OS S. WALTER RANSON 



any of the medullated nerve fibers. Osmic acid could not be 

 used as a stain for the myelin sheaths because it will not pene- 

 trate to the center of a nerve large enough to give a satisfactory 

 preparation by any of the silver methods. 



For the demonstration of the axons those methods which 

 cause a deposit of reduced silver in the axons give by far the best 

 results. Of these procedures three were successfully applied, 

 Carjal's method, Bielschowsky's method, and a new method, 

 developed during the course of this investigation, which involves 

 the use of pyridine. All three are closely related and give 

 similar pictures. Cajal's method, which is the original and of 

 which the others are only modifications, is carried out as follows. 

 Pieces of fresh nerve (preferably a large nerve like the human 

 sciatic) are placed for two days in absolute alcohol containing 

 1 per cent of concentrated ammonia; washed one to throe minutes 

 in distilled water; placed for three to five days in a 1^ per cent 

 aqueous solution of silver nitrate in the dark at 37° C; washed 

 three to five minutes in distilled water; placed for one to two 

 days in a 1 per cent solution of hydroquinone in 10 per cent 

 formalin. The tissue is then imbedded in paraffin and cut into 

 sections, which, after mounting, are ready for examination. The 

 preparations may sometimes be improved by treating the sections 

 on the slide with a neutral gold bath containing five drops of a 

 1 per cent gold chloride solution to each 10 cc. of water. This 

 method is uncertain in its results and only occasionally gives 

 satisfactory preparations of the spinal nerves. At best it is 

 only a limited part of the section which is fit for examination. 

 But, when a satisfactory preparation is obtained, the work is 

 well repaid by the clearness with which all the axons are demon- 

 strated. 



Bielschowsky's method, for some unknown reason, could not 

 be successfully applied to animal nerves. Very beautiful prepa- 

 rations were obtained by its use on the human sciatic, and these 

 confirmed in every way the findings by Cajal's method. Since 

 it does not seem to be generally applicable the details of the pro- 

 cedure will not be given. They can be obtained from Biel- 

 schowsky's own account of his method ('05). 



