CONCLUSIONS 107 



^Concerning the nature of the material basis of the 

 nerve impulse we can only say that it appears to involve 

 that part of the chemical transformations in protoplasm 

 which result in the production of carbon dioxide. 

 Farther than this we cannot go at present. But it is 

 certain that it has a chemical basis. Whether it has also 

 a physical basis, such as a change in state of the colloidal 

 substratum of the nerve, or not, we cannot yet say. 

 Who shall write the chemical reaction of the future, 

 embracing, not only the energy exchange, but the change 

 in psychism as well ? 



Finally, we come to the quantity of life, the point 

 from which we started. The measure of this is the 

 amount of respiration, or the amount of electrical 

 response shown on stimulation. The question of how 

 much we are alive must be answered by the determina- 

 tion of the extent to which we are undergoing energy 

 transformation. Death and peace, life and struggle 

 these are the pairs which go together. The most perfect 

 young life is that which shows the highest metabolic 

 rate. We have shown the general correlation between 

 the carbon dioxide production and the nerve impulse 

 in its speed of propagation and ease of origin. There 

 must, then, be a close correspondence between the habit 

 of the organism and the general metabolic rate. The 

 simile of the torch is obvious. The faster it burns the 

 more light and life it has. The most vigorous life is 

 that with the keenest chemical change. And this is also, 

 as has been shown in another volume in this series, the 

 criterion of youth. The most successful life is that in 

 which the nervous system remains active, youthful, and 

 alive for the greatest number of years. It is the youth- 



