Herrick, Corollaries of Neurological Discoveries. 157 



cognitive elements are awakened in response to changes rather 

 than invariable or monotonous stimuli. This conception is not 

 at all opposed to a very complete localization of function, while 

 it nevertheless also applies to the numerous cases of substitu- 

 tional or vicarious function. It also explains the fact that the 

 loss of a considerable amount of brain substance, in particular 

 within the cortex, is followed by a degradation of the totality 

 of the conscious power. 



Neural Interpolation. An interesting corollary of the above 

 theory affords an explanation of the phenomena of reproduc- 

 tion. It is a fact which can no longer be doubted that in a 

 number of places in the central nervous system there are formed 

 temporary or permanent clusters of cells whose function it is to 

 proliferate in later periods and thus take the place of the origi- 

 al germinative areas of ventricular epithelium. An interesting 

 analogy exists between this process and the method by which 

 the continual formation of blood corpuscles in later life is pro- 

 vided for. The primitive process of transforming the haemato- 

 blasts into the definitive corpuscles in various parts of the body 

 becomes progressively restricted by the differentiation of the 

 exposed parts until it is only in a few remnants of the prolifer- 

 ating substrate, as in the red marrow and the so-called blood 

 glands, that the proliferation is usually to be detected. In like 

 manner the original power, common to the embryonic ventric- 

 ular epithelium throughout its entire extent, of proliferating 

 new neuroblasts is gradually destroyed by the differentiation of 

 the definitive epithelial Hning of the ventricles and the prolifer- 

 ating power is inherited by such special outgrowths from the 

 primitive epithelium as have in the mean time lodged them- 

 selves in localities suited to their function of perpetuating the 

 structure of the organ and preserving the power of plastic re- 

 pair and neural substitution. Professor His first showed how 

 such a process is possible by tracing the origin of the olives 

 and nuclei of the medulla. The writer followed with the de- 

 scription of the process in the cerebellum. It was shown in 

 the case of the cerebellum that the essential elements of this 

 massive organ are derived from the ventricular epithelium, to 



