Page:Popular Science Monthly Volume 2.djvu/83

Rh secretes, production of heat invariably takes place at the same time with increased activity in the phenomena of local circulation.

Is the case the same with the nervous system and the brain? Modern experiments forbid us to doubt it. Whenever the spinal marrow and the nerves exhibit sensibility or movement, whenever an intellectual effort takes place in the brain, a corresponding quantity of heat is evolved in it. We must, then, regard heat in the animal economy as a resultant of the organic labor of all the parts of the body; but at the same time it becomes also the principle of activity for each of these parts. This correlation is, above all, indispensable for the brain and the nervous system, which hold all the other vital actions under their control. Experiments have demonstrated that the tissue of the brain exhibits a higher temperature than any other organ of the body. In man and the warm-blooded animals the brain itself produces the heat required for the manifestation of the peculiarities of its tissue. If this were not so, it would infallibly grow cooler, and we should at once see all the functions of the brain become torpid, and intelligence and will perish. This does, in fact, occur in cold-blooded animals, in which the function of heat-production is not energetic enough to sustain the organism in resistance to external causes of refrigeration.

With respect to the organic or physico-chemical conditions of its activity, the brain, then, presents nothing exceptional. If we turn to experiments made upon it by physiologists, we shall find that they have succeeded in analyzing cerebral phenomena in the same way as those of all the other organs. The experimental process usually employed to determine the functions of organs consists in removing them or in destroying them either gradually or suddenly, so as to determine the uses of the organ according to the special disturbances thus caused in vital phenomena. This method of the removal or destruction of organs, which forms a sort of brutal vivisection, has been applied on a great scale to the study of the whole nervous system. Thus, after a nerve is cut, when the parts to which it had been distributed lose their sensibility, we conclude from this that it is one of the nerves of sensation; if it is motion that ceases, we infer thence that we are dealing with one of the nerves of motion. The same method has been applied in examining the functions of the different parts of the encephalic organ, and, though the complexity of the parts has occasioned novel difficulties of execution, the method has yielded results that are not to be contested. Every one has long known that, without the brain, intelligence is not possible, but experiment has discovered exactly the part that is played by each portion of the organ. It teaches us that consciousness, or intelligence properly so called, resides in the cerebral lobes, while the lower portions of the brain contain nervous centres destined