NON-MEDULLATED NERVE FIBERS 69 



Both of these silver methods are very unreUable in so far as 

 their application to the spinal nerves is concerned. By treating 

 the tissue with pyridine before it is put into silver nitrate the stain- 

 ing of the non-medullated fibers is rendered much more intense. 

 The reaction appears to be very constant and few failures need 

 be anticipated if pure chemicals are used. The method is appli- 

 cable to much smaller nerves than can be successfully treated 

 with Cajal's method, and gives a more uniform impregnation 

 throughout the nerve. The technique is as follows: The nerve 

 or ganghon is placed in 100 per cent alcohol with 1 per cent am- 

 monia for forty eight hours. (95 per cent alcohol with 5 per 

 cent ammonia will give much the same results but seems more 

 likely to bring out the nurilemma nuclei.) The pieces are then 

 washed for from one-half to three minutes (according to their 

 size) in distilled water and transferred to pyridine for twenty- 

 four hours, after which they are washed in many changes of 

 distilled water for twenty-four hours. They are then placed in 

 the dark for three days in a 2 per cent aqueous solution of silver 

 nitrate at 35° C, then rinsed in distilled water and placed for one 

 to two days in a 4 per cent solution of pyrogalic acid in 5 per 

 cent formalin. Sections are made in paraffine and after mount- 

 ing are ready for examination. 



All of the illustrations shown in this paper were made from 

 Cajal preparations before the pyridine-silver method was de- 

 veloped. The preparations obtained by the latter however do 

 not differ in any essential point from those by Cajal's method 

 which have served as the basis for the illustrations and descrip- 

 tions in this paper. 



HISTOLOGICAL OBSERVATIONS 



When a satisfactory Cajal preparation is cut into transverse 

 sections one finds the axons of the medullated fibers stained a 

 hght brown (figs. 1 and 7). These are surrounded by a colorless 

 ring, representing the myeUn sheath; or there may be a very 

 light yellow stain in the neurokaratin framework. The neuri- 

 lemma fs not clearly differentiated and the axon often appears 



