422 Journal of Applied Microscopy. 



Ganglion cells produce that which shall be conducted ; nerve cells, that which 

 shall conduct. 



At some stage in its development, a cell may begin to form a definite pro- 

 duct, and through this differentiate itself so that it may no longer be demonstra- 

 ble as a morphological unit, while it still forms a specific product which functions 

 for it, and may have a nucleus and a more or less clearly difterentiated cell body. 

 With this explanation, he describes the nerve cell as having a nucleus lying 

 within the lumen of the nerve fiber among the primitive fibrils, and separated 

 from them by a spindle-shaped space. Near the nucleus the cell divides prox- 

 imad and distad into branches which form nerve fibers. True anastomoses 

 occur between the nerve cells by means of these branches. 



In their origin nerve fibers may be considered more in the nature of proto- 

 plasmic cell-bridges which exist from the first division of the egg cell to the cells 

 of the developed organism. All these are primarily merely intercellular bridges 

 of undift'erentiated protoplasm, whether they originate in this way or as processes 

 of certain cells. Such a bridge may possess a certain power of conductivity, 

 but it first becomes a nerve when the specific conducting substance, the neuro- 

 fibril, is differentiated in it, just as a muscle cell, although it may be capable of 

 contractility, becomes a muscle only when the specific contractile substance, the 

 myofibril, forms, and is disposed in a certain way. No plexus is formed in the 

 ciliated cells. Instead, a fibril enters at the base of the cell and divides into a 

 brush, or pencil, one fibril of which goes to each cilium. The nerve fibril is 

 distinguished from the cilium by its dififerent reaction to stains, and by its 

 appearance in polarized light. 



In the muscles, one fibril penetrates each muscle cell, where it forks, without 

 forming a plexus, or becoming intimately associated with the nucleus, and passes 

 out of the cell. He finds a closed plexus extending through the epithelium of 

 the nephridia, in the intestinal wall, and in the walls of the capillaries. There 

 is a continuous going over of primitive fibrils from one conducting tract to 

 another, both in the centrum and in the periphery, and there are anastomoses 

 between the ganglion cells. 



Knowledge of the extent of these nerve fibrils is limited by the power of the 

 microscope. Apathy is not able to find any definite ending for the finest sensory 

 fibrils, and suggests that they may form a closed elementary plexus in the sub- 

 cuticula, comparable with the capillaries of the circulatory system. " Eine eiidi- 

 gung des Leitenden ist Jiirgends zu constatircii.''' E. m. b. 



Bernstein, J. Zur Konstitution unci Reizleit- (1) The irritable living substance of 

 ling der lebenden Substanz. Biol. Ctibl. nerve and muscle fibers is composed of 

 • - ; - 5' ))■ molecules imbedded in nutrient fluid 



— paraplasm, neuroplasm, sarcoplasm, cell sap. Molecules are aggregated in 

 longitudinal rows in fibers or fibrillai, and held together by chemical affinity 

 which is equivalent to chemical valence. 



(2) The rows of molecules may be polarized longitudinally, but not trans- 

 versely, by the electric current. 



(3) It is assumed that there are certain atomic groups adhering to the 



