NON-MEDULLATED NERVE FIBERS 73 



separated, than in other parts of this section, or in other sections 

 of the human sciatic, it follows that the photograph represents 

 approximately the maximum number of myelin sheaths for an 

 area of that size in the human sciatic nerve. In fig. 7 there 

 are many more axons than could be ringed by that number of 

 myelin sheaths. The same numerical relations are brought out 

 in figs. 4 and 5, which are camera lucida tracings from the sciatic 

 nerve of the dog. Fig. 4 is from a Stroebe preparation and repre- 

 sents the myelin sheaths as solid black rings. Fig. 5 is from a 

 Cajal preparation and represents medullated axons in stipple 

 and non-medullated axons in solid black. It is clear that there 

 are many more axons than there are myelin sheaths. 



These non-medullated fibers have been demonstrated in the 

 cervical and lumbar nerves of animals (dogs, cats, and rabbits) 

 close to the ganglia, as well as in the longitudinal fiber bundles 

 within the ganglia, both on the peripheral side when they are 

 about to join the ventral roots and on the central side just before 

 the dorsal root fibers leave the ganglion. These fibers correspond 

 in every way with those seen in the sciatic nerves. From this 

 evidence alone it would seem probable that at least a considera- 

 ble proportion of, these fibers seen in the peripheral nerves either 

 arise in, or pass through the spinal ganglion. Satisfactory prep- 

 arations of the ventral roots and of the dorsal roots beyond the 

 ganglia have not been obtained. This is probably due to the 

 small size of the radicles of which the roots are composed. This 

 difficulty in technique has greatly retarded the work of tracing 

 these fibers toward the central nervous system.^ 



' Since this paper was written Mr. Chase, working in this laboratory with the 

 pyridin-silver method, has obtained a very beautiful demonstration of the non- 

 medullated fibers in the dorsal root of a spinal nerve of the dog. He has kindly 

 permitted me to mention this observation in advance of the completion of his 

 investigation of the roots of the spinal nerves. 



