344 POPULAR SCIENCE MONTHLY. 



we suppose all the processes of nutrition and decay, secretion, as- 

 similation, 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 de- 

 stroyed the muscles waste away. Dr. Darkschwitsch has recent- 

 ly published in the Archiv fur Psychiatrie an elaborate study of 

 certain forms of muscular atrophy complicated with painful dis- 

 ease of the joints. These frequently follow paralyses due to in- 

 jury 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 pa- 

 tient 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 conse- 

 quence, 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 vaso- 

 motor mechanism which controls the force and rate of the heart- 

 beat 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 renexly, 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 metabo- 

 lism, but they do not show how those processes can be affected by 

 the functioning of that part of the nervous system which under- 

 lies 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 pro- 

 cesses can not only often be started and stopped in this way, but 

 the chemical character of their products can be modified, as when 



