Note 110 — Chapter X · OF THE INFLUENCE OF THE DEATH OF THE BRAIN OVER THAT OF THE LUNGS.
F. Gold translation
The division of the nerves of the eighth pair in the neck produces two kinds of effects, which should be carefully distinguished; the one relates to the larynx and the other to the lungs. Among the first, aphonia is one of the most striking symptoms. We see a very good reason for this phenomenon, when we recollect that the recurrent nerve is a branch of the eighth pair; but besides the loss of voice, the division of the eighth pair often produces such an approximation of the edges of the glottis that the air cannot enter, and death immediately takes place.
Most usually, the approximation is not sufficient to prevent entirely the entrance of the air into the thorax; but as the glottis has lost its motions in relation with those of respiration, this function is always performed in a more or less incomplete manner.
When these observations were first made, it was hardly possible to give an accurate explanation of them; but since I have ascertained the manner in which the recurrent and laryngeal nerves are distributed to the muscles of the larynx, there is no longer any difficulty. By the division of the eighth pair at the inferior part of the neck, the dilator muscles of the glottis are paralyzed; this opening does not enlarge at the moment of inspiration, whilst the constrictors, which receive their nerves from the superior laryngeal, preserve their action entire, and shut more or less completely the glottis.
When the division of the eighth pair does not close the glottis so completely as to produce death immediately, another order of phenomena is developed.
The respiration is at first embarrassed, and its rhythm often experiences a remarkable alteration; the inspiration is slow, and the expiration quick and short. The animal is averse to motion and seems to be easily fatigued. At first the formation of the arterial blood is not prevented, but soon its vermilion colour changes, it becomes darker and approximates more and more that of the venous blood. The temperature falls, and the very embarrassed respiration is only made by the aid of all the muscular powers; the coldness becomes evident, and the animal soon dies.
As this series of circumstances is developing, the animals, on whom the experiments are made, consume less oxygen, and form less carbonic acid.
We find, on opening the body, the bronchia filled with a frothy, and sometimes a bloody fluid; the lungs are engorged, and the divisions of the pulmonary artery are much distended with very black blood.
From all that has now been stated, it is natural to conclude that, in this last case, the animals die because respiration can no longer be effected, the lungs being so altered that the air cannot get into the bronchial cells. To this cause should be added also the difficulty which the blood experiences in passing from the arteries to the pulmonary veins.