NON-MEDULLATED NERVE FIBERS 71 



investigation. At the present time we are concerned only with 

 showing that the axons under discussion are identical with those 

 designated as non-medullated, and are entirely distinct from, and 

 in addition to, the medullated axons, which alone have hereto- 

 fore been taken into consideration in the spinal nerves. 



Teased preparations of nerves prepared according to Cajal's 

 method are readily made. After the impregnation and reduction 

 are complete the nerves are dehydrated, cleared and teased in 

 creosote. In such preparations one can see the axon of the 

 medullated fibers surrounded by a faintly stained network of 

 neurokeratin representing the myelin sheath; even on the finest 

 of such fibers the nodes of Ranvier can be found. Among these 

 can be seen the non-medullated fibers running in bundles or 

 alone. Often an axon can be seen running from one bundle to 

 another. Closely applied to them in favorable preparations can 

 be seen elongated nuclei with their long axes corresponding to 

 that of the fiber and resembling neurilemma nuclei on the sym- 

 pathetic fibers (fig. 3). One non-medullated fiber was followed 

 for a considerable distance and showed four such nuclei; but no 

 trace of a node of Ranvier could be found. 



In order to compare the fibers under discussion with the sym- 

 pathetic non-medullated fibers preparations were made by Cajal's 

 method from the semilunar sympathetic ganglion of a dog. 

 Scattered medullated fibers could be seen in these preparations 

 but the great majority of the fibers were non-medullated and 

 differed only in their grouping from those of the spinal nerves 

 herein described. The non-medullated fibers in the sympathetic 

 ganglion are uniformly and solidly massed together into large 

 fascicles, while in the spinal nerves they are grouped into small 

 bundles widely separated by intervening medullated fibers. 



All the methods based upon the reduction of silver in the axon 

 (Cajal's, Bielschowsky's and the new pyridine-silver method 

 presented in this paper) often stain connective tissue fibers. 

 Both the elastic and white fibers have been stained in some of the 

 preparations of the spinal nerves. The white fibers are much 

 too delicate to be mistaken for axons; and the elastic fibers are 

 readily recognized by their isolated course and characteristic 



