126 'JoiirnaJ of Comparative Neurology and Psychology. 



spinal ganglion slion'd be divided into two types represented by the 

 large and the small cells which diU'er both anatomically and physi- 

 ologically from each other. The large cells, which in the second 

 cervical ganglion of the white rat constitute a third of the total 

 number, are connected with medullated fibers. The remaining two- 

 thirds are small cells and these are associated with non-medullated 

 fibers which divide injto central and peripheral fibers after the 

 manner of a T or Y. These non-medullated fibers can be traced 

 into the dorsal root and toward the periphery as far as the junction 

 point of the afterent and efferent fibers.* 



It is believed that these fadts, together with the observations 

 in the present paper, make it possible to explain the conflicting 

 resuHs presented in the paper on ''Retrograde Degeneration." At 

 the time that paper w^as written there were certain technical diffi- 

 culties in the way of deciding whether any particular type of cell 

 was chiefly affected by the destructive process. This question had 



*After this paper had gone to the press the importaut book of Dogiel, "Der 

 Bau der Spinalganglien," came to hand. He finds eleven tj'pes of spinal 

 ganglion cells according to the character of their processes, with the greatest 

 conceivable wealth of collaterals and dendrites. Nevertheless in seven out 

 of the eleven types the fundamental character of the spinal ganglion cell is 

 maintained in that the axons divide after the manner of a T or Y into central 

 and peripheral fibers. Our belief that the vast majority of the fibers arising 

 in the spinal ganglion divide after this manner is thus confirmed, although 

 a hurried examination of the book might lead to the opposite conclusion. 



In the four remaining types (III, IV, VIII and XI) he was unable to de- 

 monstrate this division and the destination of these axons remains hypo- 

 thetical. For the piu-poses of the present paper these types take the place 

 of his old Type II which he has abandoned. He thinks it probable that these 

 cells are not connected with fibers in the peripheral nerve. In this paper we 

 have attempted to show that there are cells in the ganglion which because of 

 their failure to react to lesions of the peripheral nerve can have no axon 

 in the nerve. These non-reacting cells would correspond as well to his new 

 Types III, IV, VIII and XI as to his old Type II. 



He still maintains that the small cells give rise to non-medullated fibers 

 and the large ones to medullated fibers. On page 33 he states that the axon 

 "after its exit from the capsule becomes covered with a sheath of myelin 

 or in the case of the small cells and fine fibers it remains non-medullated 

 even to its bifurcation." In Type III, which consists of large cells, all the 

 axons are medullated, and in Type X, which consists of small cells, all the 

 axons are non-medullated. 



