Herrick, Physiology of the Nervous Elements. 141 



pect that there should be a longer or shorter period of 

 such cell-multiplication after which the wear and tear of 

 nervous activity might gradually increase over the process 

 of multiplication ; for we must assume that nerve cells, like 

 all other active tissue elements, wear out in activity. 



The writer has given some time to the study of this 

 question and finds evidence that certain portions of the 

 proliferating epithelium persist to a very late period and 

 continue the process of cell-formation. In other words 

 centres are established whence are derived fresh cells to 

 supply the place of such as become vitiated or depau- 

 perate. 



It is a problem of great moment to determine how 

 long and to what extent this process may continue, and 

 what conditions may accelerate or retard the proliferation 

 of new nerve cells. 



There is probably no morphological study more fas- 

 cinating and suggestive than the tracing of the marvelous- 

 ly intricate foldings and plications and invaginations and 

 local thickenings which transform the embryonic nerve 

 tube into the complicated structure known as the brain; 

 but hand in hand with this study and of vastly greater 

 practical import is the tracing of the development, migra- 

 tions, and successive modifications of the cells which, 

 although they all originate from the ventricular aspect ot 

 the tube, weave themselves into the intricate fabric of the 

 brain. 



In particular we may refer to the cerebellum as an 

 organ quite devoid of psychical significance but profoundly 

 important as the great supplementary reservoir of nervous 

 energy which backs up the feeble mandates of the will by 

 the sanctions of explosive nerve matter sufficient to wing 

 the arrow of a Tell or guide the sling of a David. 



The cerebellum, although an apparently massive 

 organ second in size among the major divisions of the 



