Herrick, Physiology of the Nervous Elements. 143 



Enough has been said to show that there are great 

 vital problems to be solved before the real significance of 

 the essential organs of the nervous system can be made 

 out. 



Now if the period of cell formation is at all dependent 

 on nutritive conditions we have a physiological explanation 

 of certain very important facts in education. It is well 

 known that exercise of brain functions promotes the flow 

 of blood to the organ. Such an increase in blood will 

 serve to modify the structure; it will also stimulate the 

 proliferation of new cells. It is entirely rational to claim 

 that an overdraft on this proliferating power may perman- 

 ently limit the sources from which the nervous supply 

 must subsequently be developed. 



A recent paper in the Hospital Ga:;cttc by J. A. 

 Diggle, M. D. gives concrete illustrations of this tendency. 

 On the other hand, such moderate activity of mind as shall 

 keep the centres nourished is essential to the normal cell- 

 multiplication necessary to the development of the organs. 

 It is an interesting problem also to trace the relation be- 

 tween such centres of multiplication and the processes of 

 senility. Wilks has said "a man is no younger than his 

 arteries." It is true that the sclerosed arteries, by being 

 less elastic, and as a result of the disappearance of their 

 muscles, become subject to hemorrhage which in the 

 brain, at least, is soon fatal ; but, as recently shown by Dr. 

 Grube, "the senile condition is essentially a general 

 atrophy." Inasmuch as atrophies are known to result 

 from imperfect innervation, it does not seem far-fetched to 

 claim that the source of senile degenerations may arise 

 from the diminution of nervous power which, in turn, may 

 be dependent on the exhaustion of the proliferating centres 

 of cell formation within the brain. It becomes, therefore, 

 a practical problem to discover what the conditions of 

 senility within the brain really are and to what extent 



