Front matter (continued 4)

Quitting, therefore, all doubtful conjectures, I shall rest on facts and observations. I find, that the reproduction of beings is formed in many different manners; but, at the same time, I clearly perceive, that it is by the union of the organic particles sent back from every part of the individual, that the reproduction of vegetables and animals are effected. I am certain of the existence of these organic and active molecules in the seminal liquors of male and female animals and seed of vegetables; and cannot doubt but every species of reproduction is accomplished by the union of these organic molecules. Nor can I doubt, that in the generation of animals, and particularly in that of man, that the male and female particles mix in the formation of the fœtus, since we see infants which resemble both father and mother; and what confirms this conclusion is, that those parts, common to both sexes, mix promiscuously; whereas those never mix which represent the sexual parts. For we every day see children with eyes like the father, and the forehead and mouth like the mother; but we never find a like mixture of the sexual parts; it never happens that they have the testicles of the father, and the vagina of the mother, for even the fact of hermaphrodites is very doubtful.

In the parts of generation of the two sexes in the human species, there is so much resemblance, and so singular a conformity, that we might be inclined to think those which appear so different externally, are at bottom the same organs, only more or less developed; this was the opinion of the ancients, and M. Daubenton's ideas on this subject appear to me very ingenious.

The formation of the fœtus is, then, made by the union of the organic particles contained in the mixture of the seminal liquor of both sexes; this union produces the local establishment of the particles, which determines them to arrange themselves as they were in the individuals which furnished them; insomuch, that the molecules, which proceed from the head, cannot, by virtue of these laws, place themselves in the legs, or any other part of the fœtus. All these molecules must be in motion when they unite, and in a motion which must cause them to tend to a kind of centre, about which the union is made. This centre, or fixed point, which is necessary to the union of the molecules, and which, by its re-action and inertia, fixes the activity, and destroys the motion, is, probably, the first assemblage of the molecules which proceed from the sexual parts of the other individual; they must arrange under the form of an organized body which will not be another fœtus, for the reasons we have before given.[AC]

On the whole, I conceive there are organic particles of the sexual parts, which serve as a fixed point, or a centre of union, around which all the other parts that form the embryo collect. I speak of it only as probable; but as they are the only particles which differ, I have thought it more natural to imagine, that it is around these different particles the union is formed than those which are common to both sexes.

We have before observed, that those who have imagined the heart was the first formed, are deceived: those who say it is the blood, are no less so. All is formed at the same time. If we only consult observation, the chicken is seen in the egg before it has been sat upon; we perceive the spine of the back and the head, and, at the same time, the appendages which form the placenta. I have opened a great number of eggs, before and after incubation; and I am convinced, by my sight, that the chicken exists entirely in the middle of the cicatrice, the moment it comes from the body of the hen. The heat, communicated to it by incubation, only expands the parts by setting the liquors in motion; but it is not possible to determine which parts of the fœtus are fixed in the instant of formation.

I have always said, that the organic molecules were fixed, and that their uniting was caused only by their loss of motion. This appears to me certain: for, if we separately examine the seminal liquor of the male and female, we shall see an infinity of small bodies in great motion, but being mixed, their motion is instantly suspended, and heat is necessary to renew their activity; for the chicken which exists in the centre of the cicatrice is without any motion before incubation; and even twenty-four hours after, when it begins to become perceptible with a microscope, there is not the least appearance of motion then, nor even the day following. During the first day it is only a small white mucilaginous mass, which is of a consistence on the second, and insensibly increases, but whose motion is very slow, and does not at all resemble that of the organic particles which move rapidly in the seminal liquor. Besides, I have reason to say, that this motion of the organic molecules is absolutely destroyed; for if we keep an egg without exposing it to a degree of heat necessary to expand the chicken, the embryo, although formed entirely, will remain without any motion; and the organic molecules of which it is composed, will remain fixed without being able to give motion and life to the embryo which has been formed by their union. Thus, after the motion of the organic molecules has been destroyed, after the union of these molecules, necessary to form an animal body, there is still an external agent required to animate and give it life and motion; and this agent is heat, which, by rarefying the liquors, obliges them to circulate and put also every organ in action, which afterwards do no more than develope and grow, provided that this external heat continues to assist them in their functions.

Before the action of this external heat, not the least appearance of blood is to be seen; and it is not till twenty-four hours after, that I have perceived any change in the colour of the vessels. The blood first appears in the placenta, which communicates with the body of the chicken: but this blood seems to lose its colour as it approaches the body of the animal; for the chicken is entirely white, and we with difficulty discover in the first, second, and third days after incubation, a few small sanguinary points which are close to the body of the animal, but which seem not to make part of it, although it is these sanguinary points which afterwards form the heart. Thus, the formation of the blood is a change occasioned in the liquors by the motion heat communicates to them, and this blood is formed even out of the body of the animal, the whole substance of which is then only a kind of mucilage, or thick jelly.

The fœtus, as well as the placenta, derives the necessary nutriment for expansion, by a kind of absorption, and they assimilate the organic parts of the liquor in which they float: for the placenta cannot be said to nourish the animal, no more than the animal nourishes the placenta; since, if the one nourished the other, the first would soon appear to diminish, while the other increased, whereas both increase together, I have indeed observed in eggs, that the placenta at first increases much more in proportion than the fœtus, and therefore it may nourish the animal, or rather convey the nutriment to it, by intussusception.

What we have just said concerning the chicken, is easily applied to the human fœtus, which is formed by the union of the organic molecules of the two sexes. The membranes, and placenta, are formed from the superabundance of the particles which have entered into the composition of the embryo: which is then inclosed in a double membrane, where there is also a quantity of liquor, which is, perhaps, at first, but a portion of the semen of the father and the mother; and as the fœtus does not quit the matrix, it enjoys, from the instant even of its formation, an external heat necessary for its expansion; this heat communicates a motion to liquors, and sets the organs in play, and blood is formed in the placenta, and in the body of the embryo, by the motion occasioned by this heat. It may be even said, that the formation of the blood of the infant is as independent of the mother, as that which passes into the egg, is of the hen which hatches it, or of the oven which heats it.

It is certain, that the fœtus, placenta, and membranes, grow by intussusception: for, in the earliest days of conception, the pouch, which contains the whole product of generation, is not adherent to the matrix. De Graaf, in his experiments on doe rabbits, made these globules, wherein the whole business of generation lies, move about in the matrix. Thus, in the first stages, they increase and grow by drawing nutriment from the liquors which bathe the matrix, to which they are afterwards attached by a mucilage, in which small vessels are formed with time, as we shall hereafter explain.

But, not to quit the subject, let us return to the immediate formation of the fœtus, on which there are many remarks to be made, both as to its situation, and the different circumstances which may prevent or stop its formation.

In the human species, the seed of the male enters into the matrix, the cavity of which is considerable; and when it meets with a sufficient quantity of female semen, a mixture of the organic particles succeed, and the formation of the fœtus ensues: the whole, perhaps, is done instantaneously, especially if the liquors are both in an active and flourishing state. The place where the fœtus is formed, is the cavity of the matrix, because the seed of the male can enter there more easily than into the trunks; and as this viscera has but one small orifice, which is always shut, excepting when the ardour of love causes it to open, the materials of generation remain there with safety, and scarcely ever reissue but by rare and unfrequent circumstances: but as the liquor of the male sprinkles the vagina, before it penetrates the matrix, by the activity of the organic molecules which compose it, it may go farther into the trunks, and, perhaps, into the ovarium. As the liquor of the female has already its perfection in the glandular bodies of the testicles, from which it flows and moistens the trunks and other parts before it descends into the matrix, and as it may issue out of the vacuities left around the neck of the matrix, it is not impossible, that the mixture of the two liquors may be made in all these different places. It is, therefore, probable that fœtuses are often formed in the vagina, but which fall out as soon as they are formed, because there is nothing to retain them. It may also sometimes happen, that fœtuses are formed in the trunks; but this case is very rare, and cannot happen but when the seminal liquor of the male enters the matrix in great plenty.

The collection of anatomical observations makes mention of fœtuses not only being found in the trunks, but also in the testicles. In the History of the Old Academy of Sciences, (vol. II. page 91.) we meet with an observation on this subject. M. Theroude, a surgeon at Paris, shewed the academy an unformed mass, which he found in the right testicle of a girl of eighteen years of age. In it were two open slits, furnished with hair like two eye-lids, above which was a kind of forehead, with a black line instead of eyebrows; immediately over that were many hairs matted together in two separate lines, one of which was seven, and the other three inches long; under the great angle of the eye, two of the grinding teeth appeared to shoot, hard, thick, and white; they had their prongs, and a third tooth thicker than the rest above them. There appeared likewise other teeth at different distances from each other: two between these, of the canine nature, issued from an opening where the ear is placed. In the same volume, page 144, it is related, that M. Mery found, in the testicle of a woman who had conceived, a bone of the upper jaw, with many teeth therein, so perfect that some appeared to be of more than ten years growth. We find, in the Journal de Medicine, for January 1683, published by the Abbé de la Roque, the history of a lady who died with the ninth child, which was formed in or near one of the testicles, which is not very clearly explained. The fœtus was about an inch in size, completely formed, and the sex easily to be distinguished. We also find, in the Philosophical Transactions, some observations on the testicles of women, wherein teeth, hair, and bones, have been found. If all these circumstances are true, we must suppose, that the seminal liquor of the male sometimes ascends, although very seldom, to the testicles of the female. Yet, notwithstanding all this, I have some difficulty to believe it; first, because the circumstances, which appear to prove it, are extremely rare: secondly, because a perfect fœtus has never been seen in the testicles but by M. Littre, who seems to relate it in a very suspicious manner: thirdly, because it is not impossible, that the seminal liquor of the female alone may produce organized masses, as moles, hair, bones, flesh, and, in short, because if we give credit to anatomists, fœtuses may be formed in the testicles of men, as well as in those of women: for we find, in the History of the Royal Academy, vol. II. p. 298, an observation of a surgeon, who says, he discovered in the scrotum of a man, the figure of a child inclosed in his membranes: and that the head, feet, eyes, bones, and cartilages, were distinguishable. If all these observations were equally true, we must necessarily adopt one of these two hypotheses, either that the seminal liquor, of each sex, cannot produce any thing without being mixed with that of the other sex, or that either of them can produce irregular masses of itself. By keeping to the first, we should be obliged to admit, to explain in all the circumstances we have related, that the liquor of the male sometimes ascends to the testicle, and, by mixing with the seminal liquor of the female, forms organized bodies; and so may also the female fluid, by being plentiful in the vagina, penetrate, during the time of copulation, into the scrotum of the male, nearly as the venereal virus often reaches that part; and that in this case, an organized body may be found in the scrotum, by the mixture of the male and female fluids; or, if we admit the other hypothesis, which appears to be the most probable, and suppose, that the seminal liquor of each individual may produce organized masses, then we may be able to say, that all these bony, fleshy, and hairy productions, sometimes found in the testicles of females, and in the scrotum of males, may derive their origin from the liquor of the individual in which they are found. But enough of observations upon facts, which appear to be as uncertain as inexplicable, for I am much inclined to believe, that, in certain circumstances, the seminal liquor of each individual may produce something alone and of itself, and that young girls might form moles without any communication with the male, as hens form eggs without having received the cock. I might support this opinion with observations which appear to me as credible as those I have quoted. M. de la Saone, physician and anatomist of the Academy of Sciences, published a memoir on this subject, in which he asserts, that religious nuns, though strictly cloistered, had formed moles. Why should that be impossible, since hens form eggs without communication with the cock? and in the cicatrice of these eggs we perceive a mole, with appendages, instead of a chicken? The analogy appears to me to have sufficient power for us, at least to doubt, or suspend our determination. Be this as it will, it is certain that the mixture of the two liquors are required to form a fœtus , and that this mixture cannot come to any effect but when it is in the matrix, where the anatomists have sometimes found fœtuses; and it is natural to imagine, that those which have been found out of the matrix, and in the cavity of the abdomen, have escaped by the extremity of the trunks, or by some accidental opening, and that they never fall from the testicles into the abdomen, because it is almost an impossibility that the seminal liquor of the male can ascend so high. Leeuwenhoek has computed the motion of these pretended spermatic animals to be four or five inches in forty minutes, which would be more than sufficient for the animalcules to traverse from the vagina into the matrix, from the matrix into the trunks, and from the trunks into the testicles, in an hour or two, provided all the liquor had that motion. But how is this to be conceived, that the organic molecules, whose motion ceases as soon as the liquid fails, can arrive as far as the testicles, unless brought there by the liquor in which they swim? This progressive motion cannot be given by the organic molecules to the liquor which it contains, therefore, whatever activity these molecules may be supposed to have, we cannot see how they can arrive at the testicles, and form a fœtus there, unless the liquor itself was pumped up and attracted thither, a supposition not only gratuitous but even against all human probability.

The doubts which this supposition gives rise to, confirm the opinion that the male fluid penetrates the matrix, and enters therein by the orifice, or across the membraneous coat of the viscera. The female fluid may also enter into the matrix, either by the opening at the upper extremity of the trunks, or across the skin even of the trunks and matrix. M. de Weirbrech, an able anatomist of Petersburg, confirms this opinion:——"Res omni attentione dignissima (says he) oblata mihi est in utero feminæ alicujus a me dissectæ; erat uterus ea magnitudine qua esse solet in virginibus, tubæque ambæ apertæ quidem ad ingressum uteri, ita ut ex hoc in illas cum specillo facile possem transire ac flatum injicere, sed in turbarum extremo nulla dabatur apertura, nullus aditus; fimbriarum enim ne vestigium quidem aderat, sed loco illarum bulbus aliquis pyriformis materia subalbida fluida turgens, in cujus medio fibra plana nervea, cicatriculæ æmula, apparebat, quæ sub ligamentuli specie usque ad ovarii involucra protendebatur.

"Dices, eadem a Regnero de Graaf jam olim notata. Equidem non negaverim illustrem hunc prosectorem in libro suo de organis mulieribus non modo similem tubam delineasse, Tabula XIX, fig. 3, sed & monuisse, 'tubas quamvis secundum ordinariam naturæ dispositionem in extremitate sua notabilem semper coarctationem habeant, præter naturam tamen aliquando claudi;' verum enimvero cum non meminerit auctor an id in utraque tuba ita deprehenderit; an in virgine; an status iste præternaturalis sterilitatem inducat: an vero conceptio nihilominus fieri possit; an a principio vitæ talis structura suam originem ducat; sive an tractu tempora ita degenerare tubæ possint; facile perspicimus multa nobis relicta esse problemata quæ, utcumque soluta, multum negotii facessant in exemplo nostro. Erat enim hæc femina maritata, viginti quatuor annos nata, quæ filium pepererat quem vidi ipse, octo jam annos natum. Dic igitur tubas ab incunabulis clausas sterilitatem inducere: quare hæc nostra femina peperit? Dic concepisse tubis clausis; quomodo ovulum ingredi tubam potuit? Dic coaluisse tubas post partum: quomodo id nosti? Quomodo adeo evanescere in utroque latere fimbriæ possunt, tanquam nunquam adfuissent? Si quidem ex ovario ad tubas alia daretur via, præter illarum orificium, unico gressu omnes superarentur difficultates; sed fictiones intellectum quidem adjuvant, rei veritatem non demonstrant; præstat igitur ignorationem fateri, quam speculationibus indulgere[AD]." The difficulties which occurred to this able author are insurmountable in the egg system, but which disappear in our explanation. This observation seems only to prove what we have observed, that the seminal liquor of both male and female may penetrate the coat of the matrix, and enter across the pores of the membranes; to be assured of it, it is only necessary to pay attention to the alteration that the seminal liquor of the male causes to the viscera, and to the kind of vegetation or expansion that it causes there. Besides, the liquor which issues by the vacuities of De Graaf, being of the same nature as the liquor of the glandular bodies, it is very evident that this liquor comes from the testicles, and yet there is no vessel through which it can pass; consequently we must conclude, that it penetrates the spongy coat of all these parts, and that it not only enters the matrix, but even can issue out when these parts are in irritation.

But even should we refuse this idea of penetration, we cannot deny that the liquor of the female, which flows from the glandular bodies of the testicles, may enter by the opening at the extremity of the trunk, as that of the male does by the orifice of the viscera; and that consequently these two liquors may mix of themselves in this cavity, and form there the fœtus in the manner we have explained.

CHAPTER XI.

OF THE EXPANSION, GROWTH, AND DELIVERY OF THE FŒTUS, &C.

In the expansion of the fœtus, two different degrees of growth make different kinds of expansion. The first, which succeeds immediately after the formation of the fœtus, is not proportionable in all the parts of which it is composed. The more distant it is from the formation, the more in proportion are its parts, and it is only after it has quitted the womb of its mother that the growth of the parts is made in nearly an equal manner. It must not be imagined that the figure of the fœtus, at the moment of formation, is absolutely like that of an adult. It is certain that the embryo contains every part which, must compose a man, but they differ in their successive expansion.

In an organized body, as that of an animal, we may suppose some parts are more essential than others, and though some may be useless or superfluous, there are some on which the rest seem to depend for their expansion and disposition. We must consider some as fundamental parts, without which the animal cannot exist, and which are more accessory and external, and appear to derive their origin from the first, and which seem to be formed as much for the ornament, symmetry, and external perfection of the animal, as for the necessity of its existence, and the exercise of the essential functions of life. These two kinds of different parts expand successively, and are almost equally apparent when the fœtus quits the womb; but there are others which Nature seems to keep in reserve, as the teeth, which do not appear for some time, and also the glandular bodies in the testicles of females, the beards of males, &c. which do not shew themselves till the age of puberty.

In order to discover the fundamental and essential parts of an animal body, we must pay attention to the number, situation, and nature of the whole; those which are simple, those whose position is invariable, and those without which the animal cannot exist, will be the essential parts; those, on the contrary, which are double, or in a greater number, those whose size and position vary, and those which may be retrenched from the animal without destroying or even doing it an injury, may be looked upon as less necessary, and more accessory, to the animal machine. Aristotle has said that the only parts essential to animals were those with which they take their nutriment, and throw out the superfluous parts of it from the body. From the mouth to the arms are simple parts, which no other can supply. The head and spine of the back are also simple parts, whose position is invariable. The spine of the back serves for a foundation to the fabric of the body; and it is from the marrow which it contains that the motion and action of most of the members and organs proceed; it is also this part which appears one of the first in the embryo. Now these simple parts which appear the first are all essential to the existence and form of the animal. There are many more double than simple parts in the body of an animal, and seem to be produced on each side of the simple parts by a kind of vegetation; for these double parts are similar in form, and different in position. The left hand exactly resembles the right, because it is composed of the same number of parts; nevertheless, if it was placed in the situation of the right, we could not make use of it for the same purposes, and should have reason to regard it as a very different member. It is the same with respect to the other double parts; they are similar as to form, and different as to the position which is connected to the body of the animal; and by supposing a line to divide the body into two equal parts, the position of all the similar parts would refer to this line as a centre.

The spinal marrow, and the vertebræ which contains it, appear to be the real axis, to which we must refer all the double parts of the animal, for they seem to derive their origin, and to be only symmetrical branches issuing from this trunk or common base, for we see the ribs shoot out on each side of the vertebræ in the young chicken as the young branches shoot out from the principal branch of a tree. In all embryos the middle of the head and vertebræ appear to be the first formed; afterwards we see on the two sides of a vesicle which forms the middle of the head two other vesicles which appear to proceed from the first. These two vesicles contain the eyes and the other double parts of the head; so likewise we perceive little tubercles shoot out in equal numbers from each side of the vertebræ, which extend by degrees and form the ribs, and other double parts of the trunk. On the side of this trunk already formed, as the conclusion, the legs and arms appear. This first expansion is very different from that which is made afterwards; it is the production of parts which appear for the first time; that which succeeds is only a growth of all the parts already created.

This symmetrical order of all the double parts found in every animal, the regularity of their position, the equality of their extension and growth, and the perfect resemblance between them, seem to indicate that they derive their origin from the simple parts; that there must reside in these simple parts a power which acts equally on each side, or, which answers the same meaning, they are the fixed points against which the power that produces the expansion of the double parts is exercised. That the power which acts on the right is equalled by that of the left side, and consequently they are counterbalanced by this re-action.

From hence we may infer, that if there is any defect or excess in the matter which is to serve for the formation of the double parts, as the powers which impel them on each side are equal, the defect or excess must be formed the same both on the right and left; for example, if, from a defect of matter, a man has but two fingers instead of five on the right hand, he will have but two on the left hand; or if, by an excess of matter, he has six fingers on one hand, he will have six on the other; or if the matter be vitiated, and causes an alteration in the right part, it will be the same on the left. This fact is very often seen. Most monsters are made with symmetry; the disarrangement of the parts of monsters appears to be made with order: Nature, therefore, even in her errors, mistakes as little as possible.

This harmony of position in the double parts of animals is found also in vegetables; branches shoot out from buds on every side; the veins in the leaves are equally disposed as to the principal vein; and although symmetrical order appears to be less exact in vegetables than in animals, it is only because it is more varied, and its limits are more extended, and less precise; but we may nevertheless easily discover this order, and distinguish the simple and essential parts from those which are double, and the latter we must regard as having taken their origin from the former. We shall more fully discuss this point, as far as relates to vegetables, when we come to treat of them.

It is not possible to determine under What form the double parts exist before expansion, nor in what manner they are folded, nor what figure results from their position by connection with the simple parts. The body of the animal, in the instant of formation, certainly contains every part which is to compose it; but the relative position of these parts must be very different then from what it becomes afterwards. It is the same with vegetables, for if we observe the expansion of a young leaf, we shall perceive that it is folded on both sides the principal vein, and that its figure does not resemble at that time what it afterwards assumes.

When we amuse ourselves by folding paper to form crowns, boats, &c. the different folds of the paper seem to have no resemblance to the form which must result by the unfolding; we only see that these folds are always made in an uniform order, and exactly the same on one side as that we have made on t he other; but it would be a problem beyond known geometry, to determine the figures which may result from all the unfoldings of a certain given number of folds. All what immediately relates to the position, is beyond our mathematical sciences. This art, which Leibnitz calls Analysis Situs, is not yet found out; though the art, which would shew us the connections that result from the position of things, would perhaps be more useful than that which has only bulk for its object, for we have often more need to know the form than the matter.

In the unfolding of Nature's productions, not only the folded parts take new positions, but they acquire, at the same time, extent and solidity. Since we cannot therefore determine the result of the simple unfolding of a folded form, in which, as in a piece of folded paper, there is but one change of position between the parts, without any augmentation or diminution of the bulk or mass of the matter, how is it possible for us to judge of the complex unfolding of the body of an animal, in which not only the relative position of the parts, but also their mass of matter, undergoes considerable changes? We cannot, therefore, reason upon this subject, but by drawing some inductions from the examination of the things at the different periods of their unfolding, and by assisting ourselves with the observations that we have had the opportunity to make.

It is true we see the chick in the egg before incubation; it floats in a transparent liquor, contained in a small purse, formed by a very fine membrane in the centre of the cicatrice; but this chick is then only a particle of inanimate matter, in which we cannot discern any organization, nor any determined figure. We judge by the external form that one of the extremities is the head, and the rest to be the spine of the back. It appears that this is the first product of fecundation resulting from the mixture of the seed of the male and female; nevertheless, before asserting this as a fact, there are many things should be considered. When the hen has cohabited with the cock for a few days, and afterwards separated from him, the eggs she produces for a month after separation are as fertile as those she produced during the time of cohabitation with the male, and unfold at the same time; they only require twenty-one days sitting, and the embryo of the one will be as forward and as completely formed as that of the other. From hence we might think, that this form, under which the chick at first appears to us in the egg, does not immediately proceed from a mixture of the two liquors, but that it existed in other forms during the time the egg remained in the body of the mother; for the embryo in the form we see it before incubation, requires only heat to unfold and bring it forth. Now, if it had this form twenty days, or a month before, when the egg was first fecundated, why was it not hatched by the internal heat of the hen? and why is not the chicken perfectly formed in those eggs which are fecundated twenty-one days before the hen lays them?

This difficulty is not so great as it appears; for we must conceive, that in the time of the cock's cohabitation with the hen, each egg receives in its cicatrice, wherein the female liquor is contained, a small portion of the semen of the male. The egg attached to the ovary is in oviparous females, what the glandular substance is in the testicles of viviparous females. The cicatrice of the egg corresponds with the glandular bodies in which the seminal liquor of the female resides; that of the male penetrates and mixes there with it; from this mixture, the formation of the embryo instantly results. The first egg which the hen lays after coition is fecundated, and capable of producing a chicken; those which she lays afterwards were fecundated at the same instant; but as there is still wanting essential parts to this egg, the production of which is independent of the seed of the male, as the white, membranes, and shell, the young embryo contained in the cicatrice cannot unfold in this imperfect egg, although assisted by the internal heat of the mother. It remains, therefore, in the cicatrice in the state in which it was formed, until the egg has acquired all the parts necessary to the growth and nourishment of the chicken: and it is not till the egg has attained its perfection that the embryo begins to unfold: this unfolding is performed by the external heat of incubation; but it is certain, if the egg could be confined within the body of the hen for 21 days after it was completely formed, the chicken would be produced, unless the internal heat of the hen should prove too powerful, for the degrees of heat necessary to hatch chickens are not very extended, and the least defect or excess is equally prejudicial to their unfolding. The last eggs the hen lays, containing the same as the first, proves nothing more than that the egg must acquire entire perfection before the embryo can unfold itself; and for want of the heat necessary to this unfolding, eggs may be kept a considerable time before incubation, without preventing the produce of the chickens they contain.

It appears, therefore, that the state of the embryo, when the egg is laid by the hen, is the first state which succeeds fecundation; that the form under which we see it is the first form resulting from the intimate mixture, and form the penetration of the two seminal liquors; and consequently by following, as Malpighius has done, this unfolding from hour to hour, we discover all that is possible to be known, unless we could see the two liquors mix before our eyes, and how the first arrangement of the particles are made, which produces the first form of the embryo.

If we reflect on this fecundation (which is made at the same time) of these eggs, which are laid successively, and along time after each other, we shall find new arguments against the existence of eggs in viviparous animals; for if the females of viviparous animals, or if women contained eggs, like hens, why are there not many fecund at the same time? why are not some of them produced in nine months, and others at distant periods? and when women have two or three children, why do they all come into the world at one time? If these fœtuses were produced by the means of eggs, would not they come successively, according as the eggs come to perfection, after the time of impregnation? And would not super-fœtation be as frequent as they now are scarce, or as natural as they appear to be accidental?

We cannot follow the unfolding of the fœtus in the matrix as we pursue that of the chick in the egg; the opportunities of observing it are few, and we can only know what anatomists, surgeons, and midwives have written thereon. It is by collecting all their particular observations, and by comparing their remarks and their descriptions, that we have made the following abridged history of the human fœtus.

There is a great appearance that, immediately after the mixture of the two seminal liquors, the whole materials of generation exist in the matrix under the form of a globe; since we know, by anatomists, that three or four days after conception there is a small oval ball in the matrix, this ball is formed by an extremely fine membrane, which incloses a limpid liquor like the white of an egg. We can then perceive some small united fibres in this liquor, which are the first outlines of the fœtus. A net-work of fine fibres collects on the surface of the ball, which extends from one of the extremities to the middle. These are the first vestiges of the placenta.

Seven days after conception we may distinguish, by the naked eye, the first lineaments of the fœtus, as yet unformed; being only a mass of transparent jelly, which has acquired some small degree of solidity; the head and trunk are easily discernible, because this mass is of an oblong form, and the trunk is more delicate and somewhat longer. Some small fibres, in form of a plume of feathers, spring from the body of the fœtus, and which turn towards the membrane in which it is included; these fibres are to form the umbilical cord.

Fifteen days after conception, the head, and the most apparent features of the face, are distinguishable; the nose resembles a small prominent and perpendicular thread affixed to a line, which indicates the division of the lips. Two small black points are in the places of the eyes, and two little holes in those of the ears; the body of the fœtus has also received some growth. On each side of the upper and inferior parts of the trunk, little protuberances appear, which are the first outlines of the arms and legs.

Eight days after, that is in three weeks, the body of the fœtus has only increased about a line; but the arms and legs, the hands and feet, are apparent; the growth of the arms is more quick than that of the legs, and the fingers separate sooner than the toes. At this time internal organization begins to be discernible; the bones appear like small threads as fine as hairs; the ribs are disposed regularly from the two sides of the back bone; and as well as the arms, legs, fingers, and toes, are represented by very small threads.

At a month the fœtus is more than an inch long; it naturally takes a curved posture, in the middle of the liquor which surrounds it, and the membranes which contain the whole are increased in extent and thickness; the mass is oval, and it is then about an inch and an half in its greatest, and an inch and a quarter the smallest diameter. The human figure is no longer equivocal, every part of the face is already discernible; the body is fashioned, the thighs and belly are seen, the limbs formed, the toes and fingers divided, the skin thin and transparent, the viscera marked by fibres, the vessels as fine as threads, and the membranes extremely delicate, the bones are as yet soft, and have only taken solidity in some few parts; the vessels which compose the umbilical cord, are as yet in a straight line by the side of each other; now the placenta only occupies a third of the whole mass; whereas in the beginning it occupied the half. It appears, therefore, that its growth, in superficial extent, has not been so great as that of the fœtus, and the rest of the mass; but it has increased much more in solidity; its thickness has become greater in proportion than the membranes of the fœtus, both of which are now easily distinguished.

According to Hippocrates, the male fœtus is developed sooner than the female. He says all parts of the body in the first are apparent in thirty, whereas the latter are not so till the expiration of forty-two days.

In six weeks the fœtus is nearly two inches long; the human figure begins to be more perfect; the head is only larger in proportion than the other parts of the body; the motion of the heart is perceived about this time. It has been seen to beat in a fœtus of sixty days, a long while after it had been taken out of the womb of its mother.

In two months the fœtus is more than two inches long; the ossification is discernible as far as the middle of the arm, thigh, and leg, and in the point of the lower jaw, which is then very forward before the upper. These, however, are only ossified points; but by the effect of a more ready expansion, the clavicles are wholly ossified. The umbilical cord is formed, and the vessels which compose it, begin to twist nearly like threads which compose a rope: but this cord is still very short in comparison of what it becomes hereafter.

In three months the fœtus is nearly three inches long, and weighs about three ounces. Hippocrates says, that it is at this time the motion of the male fœtus begins to be felt by its mother; but that those of the female are not felt till after the fourth; there are women who affirm they have felt the motions of the child at the beginning of the second month. It is very difficult to be certain on this subject, the sensations excited by the first motions of the fœtus depending, perhaps more on the sensibility of the mother than the strength of the child.

Four months after conception the length of the fœtus is six or seven inches; every part of its body is so greatly augmented as to be perfectly distinguished from each other; even the nails appear on the fingers and toes. The testicles of the males are shut up in the belly above the kidneys; the stomach is filled with somewhat of a thick humour, like that which incloses the amnios. We find a milky fluid in the little vessels, and in the large ones a black liquid matter. There is a little bile in the gall, and some urine in the bladder. As the fœtus floats freely in the liquid which surrounds it, there is always a space between the body and membranes in which it is contained. These coverings grow at first more than the fœtus; but after a certain time it is quite the contrary. Before the end of the third month the head is bent forward, the chin rests on the breast, the knees are lifted up, the legs bent backwards upon the thighs (sometimes the knees are so high as almost to touch the jaws), the arms are generally folded across the breast, and one of the hands, and often both touch the face. The fœtus afterwards takes different situations, as it acquires strength. Experienced midwives have pretended to be certain that it changes much oftener than is commonly thought, and which they prove by several observations; first, the umbilical cord is often found twisted round the body and limbs of the child, in a manner which necessarily supposes, that the fœtus has moved in many directions, and taken different positions; secondly, a mother feels the motions of the fœtus sometimes on one side of the womb and sometimes on another; and it often strikes against many different places, which must be occasioned by different positions, and supposes that it takes different situations; thirdly, as it floats in a liquid which surrounds it on all sides, it can very easily turn and extend itself by its own strength; and it must also take different situations according to the various attitudes of the mother; for example, when she lies down, the fœtus must be in another situation to what it was when she stood upright.

Most anatomists have said, that the fœtus is constrained to bend its body, because it is too confined in its covering; but this opinion does not appear well founded, for in the first five or six months there is more space than is required for the fœtus to extend, and yet during that time it is bent and folded. We also see the chicken is in a curved posture in the liquor of the amnios, although this membrane and its liquor are sufficient to contain a body five or six times as large as the fœtus. Thus we may conclude that this curved form of the fœtus is natural, and not the effect of force. I am somewhat of Harvey's opinion, who says, it takes this attitude because it is the most favourable to rest and sleep; and as the fœtus sleeps almost continually, it naturally takes the most advantageous situation. "Certe (says this famous anatomist) animalia omnia, dum quiescunt & dormiunt, membra sua ut plurimum adducunt & complicant, figuramque ovalem ac conglobatam quærunt: ita pariter embryones qui ætatem suam maxime somno transigunt, membra sua positione ea qua plasmantur (tanquam naturalissima ac maxime indolenti quietique aptissima) componunt[AE]."

The matrix, as we have already said, takes a very ready growth after conception, and it continues also to increase in proportion with the fœtus; but the fœtus at length outgrows the matrix, and then, especially when it approaches maturity, it may be too much confined, and agitate the matrix by reiterated motions and violent efforts. The mother sensibly feels the impression of these painful sensations, and which are called periodic pains after the labour commences. The more power the fœtus exerts to dilate the matrix the greater it finds the resistance, from the natural compression of the parts. From thence all the effect falls on the orifice, which has been increasing by degrees during the latter months of pregnancy. The head of the fœtus, forcibly inclining against the sides of the orifice, dilates it, by a continual pressure, till the moment of delivery, when it opens sufficiently for the child to escape from the womb.

What makes it probable that the labour-pains proceed only from the dilatation of the orifice of the matrix is, that this dilatation is the only means to discover whether the pains felt are in fact the pains of labour, for women often feel very sensible pains, which are not those that immediately precede delivery. To distinguish the false from true pains, it has been recommended for the midwife to touch the orifice of the matrix, as if the pains be true the dilatation will always increase, and if they are false pains, that is to say, pains which proceed from some other cause than that of the approaching delivery, the orifice will contract rather than dilate, or at least will not continue to dilate. From hence we have sufficient foundation to imagine, that these pains proceed from a forced dilatation of the orifice. The only thing which embarrasses on this occasion is that alternative of rest and sufferings the mother endures. This circumstance of the effect does not perfectly agree with the cause which we have just indicated; for the dilatation of an orifice, which is made by degrees, should produce a constant and continued pain, without any intervals of ease. But possibly the whole may be attributed to the separation of the placenta, which we know is fastened to the matrix by a number of papillæ, which penetrate into the vacuities or cavities of this viscera; therefore may it not be supposed that they do not separate from their cavities all at the same time; that each separation causes those acute pains, and the intervals between are those of ease and rest? The effect in this case perfectly answers the cause, and we can support this conjecture by another observation.—Immediately before delivery there issues a whitish and viscous liquor, like that which flows from the nipples of the placenta when drawn out of their places, which makes it probable that this liquor, which then issues from the matrix, is produced by the separation of some of the papillæ of the placenta.

It often happens that the fœtus quits the matrix without bursting the membranes, and consequently without the contained liquor flowing out. This kind of delivery appears to be most natural, and resembles that of most animals; nevertheless, the human fœtus commonly pierces its membranes by the resistance it meets with at the orifice of the matrix. It also sometimes brings away part of the amnios, and even the chorion, upon its head like a cap. When these membranes are pierced or torn, the liquors, called the waters, which they contain flow out, and the sides of the orifice of the matrix, and the vagina, being thus moistened, give way more easily to the passage of the child. After the flowing of this liquor there remains sufficient room in the matrix for the midwife to return the child, if the position is unfavourable. When the fœtus is come out the delivery is not entirely completed, the placenta and membranes remain in the matrix, and the new-born infant adheres to them by the umbilical cord; the hand of the midwife, or the weight of the body of the infant alone, draws them out by means of this cord. Those organs which were necessary to the life of the fœtus become useless, and even noxious to the new-born infant. They are instantly separated from the body of the child, by tying the umbilical cord about an inch distance from the navel, and by cutting it about an inch from the ligature. The remainder of this cord dries away, and separates of itself from the navel, about the sixth or seventh day.

On examining the fœtus previous to its birth we may form some idea of its natural functions. It has organs, which are necessary to it while in the womb of its mother, but which become useless. For the better understanding the mechanism of these functions, we must explain a little more particularly the nature of those necessary parts, the umbilical cord, the membranes, the liquor which they contain and the placenta. The umbilical cord, which is attached to the body of the fœtus at the navel, is composed of two arteries and one vein; these prolong the circulation of the blood, but the vein is larger than the arteries. At the extremity of the cord each of these vessels divide into an infinity of ramifications, which extend between two membranes. They separate at equal distances from the common trunk; so that these ramifications are round and flat, and are called, when thus collected, the placenta. The external surface, which is applied against the matrix, is convex; the internal concave. The blood of the fœtus circulates in the cord, and in the placenta. The arteries of the cord spring from two large arteries of the fœtus, and carry the blood through the arterial ramifications of the placenta; from thence it passes into the venous branches which carry it into the umbilical vessels; these communicate with a vein of the fœtus, in which vessels it is received.

The concave surface of the placenta is clothed by the chorion; the convex is also covered by a kind of soft membrane, easily torn, which seems to be a continuation of the chorion, and the fœtus is included under the double coat of the chorion and the amnios. The form is globular, because the intervals between the membranes and the fœtus are filled with a transparent liquor. This liquor is contained by the amnios, which is the internal membrane, it is thin and transparent; it folds round the umbilical cord at its insertion into the placenta, and covers it the whole length to the navel of the fœtus. The chorion is the external membrane; it is thick and spongy, sprinkled with sanguinary vessels, and composed of many coats, the exterior of which covers the convex surface of the placenta. It follows the inequalities, and covers the papillæ, which spring from the placenta, and are received in the cavities found at the bottom of the matrix, called lacunæ. The fœtus adheres to the matrix by these insertions.

Some anatomists have thought that the human form had, like those of certain quadrupeds; a membrane called allantois, destined to receive the urine; and they have pretended to have found it between the chorion and the amnios, or in the middle of the placenta at the root of the umbilical cord, under the form of a very large bladder, in which the urine entered by a long pipe that composed part of the chord, and which opened on one side into the bladder, and on the other in this allantois membrane, being similar to the urachus in other animals. They owned, however, that it was not near so large in the human fœtus as in quadrupeds, but that it was divided into many tubes, so minute, that they could scarcely be perceived, and that the urine passed into their cavities.

The experience and observations of most anatomists are contrary to this supposed discovery. They admit there is a kind of ligament which adheres by one end to the external surface of the bottom of the bladder, and extends to the navel; but it becomes so delicate, on entering into the cord, as to be nearly reduced to nothing: in common this ligament is not hollow, and we can see no orifice at the bottom of the bladder.

The fœtus has no communication with the open air, and the experiments made upon the lungs prove they have never respired; for they sink to the bottom when put in water: whereas those of infants who have breathed always float on the top; the fœtus then does not respire in the womb, consequently it cannot form any sound by its voice; and therefore what has been related of the groaning and crying of children before their birth may be considered as fables. After the flowing of the waters it may happen, that the air has found an entrance into the cavity of the matrix, and then the infant may begin to respire before it is brought forth. In this case it may be able to cry, as the chicken cries before the shell of the egg is broken, which it can do from there being air in the cavity which is between the external membrane and the shell. This air is found in all eggs, and is produced by the internal fermentation of matters contained in them[AF].

The lungs of the fœtus being without any motion, have no more blood enter into them than is requisite to nourish and make them grow; and there is another road opened for the course of its circulation. The blood in the right auricle of the heart, instead of passing into the pulmonary artery, and returning, after having ran through the lungs into the left auricle by the pulmonary vein, passes immediately into the left by an opening, called the foramen ovale, which is in the partition of the heart between the two auricles. It enters afterwards into the aorta, which distributes it by its ramifications, at going out of which the venous branches receive it, and bring it back to the heart by uniting all in the vena cava, which terminates at the right auricle of the heart. The blood which this auricle contains, instead of passing entirely by the foramen ovale, may escape in part into the pulmonary and the aorta by an arterial canal, which goes immediately from the one to the other. It is by these roads that the blood of the fœtus circulates without entering into the lungs, as it enters into those of children, adults, and every animal which breathes.

It has been thought that the blood of the mother passes into the body of the fœtus, by means of the placenta and umbilical cord. It was supposed that the sanguinary vessels of the matrix opened into the vacuities, and those of the placenta into the nipples, and that they joined one to the other; but experience is quite contrary to this opinion; for if the arteries of the umbilical cord is injected the liquor returns by the veins, and not any part of it escapes externally. Besides, the nipples may be drawn from the vacuities where they are lodged, without any blood issuing either from the matrix or placenta: a milky liquor only issues from both, and which, we have already observed, serves the fœtus for nutriment. This liquor possibly enters into the veins of the placenta, as the chyle enters into the subclavian vein; and perhaps the placenta in a great measure performs the office of the lungs in bringing the blood to maturity. It is certain that the blood appears much sooner in the placenta than in the fœtus, and I have often observed in eggs that have been under the hen for a day or two, that the blood appeared at first in the membranes, and that their sanguinary vessels are very large and numerous, while the whole body of the chicken, excepting the point where these blood-vessels terminate, is only a white and almost transparent matter, in which there is not the smallest sign of a sanguinary vessel.

It has been imagined, that the liquor of the amnios is a nutriment the fœtus receives by its mouth. Some naturalists pretend to have observed this liquor in the stomach, and to have seen some fœtuses to which the umbilical cord was entirely wanting, and others who had but a very small portion, which did not at, all adhere to the placenta; but in this case might not the liquor have entered into the body of the fœtus by the small portion of the umbilical cord, or by the umbilical vessel itself? Besides, to these observations we may oppose others. Some fœtuses have been found whose lips were not separated, and others without any opening in the œsophagus. To conciliate these circumstances, some anatomists have thought that the aliments passed into the fœtus partly by the umbilical cord, and partly by the mouth: none of these opinions appear to have any foundation. It is not the question to examine the growth of the fœtus alone, and to seek from whence and by what it draws its nutriment, but how the growth of the whole is made; for the placenta, liquor, and membrane increase in size as well as in the fœtus; and consequently the instruments and canals employed to receive or carry this nutriment to the fœtus, have a kind of life themselves. The expansion of the placenta and membranes is as difficult to conceive as that of the fœtus; and we might say, with equal propriety, that the fœtus nourishes the placenta, as that the placenta nourishes the fœtus. The whole mass is floating in the matrix, and without any adherence at the commencement of this growth: therefore the nourishment can be only made by an absorption of the milky matter contained in the matrix. The placenta appears first to draw this nutriment, to convert this milk into blood, and to carry it to the fœtus by veins. The liquor of the amnios appears to be only this milky liquor depurated, the quantity of which increases by a like absorption, proportionate to the increase of the membranes, and the fœtus probably absorbs the liquor, which appears to be the necessary nutriment for its expansion. For we must observe, that for the first two or three months the fœtus contains very little blood; it is as white as ivory, and appears to be composed of lymph which has taken some solidity; and as the skin is transparent, and all the parts very soft, we may easily conceive that the liquor in which the fœtus swims may penetrate them, and thus furnish the necessary matter for its nutrition and expansion. It may be supposed that the fœtus in the latter stages takes its nutriment by the mouth, since in the stomach we find a liquor similar to that in the amnios, urine in the bladder, and excrements in the intestines; and as we find neither urine nor meconium in the amnios, there is reason to conclude that the fœtus does not void its excrements, especially as some are born without having the anus pierced, although they had a great quantity of meconium in the intestines.

Although the fœtus does not immediately adhere to the matrix, but is only attached to it by small external nipples, though it has no communication with the blood of its mother, but is as independant of her who bears it, in many respects, as the egg is of the hen that hatches it, yet it has been pretended, that all which affects the mother affects the fœtus; that the impressions of the one act on the brain of the other; and to this imaginary influence resemblances, monsters, and especially marks on the skin of some children, have been attributed. I have examined many of these marks, and they all appear to me to have been caused by a derangement in the texture of the skin. Every mark must have a figure which will resemble something or other; but I am certain the resemblances so formed depend rather on the imagination of those who see them than on that of the mother. On this subject the marvellous has been carried as far as it could go. It has not been only said that the fœtus carried real representations of the longings of its mother, but that, by a singular sympathy, the marks, which represent strawberries, cherries, &c. change their colour, and become deeper in the season of those fruits. With a little more consideration, and less prejudice, this colour may be seen to change much oftener, and that it must happen every time the motion of the blood is accelerated, whether by the heat of summer or from any other cause. These marks are either yellow, red, or black, because the blood gives these tints to the skin when it enters in too great quantities into the vessels. If these marks have the longings of the mother for their cause, why have they not the forms and colours as varied as the objects of her desires? What a curious assemblage of figures would be seen if all the whimsical desires of the mother were written on the skin of the child?

As our sensations have no resemblance to the objects which cause them, it is impossible that desire, fear, horror, or any passion, or internal emotion, can produce real representations of those objects; and the child being in this respect as independant of the mother as the egg is of the hen, I should as soon believe that a hen, which saw the neck of a cock twisted, would hatch chickens with wry necks, as that, by the power of imagination, a woman, who happened to see a man broke upon the wheel, would bring forth a child with its limbs broken in the same manner.

But even supposing this circumstance attested, I should still support the opinion, that the imagination of the mother had not been the cause, for what is the effect of horror? an internal motion, a convulsion in the body of the mother, which might shake, compress, and agitate the womb. What can result from this commotion? nothing similar to the cause, for if this commotion was very violent the fœtus might be killed, wounded, or deformed in some of its parts; but how is it to be conceived that this commotion can produce any thing resembling the fancy of the mother in the fœtus, unless we believe, with Harvey, that the matrix has the faculty of conceiving ideas, and realizing them on the fœtus?

But, it may be urged, if it was not affected by the imagination of the mother, why did the child come into the world with broken limbs? However rash it may appear to explain a matter which is extraordinary and uncertain, and of which we have no right to exact a solution, yet this question appears to me answerable in a satisfactory manner. Circumstances of the most rare and extraordinary kind happen as necessarily as those which are frequent and common. In the infinite combinations which matter can take, the most extraordinary arrangements must sometimes happen; hence we might venture to wager, that in a million, or a thousand millions of children, there will be one born with two heads, four legs, or with broken limbs; it may, therefore, naturally happen, without the concurrence of the mother's imagination, that a child should be born with broken limbs. This may have happened more than once, and the mother, while pregnant, might have been present at the breaking on the wheel, and therefore the defect of the child's formation has been attributed to what she had seen, and to her impressed imagination. But, independant of this general answer, we may give a more direct explanation. The fœtus, as we have said, has nothing in common with the mother; its functions, organs, blood, &c. are all particular, and belong to itself; the only thing which it derives from its mother is the liquor, or nutritive lymph, which filtrates from the matrix. If this lymph is bad, or envenomed with the venereal virus, the child will be alike disordered; and it may be imagined, that all the diseases which proceed from vitiated humours may be communicated from the mother to the child. We know that the small-pox is communicative, and we have but too many examples of children who are, directly after their birth, the victims of the debauches of their parents. The venereal virus attacks the most solid parts of the bones, and it appears to act with more force towards the middle of the bone, where ossification commences; I conceive, therefore, that the child here spoken of has been attacked by the venereal disorder while in its mother's womb, and from that cause it came into the world with its bones broken through the middle.

Rickets may also produce the same effect. There is a skeleton of a rickety child in the French king's cabinet, whose arms and legs have callosities in the middle of their bones. By the inspection of this skeleton, it appeared evident that the bones had been broken during the time it was in the womb, and that afterwards the bones re-united, and formed these callosities.

But enough of a subject which credulity alone has rendered marvellous. Prejudice, especially that sort which is founded on the marvellous, will always triumph over reason, and we should have but little philosophy if we were astonished at it. We must not therefore ever expect to be able to persuade women, that the marks on their children have no connection with their unsatisfied longings. Yet might it not be asked them, before the birth of the child, of what particular longings they had been disappointed, and consequently what will be the marks their children will bear? I have often asked this question, and have only made persons angry without having ever convinced them.

The time that a woman goes with child is generally about nine months; but it is however sometimes longer and sometimes shorter. Many children are born at seven or eight months, and some not till after the ninth; but in general the deliveries which precede the term of nine months are more frequent than the others. The common time of a natural delivery extends to twenty days, that is, from eight months fourteen days to nine months and four hours.

Many children are born before the 260th day, and although these deliveries precede the general term, they are not abortions, because these children mostly live. It is commonly thought that children born at eight months cannot live, or at least that many more of them die than those born at seven months. This opinion appears to be a paradox; and by consulting experience I think we shall find it an error. The child brought forth at eight months is more formed, and consequently more vigorous, and likely to live than that which is born at the seventh. Nevertheless this opinion is pretty generally received, and founded on the authority of Aristotle.

The beginning of the seventh month is the earliest term for delivery; if the fœtus is brought forth sooner it dies, and is termed an abortion. There are, however, great limits for the time of human delivery, since they extend from the seventh to the tenth, and perhaps to the eleventh month.

Women who have had many children assert, that girls remain longer in the womb than boys. If this is really the case, we must not be surprized at female children being born at ten months. When children come before nine months they are not so well proportioned as those who are not brought into the world till ten months, the bodies of the latter are sensibly larger and better formed; their hair is longer, the growth of the teeth, although still hid under the gums, is more advanced; the voice is clearer, and the tone more deep.

There is much uncertainty on the occasional causes of delivery, and we do not perfectly know what obliges the infant to quit the womb. Some imagine, that the fœtus having acquired a certain size, the matrix is too confined for its longer stay, and that the constraint felt by the fœtus, obliges it to use every effort to quit its prison; others say, and it is nearly to the same purport, that the weight of the fœtus becomes so great, that the matrix is forced to open to free itself from the burthen. These reasons do not appear satisfactory; for the matrix must always have capacity and strength to contain and sustain the weight of a fœtus of nine months, since it often contains two, and it is certain that the weight and size of the twins of eight months are more considerable than the weight and size of a single child of nine. Besides, it often happens that a child born at nine months is smaller than the fœtus of eight months, although it continues in the womb.

Galen pretends, that the child remains in the matrix till it is able to receive its food by the mouth, and that it only forces its escape from the need of nutriment. Others have said, that the fœtus always receives its nourishment by the mouth from the liquor of the amnios; but which becomes at length so contaminated, by the transpiration and urine of the fœtus, that it becomes disgustful, and obliges the fœtus to use every exertion to quit its confinement. These reasons do not appear better than the first; for it would from thence follow, that the weakest and smallest fœtuses would remain longer in the womb than the strongest and largest, which never happens; besides, it is not food that the fœtus seeks immediately after it is born, for it can stay some time without it; on the contrary, it seems most desirous to disembarrass itself from the nutriment it took when in the womb of its mother, and to return the meconium. Other anatomists have supposed that the excrement accumulated in the bowels of the fœtus, gives it great pain, and causes it to make such efforts, that the matrix is at length obliged to give way, and to open a passage for its escape. I acknowledge I am not better satisfied with this explanation than the rest; because, why cannot the fœtus void its excrements in the amnios, if it was pressed so to do? Now this never happens; it appears, on the contrary, that this necessity of voiding the meconium is not felt till after the birth, when the motion of the diaphragm, occasioned by that of the lungs, compresses the intestines and causes this evacuation; for the meconium has never been found in the amnios of a fœtus of ten months who had not respired, whereas a fœtus of six or seven months voids this meconium a short time after respiration.

Other anatomists, and among them Fabricius de Aquapendente, have supposed the fœtus quitted the matrix through the need of procuring refreshment by means of respiration. This cause appears to me still more remote than all the rest, because the fœtus can have no idea of respiration without having respired.

After having weighed all these explanations, I suppose the fœtus's quitting the matrix depends on a quite different cause. The flowing of the menstrua is periodical, and at determined intervals; and although conception suppresses its appearance, it does not destroy the cause; for notwithstanding the blood does not appear at the accustomed times, yet a kind of revolution takes place, like that which is made before conception. Thus it is, there are many women whose menstrua are not suppressed in the first two or three months. I imagine, therefore, that when a woman has conceived, the periodical revolution is made as regular as before; but as the matrix is swelled, the excretory canals cannot give issue to the blood, at least unless it arrives there with such force, and in such quantities, as to open a passage in spite of the resistance, that is opposed to it. In this case blood will appear, and if it flows in a great quantity abortion will ensue, and the matrix take the form it had before. But if the blood only forces one part of these canals, the business of generation will not be destroyed, although the blood appears, because the greatest part of the matrix still remains in the state which is necessary for that purpose.

When no blood appears, as is generally the case, the first periodical revolution is remarkable and felt by the same pains and symptoms. From the first suppression of the menses, therefore, a violent action on the matrix is made, and provided the action is augmented, it destroys the product of generation. It may from thence be concluded, that every conception which is made just before the useful return of the menses seldom succeeds, and that the action of that blood easily destroys the weak roots of a germ so tender and so delicate. The conceptions, on the contrary, which are made just after the periodical evacuations succeed the best, because the produce of the conception has more time to grow, strengthen, and resist the action of the blood, by the time the next revolution happens.

The fœtus having undergone this first trial, and having resisted it, receives more strength and growth, and is more in a condition to contend against the succeeding revolutions. Miscarriages may and do happen in all the periodical revolutions; but they are less frequent in the fourth and fifth months, than either at the beginning or near the end. We have assigned the reasons why they are more frequent at the beginning; it therefore only remains to explain why they are also more frequent towards the end.

The fœtus generally comes into the world during the tenth revolution. When it is born at the eighth or ninth it lives, and these deliveries are not looked upon as miscarriages, because the child, although not so perfectly formed, is still sufficiently so for the purpose of life. It has been pretended, that examples have been seen of children born at the seventh and even at the sixth revolution, that is, at five or six months, which have lived. There is, therefore, no difference between a birth and a miscarriage but what is relative to the living powers of the infant. In general the number of miscarriages in the first, second, and third months are very considerable for the reasons we have given ; and the number of deliveries of the seventh and eighth months are also very great, in comparison with the miscarriages of the fourth, fifth, and sixth months, because in this middle period the product of generation has received more solidity and strength, and having resisted the action of the four first periodical revolutions, a more violent force than the preceding is required to destroy it. The same reason subsists, with additional force, for the fifth and sixth months. But the fœtus, which till then is weak, and can act only by its own feeble strength, begins to get strong, and move with vigour; and at the eighth revolution the fœtus, uniting its efforts with those of the matrix, facilitates its exclusion, and it may come into the world in the seventh month, and be capable of living, especially if it happens, as is sometimes the case, to have more than ordinary strength for that period. But if it comes into the world only through the weakness of the matrix, which could not resist the action of the blood in this eighth revolution, the delivery would be regarded as a miscarriage, and the child would not live. But these cases are very rare, for if the fœtus has resisted the seven first revolutions, only particular accidents can prevent it from resisting the eighth. The fœtus, which has acquired this same degree of strength and vigour only a little later, will come into the world at the ninth revolution; and those which require nine months to obtain this same strength, will come at the tenth revolution, which is the most common and general term; but when the fœtus has not acquired in nine months this degree of perfection, it may remain in the womb till the eleventh, and even till the twelfth revolution; that is, till the tenth or eleventh month, as we have many examples.

This opinion, that it is the menstrua which is the occasional cause of delivery at different times, may be confirmed by many other reasons. The females of every animal which have no menses, bring forth at nearly the same terms, and there is but a very slight variation in the duration of their gestation. We may, therefore, suppose that this variation, which is so great in women, comes from the action of the menstrual blood, which is constantly exerted at every periodic return.

We have observed, that the placenta adheres to the papillæ, or the matrix, only by nipples; that there is no blood either in these nipples or in the vacuities they are niched into, and that when they are separated (which is easily done) a milky liquor only issues from them. Now, how happens it that delivery is always accompanied with a considerable hæmorrhage, at first of pure blood, and afterwards mixed with a watery liquor? This blood does not proceed from the separation of the placenta, as the nipples are drawn out without any effusion of blood. Delivery, which entirely consists, of this separation, should not, therefore, produce any blood. Is it not then more accordant with reason to suppose, that it is the action of the blood which causes delivery, and that it is this menstrual blood which forces the vessels as soon as the matrix is emptied, and which begins to flow immediately after delivery as it did before conception?

It is known, that in the first months of pregnancy that which contains the seed of generation is not adherent to the matrix. By the experiments of De Graaf it has been seen, that by blowing on the little ball we can make it move. The adhesion to the matrix is never very strong, and at first the placenta with difficulty adheres to the internal membrane of the viscera, and those parts are only contiguous, or joined by a mucilaginous matter, which has scarcely any adhesion. Why then does it occur, that in miscarriages of the first and second month this ball never escapes without a great effusion of blood? It is certainly not caused by the passage of the ball quitting the matrix, since it does not adhere to it; but it is, on the contrary, by the action of this blood that the ball is driven out. Must we not then conclude this blood to be menstrual, which by forcing the canals, through which it had been accustomed to pass before impregnation, destroys the product of conception by retaking its common road?

It appears, therefore, that the periodical revolution of the menstrual blood has great influence on delivery, and that it is the cause why the times of delivery in women vary so much more than in every other female who is not subject to the periodical evacuation, and which always bring forth at the same times. It also appears that this revolution, occasioned by the action of the menstrual blood, is not the sole cause of birth, but that the action of the fœtus itself contributes towards it, since there are instances of a child escaping from the womb after the death of the mother, which necessarily supposes an action proper and particular in itself.

The space of time which cows, sheep, and other animals go with young is always the same, and their deliveries are not attended with an hæmorrhage. May we not then conclude, that the blood voided by women after delivery is the menstrual blood, and that the human fœtus being born at such different terms, can only be by the actions of this blood on the matrix during every periodical revolution? It is natural to imagine, that if the females of viviparous animals had menses like women, their deliveries would be followed with an effusion of blood, and happen at different terms. The fœtuses of animals come into the world clothed with their membranes (and it seldom happens that the membranes are broken), and the waters flow before the delivery; whereas it is very rare a child is brought forth with its membranes entire. This seems to prove that the human fœtus makes more efforts than other animals to quit its prison; or that the matrix of a woman does not so naturally incline to the passage of the child, for it is the fœtus which tears its membranes, by the efforts it makes against the resistance it meets with at the orifice of the viscera.

RECAPITULATION.

All animals procure nutriment from vegetables, or other animals which feed upon vegetables; there is, therefore, one common matter to both, which serves for the nutrition and expansion bf every thing which lives or vegetates. This matter cannot perform them but by assimilating itself to each part of the animal or vegetable, and by intimately penetrating the texture and form of these parts, which I have called the internal mould. When this nutritive matter is more abundant than is necessary to nourish and expand the animal or vegetable, it is sent back from every part of the body, and deposited in one or more reservoirs, in the form of a liquor; this liquor contains all the molecules analogous to all parts of the body; and consequently all that is necessary for the reproduction of a young being, perfectly resembling the first. Commonly this nutritive matter does not become superabundant, in most kinds of animals, till they have acquired the greatest part of their growth; and it is for this reason that animals are not in a state of engendering before that time.

When this nutritive and productive matter, which is universally spread abroad, has passed through the internal mould of an animal or vegetable, and has found a proper matrix, it produces an animal or vegetable, of the same kind; but when it does not meet with a proper matrix, it produces organized beings different from animals and vegetables, as the moving and vegetating bodies seen in the seminal liquor of animals, in the infusion of the germ of plants, &c.

This productive matter is composed of organic particles, always active, the motion and action of which are fixed by the inanimate parts of matter in general, and particularly by oily and saline bodies, but as soon as they are disengaged from this foreign matter, they retake their action, and produce different kinds of vegetations and other animated, beings.

By the microscope, the effects of this productive matter may be perceived in the seminal liquors of animals of both sexes. The seed of the female viviparous animals is filtered through the glandular bodies which grow upon their testicles, and these glandular bodies contain a large quantity of seminal fluid in their internal cavities. Oviparous females have, as well as the viviparous, a seminal liquor, which is still more active than the viviparous. The seed of the female is in general like that of the male, when, they are both in a natural state: they decompose after the same manner, contain similar organic bodies, and they alike offer the same phenomena.

All animal or vegetable substances include a great quantity of this organic and productive matter. To perceive it, we need only separate the inanimate parts in which the active particles of this matter are engaged. And this is done by infusing animal or vegetable substances in water. The salts will dissolve, the oils separate, and the organic particles will be seen by their putting themselves in motion. They are in greater abundance in the seminal liquors than in any other parts, or rather, they are less entangled by the inanimate parts. In the beginning of this infusion, when the flesh is but slightly dissolved, the organic matter is seen under the form of moving bodies, which are almost as large as those of the seminal liquors: but, in proportion as the decomposition augments, these organnic particles diminish in size and increase in motion; and when the flesh is entirely decomposed, or corrupted, these same particles are exceedingly minute, and their motion exceedingly rapid. It is then that their matter may become a poison, like that of the tooth of a viper, wherein Mr. Mead perceived an infinite number of small pointed bodies, which he took for salts, although they are only these same organic particles in a state of great activity. The pus which issues from wounds abounds with little insects, and it may take such a degree of corruption as to become one of the most subtle poisons; for every time this active matter is exalted to a certain point, which may be known by the rapidity and minuteness of the moving bodies it contains, it will become a species of poison. It is the same with the poison of vegetables. The same matter which serves to feed us when in its natural state, will destroy us when corrupted. Spurred barley, for instance, throws the limbs of men and animals into a gangrene who feed on it. It is also evident by comparing the matter which adheres to our teeth, which is the residue of our food, with that from the teeth of a viper or mad dog, which is only the same matter too much exalted, and corrupted to the last degree.

When this organic and productive matter is found collected in a great quantity in some part of an animal, where it is obliged to remain, it forms living beings which have been ever regarded as animals; the tænia, ascarides, all the worms found in the veins, liver, in wounds, in corrupted flesh, and pus, have no other origin; the eels in paste, vinegar, and all the pretended microscopical animals are only different forms which this active matter takes of itself, according to circumstances, and which invariably tends to organization.

In all animal and vegetable substances, decomposed by infusion, this productive matter manifests itself immediately under the form of vegetation. Filaments are seen to form, which grow and extend like plants. Afterwards these extremities and knots swell and burst, to give passage to a multitude of bodies in motion, which appear to be animals; so that it seems as if all nature began by a motion of vegetation. It is seen by microscopical objects, and likewise by the expansion or unfolding of the animal embryo; for the fœtus at first has only a species of vegetable motion.

Sound food does not furnish any of these moving molecules for a considerable time. Several days infusion in water is required for fresh meat, grain, kernels, &c. before they offer to our sight any moving bodies; but the more matters are corrupted, decomposed, or exalted, the more suddenly these moving bodies manifest themselves; they are all free from other matters in seminal liquors; but a few hours infusion is required to see them in pus, spurred barley, honey, drugs, &c.

There exists therefore, an organic matter, universally diffused in all animal and vegetable substances, which alike serves for their nutrition, their growth, and their reproduction. Nutrition is performed by the intimate penetration of this matter in all parts of the animal or vegetable body. Expansion or growth is only a kind of more extended nutrition, which is made and performed as long as the parts have sufficient ductility to swell and extend; and reproduction is made by the same matter when it superabounds in the body of the animal or vegetable; each part of the body sends back, to the appropriate reservoirs, the organic particles which exceed what are sufficient for their nourishment. These particles are absolutely analogous to each part from which they are sent back, because they were destined to nourish those parts from hence, when all the particles sent back from, collect together, they must form a body similar to the first, since each particle is like that part from which it was detached; thus it is that reproduction is effected in all kinds of trees, plants, polypuses, pucerons, &c. where one individual can produce its like; and it is also the first mode which Nature uses for the reproduction of animals which have need of the communication of different sexes; for the seminal liquors of both sexes contain all the necessary molecules for reproduction; but something more is required for its effectual completion, which is the mixture of these two liquors in some places suitable to the expansion of the fœtus which must result therefrom, which place is the matrix of the female.

There are, therefore, no pre-existing germs, no germs contained one in the other, ad infinitum; but there is an organic matter perpetually active, and always ready to form, assimilate, and produce beings similar to those which receive it. Animals and vegetables, therefore, can never be extinct; so long as there subsist individuals the species will ever be new; they are the same at present as they were three thousand years ago, and will perpetually exist, by the powers they are endowed with, unless annihilated by the will of the Almighty Creator.

HISTORY OF MAN.

CHAPTER I.

OF THE NATURE OF MAN.

Though so much interested in acquiring a thorough knowledge of ourselves, yet I do not know if man is not less acquainted with the human, than with any other existence. Provided by nature with organs, calculated solely for our preservation, we only employ them to receive foreign impressions. Intent on multiplying the functions of our senses, and on enlarging the external bounds of our being, we rarely make use of that internal sense which reduces us to our true dimensions, and abstracts us from every other part of the creation. It is, however, by a cultivation of this sense alone that we can form a proper judgment of ourselves. But how shall we give it its full activity and extent? How shall the soul, in which it resides, be disengaged from all the illusions of the mind? We have lost the habit of employing this sense; it has remained inactive amidst the tumult of our corporeal sensations, and dried up by the heat of our passions; the heart, the mind, the senses, have all co-operated against it.

Unalterable in its substance, and invulnerable by its essence, it still, however, continues the same. Its splendor has been overcast, but its power has not been diminished: it may be less luminous, but its guidance is not the less certain. Let us then collect those rays, of which we are not yet deprived, and its obscurity will decrease; and though the road may not in every part be equally filled with light, we yet shall have a torch that will prevent us from going astray.

The first and most difficult step which leads to the knowledge of ourselves, is a distinct conception of the two substances that constitute our being. To say simply, that the one is unextended, immaterial, and immortal, and that the other is extended, material, and mortal, is only to deny to the one, what we affirm the other possesses. What knowledge is to be acquired from this mode of negation? Such negative expressions can exhibit no positive ideas: but to say that we are certain of the existence of the former, and that of the latter is less evident; that the substance of the one is simple, indivisible, and has no form, since it only manifests itself by a single modification, which is thought; that the other is a less substance than a subject, capable of receiving different forms, which bear a relation to our senses, but are all as uncertain and variable as the organs themselves; that is to say something; it is to ascribe to each such distinct and positive properties as may lead us to an elemental knowledge of both, and to a comparison between them.

From the smallest reflection on the origin of our knowledge, it is easy to perceive that it is by comparison alone we acquire it. What is absolutely incomparable, is utterly incomprehensible; of this God is the only example; he exceeds all comprehension, because he is above all comparison. But whatever is capable of being compared, contemplated, and considered relatively, in different lights, may always come within the sphere of our understanding. The more subjects of comparison we have for examining any object, the more methods there are for obtaining a knowledge of it, and with greater facility.