PROGRESS IN EXPERIMENTAL PSYCHOLOGY 



then came readily to repeat Cajal's experiments. So 

 also did the veteran histologist Kolliker, and soon after- 

 wards all the leaders everywhere. The result was a 

 practically unanimous confirmation of the Spanish his- 

 tologist's claims, and within a few months after his an- 

 nouncements the old theory of union of nerve cells into 

 an endless mesh-work was completely discarded, and 

 the theory of isolated nerve elements the theory of 

 neurons, as it came to be called was fully established 

 in its place. 



As to how these isolated- nerve cells functionate, Dr. 

 Cajal gave the clew from the very first, and his expla- 

 nation has met with universal approval. 



In the modified view, the nerve cell retains its old 

 position as the storehouse of nervous energy. Each of 

 the filaments jutting out from the cell is held, as before, 

 to be indeed a transmitter of impulses, but a transmit- 

 ter that operates intermittently, like a telephone wire 

 that is not always " connected," and, like that wire, the 

 nerve fibril operates by contact and not by continuity. 

 Under proper stimulation the ends of the fibrils reach 

 out, come in contact with other end fibrils of other cells, 

 and conduct their destined impulse. Again they re- 

 tract, and communication ceases for the time between 

 those particular cells. Meantime, by a different ar- 

 rangement of the various conductors, different sets of 

 cells are placed in communication, different associations 

 of nervous impulses induced, different trains of thought 

 engendered. Each fibril when retracted becomes a non- 

 conductor, but when extended and in contact with an- 

 other fibril, or with the body of another cell, it conducts 

 its message as readily as a continuous filament could do 

 precisely as in the case of an electric wire. 



431 





