1 1 4 Journal of Comparative Neurology and Psychology. 



vous system. The objection maybe raised that the period which 

 elapsed was not long enough, that the degeneration was simply 

 incomplete, that the distal endings of the fibers form the net- 

 works and that these were still in their normal condition. But 

 we have already seen that the distal endings of most of the 

 medullated nerves, the terminal fibrillae in the sensory organs, 

 have completely degenerated. Why do the fibers of the net- 

 works alone fail to show similar changes? 



It has been shown in the first part of this paper that the 

 fibers of these networks are nerve fibers. It cannot be main- 

 tained therefore that they do not degenerate because they are 

 non-nervous structures. The only explanation of their immunity 

 from the degenerative changes which affect the isolated medul- 

 lated nerves is that the cells of the network exert upon them a 

 distinct trophic influence. The cells are then something more 

 than sheath cells or connective tissue cells as Bardeen and 

 others have asserted. The medullated fibers of the palate are 

 well supplied with sheath cells but this does not prevent their 

 degeneration when separated from their ganglion cells. We 

 can only conclude that the cells of these networks are true 

 nerve cells in that the integrity of the fibers is dependent upon 

 them. This is in strict agreement with the conditions which 

 we find in the nervous system of the lower animals, and sub- 

 stantiates the conclusions of Bethe and Leontowitsch 



As to whether these networks of nerve cells and fibers 

 will retain their integrity indefinitely when severed from all con- 

 nection with the central nervous system, we do not know at 

 present. Experiments are in progress to determine whether 

 they also will degenerate in the course of a few months, or 

 whether they possess the power of regenerating new fibers. 

 Bethe (:03) maintains that the sheath nuclei are modified nerve 

 cells and still retain their primitive function of neurogenesis. It 

 might be expected that these peripheral nerve cells possess a 

 similar function. Our present data are not sufficient however 

 to warrant the assumption of Leontowitsch that there is a con- 

 stant process of physiological regeneration going on in the 

 skin, and that the subepithelial network is transformed into the 



