Page:Popular Science Monthly Volume 49.djvu/362

344 we suppose all the processes of nutrition and decay, secretion, assimilation, excretion, oxidation, etc., to be at bottom alike, and in the last analysis to consist in an exchange or substitution of atom for atom within the constituent molecules of the body.

Now, it is easily shown that this notion is erroneous, for the physical and chemical processes taking place within the body are not precisely like other such processes; they stand to some extent under the control of the nervous system. For example, the amount of heat evolved within the body is probably regulated by a center in the spinal cord. The nutrition of the voluntary muscles probably depends upon the functioning of certain cells in the anterior horns of the spinal cord, and if the latter are destroyed the muscles waste away. Dr. Darkschwitsch has recently published in the Archiv für Psychiatrie an elaborate study of certain forms of muscular atrophy complicated with painful disease of the joints. These frequently follow paralyses due to injury of the cortex, and he concludes that the metabolic changes probably result directly from the cortical injury and not from disuse of the affected limbs. I recollect seeing some time ago a patient of Dr. Charles K. Mills's who had had the left cortical center for the hand removed to cure an epilepsy. He had lost in consequence, as was to be expected, much of his power over the right arm and hand, and he had also lost, as was not to be expected, all the skin of his right hand. Dr. Mills told me he had several times seen localized metabolic disturbances follow lesion of that region of the cortex which controlled the muscles of the affected part.

Besides this probable direct control, the nervous system can affect metabolic processes indirectly through the blood supply. The distribution of the blood is regulated by the complex vasomotor mechanism which controls the force and rate of the heartbeat and the diameter of the arteries and arterioles; the entire system is controlled in turn by a center in the medulla. It acts for the most part reflexly, sending the blood tide with the greatest force to the organ that needs it most, but it can be affected in other ways.

Such facts are interesting, and they put it beyond question that the nervous system has to do with the processes of metabolism, but they do not show how those processes can be affected by the functioning of that part of the nervous system which underlies consciousness, or, to use my former phraseology, how mental states can control metabolism.

That some metabolic processes can be affected by mental states is well known. For example, the secretory and excretory processes can not only often be started and stopped in this way, but the chemical character of their products can be modified, as when