Page:Popular Science Monthly Volume 11.djvu/347

Rh It has been discovered that when a branch of that nervous system is sectioned, is separated from its centre, the blood-vessel with which it is connected almost at once enlarges: its calibre increases, more blood passes through it during a given time, etc. But if, now, this separated end of the nerve is irritated, the reverse phenomena are seen: the blood-vessel contracts, its calibre diminishes. When small arteries are experimented upon, the calibre becomes so small that blood-corpuscles no longer succeed in passing through it. So that it becomes evident that that nervous system has a great function to perform with regard to the nutrition of all the parts, or rather of every organ in the body, including, of course, the central, i. e., the spinocerebral nervous system, for the "blood is the life of the anatomical elements." The materials which compose animal bodies are endowed with properties which differ in every different tissue: for instance, we say that the muscular tissue has the property of contracting. These properties of tissues develop functions: for example, the contraction of the ciliary muscle permits correct vision; but it is evident that if the tissue does not keep up the process of nutrition, i. e., assimilation and disassimilation, which it can only do by the agency of the blood which carries to it new materials, and removes effete elements, its properties are impaired and its functions are consequently perverted. This point being understood, I proceed to relate the experiments:

If in a Guinea-pig, for instance, that portion of the vaso-motor branch which is in connection with the carotid artery in the neck,—which, therefore, regulates the blood-supply of some part of the brain, of the ear, of the face, and of the eye—be divided, or, better still, if the ganglion from which that branch springs be removed, we see that the entire half of the head of the animal, on the side on which the operation has been performed, becomes hotter, and on examining more closely we discover that the increase of heat is due to the fact that the blood-vessels allow more blood to pass through them, that the nutrition of the parts is increased, and therefore the heat also increases; and we see that the upper eyelid of the animal drops a little, being in a state of hyperæmia—that is, its capillaries are distended—that the secretion of tears is increased so that the eye is wet, that the pupil of the eye is contracted because of more blood in the ciliary system, etc. The ear also becomes hotter, and, if the animal is white, we can see that the ear which before was white, with some blood-vessels stretching across, is now become red, and presents a very rich network of capillaries, which have become apparent, being of enlarged calibre.

Now, all these phenomena may disappear after a while, except a few. The eye always remains smaller, although the blood-supply of the eyelid is more regulated; the pupil remains a little contracted, and the secretion of tears continues, and also the nictitantnictating [sic] membrane remains in a congested state. No matter how long the animal lives,