Meyer, Data of Modern Neurology. 129 



conditions by Duval, on ground of the considerations of Rabl- 

 Riickhard and Weidersheim, who suggested the contractility of 

 nerve elements by means of which one cell can withdraw from 

 contact with another ; or by Ramon y Cajal who attributed to 

 the neuroglia an active role in the production of sleep and rest. 

 In these conditions the neuroglia would separate the cells 

 from one another while, during activity, it would withdraw and 

 make contact possible. For the time being, these are reveries 

 which have been pleasantly or unpleasantly interrupted by 

 Held. They have really nothing to do with the fundamental 

 concepts of the neurone theory and will not occupy us any 

 longer here. 



We might however, look for danger in another quarter, 

 namely in the recent development of our knowledge of neuro- 

 glia, as presented by Weigert in his Beitrage ziir Kenntnis der 

 normalen mcnscJiliclicn Neiuvglia, i8g^. All the evidence of 

 histogenesis goes to prove that the neuroglia elements are of 

 ectodermal origin, and are derived from the same cells as the 

 nerve cells\ For a long time views identical with the general prin- 

 ciples of the neurone theory have been held with regard to the 

 neuroglia, even before the neurone theory existed, and by men 

 who deny its justification, such as Golgi. They (Fromann, 

 Golgi and others) claimed that the neuroglia consists only of 

 cells and their processes. Weigert admits this only for the 

 embryonic condition. " In the full grown state the neuroglia 

 consists of cells and moreover of fibers, and the latter prepon- 

 derate in such enormous proportion with regard to the space 

 taken up by them that they are to be considered the more im- 

 portant part of the ' neuroglia. ' These fibers are by no means 

 processes of cells, but fibers which are perfectly differentiated 

 from the protoplasm." 



We witness in this a peculiar difference in the develop- 

 ment of the fundamental conceptions concerning two sister 

 structures. The neuroglia having conquered a position in the 



^ See Alfred Schaper : Die friihesten Differenzirungs-vorgange im Central 

 nervensystems. Archiv flir Entwicklungsniechanik der Organismen V, pp. 

 Si-232. 



