Page:Popular Science Monthly Volume 2.djvu/79

From Wikisource
Jump to navigation Jump to search
This page has been validated.
67
ON THE FUNCTIONS OF THE BRAIN.

form. Every organ is in fact, then, an instrument whose constituent elements remain identical, while their grouping grows more and more involved in the same degree as the function itself displays more variety and complexity.

Reflecting, now, on the organic and physico-chemical conditions required for the support of life and the discharge of its functions, we find that they are the same in the brain as in all the other organs. The blood acts on the anatomical elements of all the tissues by supplying their indispensable conditions of nutrition, temperature, and humidity. When a diminished supply of blood flows to any organ, its activity of function declines, and the organ rests; but if the blood is quite cut off, the elementary properties of the tissue slowly change, while at the same time its function perishes. It is precisely the same as to the brain's anatomical elements: as soon as the blood ceases to flow to it, its nerve-properties are affected, as well as its function, which gradually disappears, if the blood remains wholly withheld. A simple modification of the temperature of the blood, in its pressure, is enough to produce grave disturbances in the sensibility, the power of motion, or the will.

All the bodily organs present alternate states of rest and of activity in which the phenomena of circulation differ essentially. Numerous observations, made upon the most different structures, place these facts beyond doubt. When, for instance, we examine the alimentary canal of a fasting animal, we find the mucous membrane that lines the inner face of the stomach and intestines, pale and but little supplied with blood; during digestion, on the contrary, we learn that the same membrane is highly colored, and swollen with the blood which flows energetically into it. These two phases of circulation, in a state of rest and a state of activity, have been brought under direct investigation in the stomach of a living man. All physiologists recollect the story of a young Canadian accidentally wounded by a leaden musket-ball which struck him almost point-blank on the left side. The abdominal cavity was laid open by an immense contused wound, and the stomach, extensively perforated, allowed the food which he had last taken, to escape. The patient was attended by Dr. Beaumont, a surgeon of the United States Army; he recovered, but retained a fistulous wound, opening with a circumference of about an inch and a half through which different substances could be introduced, and the action of the stomach easily examined. Dr. Beaumont, anxious to study this remarkable case, employed the young man as a servant, after the complete restoration of his health and particularly of his digestive powers. He was able to keep him in his service for seven years, during which he made a great number of observations of the highest interest to physiology. On looking into the interior of the stomach while empty of food, the lining membrane could be plainly seen, lying in uneven folds, with its surface of a pale rose-color, motionless, and lubricated by noth-