and half; and twelve, or 696 cubic inches, for nearly five.

The quantities of nitrous oxide absorbed by the same individual, will, as there is every reason to suppose, be different under different circumstances, and will probably be governed in some measure by the state of the health. It is reasonable to suppose, that the velocity of the circulation must have a considerable influence on the absorption of nitrous oxide; probably in proportion as it is greater a larger quantity of gas will be consumed in equal times.

I am inclined from two or three experiments, to believe that nitrous oxide is absorbed more rapidly after hearty meals or during stimulation from wine or spirits, than at other times. As its absorption appears to depend on a simple solution in the venous blood; probably diminution of temperature will increase its capability of being absorbed.

l. The quantities of nitrous oxide absorbed by different individuals, will probably be governed in some measure by the size of their lungs and the surface of the blood vessels, all other circumstances being the same.

From the observations that I have been able to make on the absorption of nitrous oxide, as compared with the capacity of the lungs, the range of the consumption of different individuals does not extend to more than a pint, or 30 cubic inches at the maximum dose.

We may therefore conclude, that the medium consumption of nitrous oxide by the respiration of different individuals, is not far from two cubic inches, or about a grain every second, or 120 cubic inches, or 60 grains every minute.

m. When nitrous oxide is breathed in tight silk bags, towards the end of the experiment as the internal surface becomes moist, as I have before mentioned, a certain quantity of common air penetrates through it and becomes mixed with the residual gas of the experiment; but this quantity is always too small to destroy any of the effects of the nitrous oxide. The residual gas of the common air, the nitrogene and carbonic acid produced in the process, and the residuum of the admitted atmospheric air, hardly ever amount after the experiment, to one half of the volume of the nitrous oxide absorbed. There is consequently, a perfect propriety in successively inspiring and expiring the whole of a given quantity of nitrous oxide, till it is nearly consumed. In the respiration of nitrous oxide as the gas is absorbed and not decomposed, little will be gained in effect, by perpetually inspiring and expiring new portions, whilst an immense quantity of gas will be idly wasted, and this circumstance, considering the expence of the substance, is of importance.

VI. On the respiration of Atmospheric Air.

Having thus ascertained the absorption of nitrous oxide in respiration, and the evolution of nitrogene and carbonic acid from the lungs during its absorption: considering atmospheric air as a compound in which principles identical with those in nitrous oxide existed, though in different quantities and looser combination, I was anxious to compare the changes effected in this gas by respiration, with those produced in nitrous oxide and oxygene; particularly as they are connected with the health and life of animals.

The ingenious experiments of Lavoisier and Goodwyn, prove the consumption of oxygene in respiration, and the production of carbonic acid. From many experiments on the respiration of common air, Dr. Priestly suspected that a certain portion of nitrogene, as well as oxygene, was absorbed by the venous blood.

b. In the following experiments on the respiration of atmospheric air in the mercurial airholder; the composition of the gas before inspiration and after expiration, was ascertained in the following manner.

Forty measures of it were agitated over mercury in solution of caustic potash, and suffered to remain in contact with it for two or three hours. The diminution was noted, and the gas absorbed judged to be carbonic acid. Twenty measures of the gas, freed from carbonic acid, were mingled with thirty of nitrous gas, in a tube of,5 inches diameter; they were not agitated,[200] but suffered to rest for an hour or an hour and half, when the volume occupied by them was noticed: and 50-m the volume occupied, divided by 3 considered as the oxygene x, and 20-x considered as the nitrogene.

c. To ascertain the changes effected in atmospheric air by single inspirations,

I made, after a compleat voluntary exhaustion of my lungs, at temperature 61°, one inspiration and expiration of 141 cubic inches of atmospheric air. After expiration, they filled a space equal to 139 cubic inches nearly. These 139 cubic inches analised were found to consist of

Nitrogene 101

Oxygene 32

Carbonic acid 6

The 141 cubic inches before inspiration, were composed of 103 nitrogene, 1 carbonic acid and 37 oxygene. The time taken to perform the inspiration and full expiration, was nearly a quarter of a minute.

I repeated this experiment seven or eight times, and the quantity of oxygene absorbed was generally from 5 to 6 cubic inches, the carbonic acid formed from 5 to 5,5, and the quantity of nitrogene apparently diminished by from 1 to 3 cubic inches.

E. 2. I made, after a voluntary expiration of common air, one inspiration and full expiration of 100 cubic inches of atmospheric air. It was diminished nearly to 98¾ or 99 cubic inches, and analised, was found to consist of

Nitrogene 71,7

Oxygene 22,5

Carbonic acid 4,5

This experiment I likewise repeated four or five times, with very little difference of result, and there always seemed to be a small diminution of nitrogene. I made no corrections on account of the residual air of the lungs in these processes, because there was every reason to suppose that it was always of similar composition.

c. Before I could ascertain whether similar changes were effected in atmospheric air, by natural inspirations as by forced ones, I was obliged to practise respiration in the mercurial airholder, by differing the conducting tube to communicate with the atmosphere till I had attained the power of breathing in it naturally, without labor or attention; I then found by a number of experiments, that I took into my lungs at every natural inspiration, about 13 cubic inches of air, and that I threw out of my lungs at every expiration,[201] rather less than this quantity; about 12¾ cubic inches.

The mean composition of the 13 cubic inches of air inspired, was

cub. in.

Nitrogene 9,5

Oxygene 3,4

Carbonic acid 0,1

That of the 12,7 of air expired

Nitrogene 9,3

Oxygene 2,2

Carbonic acid 1,2