Hardesty, spinal Nerves of the Frog. 34 1 



3. To a greater extent the distal excess may be due to 

 medullated fibers from the sympathetic system which terminate 

 within the spinal ganglion. 



4. It may be to a less extent due to the existence of cells 

 in the spinal ganglion which send processes toward the periph- 

 ery, but not toward the central system. 



These statements are based upon observations made both 

 in this laboratory and elsewhere. 



VII. The Changes in the Number of Fibers Found at Dif- 

 ferent Levels in the Dorsal and Ventral Roots 



AND IN THE NeRVE TrUNK. 



As has already been stated, counts were made of the fibers 

 present in sections taken at different levels of the two roots and 

 of the nerve trunk. Similar counts were made in the former 

 investigation, but there only two specimens were used, and 

 they differed but slightly in weight. The main object then was 

 to ascertain if possible, the manner and rate at which a 

 given specimen acquires in all its spinal nerves the addi- 

 tional fibers which it is known to acquire as it advances in 

 weight. In the present instance, quite a number of specimens 

 were employed differing widely in weight, and, in order to 

 shorten the task as much as possible, only one nerve was taken 

 from each specimen. 



For reasons given above, the 6th. spinal nerve was the one 

 nerve chosen. Sections were taken at the different levels of 

 the two roots and the trunk of this nerve as indicated in Fig. i. 



As already stated, an enumeration of the fibers contained 

 in the sections showed a variation in the numbers found 

 at the different levels of a root or of a trunk. This vari- 

 ation always consisted in the presence of a few more fibers in 

 that section nearest the cells giving origin to the fibers con- 

 tained in it. These variations found in the roots and trunk of 

 the 6th. nerve are similar to those found in the former paper 

 for the several spinal nerves of one frog. 



Bearing on this topic, there is but one other paper to be 

 considered. 



