Meyer, Data of Modern Netirology. 277 



be found preserved in the adult and practically normal at the 

 autopsy, apart, perhaps, from the atrophy due to disuse and 

 from the characteristic alteration of the cell-body, the transitory, 

 so-called traumatic, reaction. Only in the young do we find 

 atrophy and even degeneration of the cell and remaining stump. 

 Descending degeneration is the term used for the decay of 

 fibers, the cells of origin of which are located 'above ' a lesion; 

 ascending degeneration a term used for the decay of fibers the 

 cells of which are located in segments ' behind ' a lesion. Such 

 a statement gives the facts and at the same time the problems, 

 and can be grasped by every man who deserves to be called a 

 medical student, if the proper illustrations and demonstrations 

 are furnished. 



We cannot leave this sketch of the best-known neurones 

 without a short statement concerning the changes observed in 

 them zVz normal and pat]iological conditions, ««(^ especially tJie in- 

 terrelation of the neurones and their zvays of interaction. 



For the neurone-theory the life-history of the elements is 

 of fundamental importance. The early stages of development 

 are well-known. It seems certain that a cell which has a spe- 

 cific process and is thus characterized as a nerve-cell, has lost its 

 power of reproduction, Karyokineses become rare after the 

 fifth month of gestation and the claim has been made that at 

 birth the entire stock of nerve-cells is present, later growth of 

 the nervous system meaning merely a growth of existing ele- 

 ments. The question is treated by Donaldson (Growth of the 

 Brain, p. 163- 171). Schiller's count of the fibers of the third 

 nerve in the young and adult cats and Kayser's counts of cells 

 in the cervical cord of the human foetus, child and man, show 

 a discrepancy. Schiller found the number of fibers remaining 

 the same. Kayser found an increase of developed cells up to 

 adult life. It is probable that the discrepancy is only apparent; 

 because we do not know how many undeveloped cells Kayser 

 started with. From the presence of centrosomes found in a few 

 cells (Lewis, Lenhossek, Dehler, etc.) no conclusion should be 

 drawn now; the occasional karyokinesis not only of neuroglia 



