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.
[111] These words passion, emotion, affection, &c. have, I know, real differences in the language of metaphysicians; but as the general effect of the sensations which they express is always the same on the organic life; as this general effect is what alone concerns me, and as the secondary phenomena are of no importance, I use these words indifferently for each other.
[112] We have said in a preceding note, that the division of the nerves of the eighth pair could produce death in two ways; first, by closing the glottis, and preventing the entrance of the air into the air tubes; secondly, by altering the lungs and preventing the production of the chemical phenomena. Of these two kinds of death the first is in some measure accidental; it is an indirect effect of the interruption of the action of the brain; but it is not so with the second, and though it may not be instantaneous, it is not less a direct effect of the division. It might be supposed that the motions of the glottis being destroyed, and the entrance of the air being rendered consequently more difficult, that it is in consequence of this obstruction that respiration is embarrassed, and that the alteration of the lungs is only a consecutive phenomenon. But in the experiments made by M. Dupuy at Alfort, a free passage was given to the air, by an opening made in the trachea. Now it cannot be believed that the small wound necessary for this opening, could contribute to produce the disturbance of the respiration, for a similar operation is daily performed on horses, without producing the slightest inconvenience.
[113] The experiments of Legallois have clearly proved, that this point is at the origin of the nerves of the eighth pair.
[CHAPTER XI.]
OF THE INFLUENCE OF THE DEATH OF THE BRAIN OVER THAT OF THE HEART.
In the preceding chapter we have shewn how the lungs remain inactive, when the brain ceases to act.—The same phenomenon, under the same circumstances, takes place also in the heart, and must happen either immediately or mediately.