370 NERVES. 



Medullated fibres dark blue on a light, sometimes rosy 

 ground. If it be wished to have the ground particularly 

 colourless, take instead of the second wash-water a mixture 

 of -J- to J volume of common (not glacial) acetic acid with 100 

 volumes of water. Thick sections or series in celloidin require 

 a special differentiation. They may be differentiated either 

 with the above-mentioned acetic acid mixture, or in the usual 

 borax-ferricyanide mixture diluted with water. In the latter 

 case the ground will be yellow. 



If the impregnation with the copper be imperfect (as, for 

 instance, may happen if the treatment with the copper salt 

 be performed at the normal temperature instead of in an in- 

 cubator) some instructive differentiations of ganglion-cells 

 may be obtained, the processes of the cells of Purkinje in 

 the cerebellum, for instance, being very sharply brought out ; 

 but such preparations have a tendency to after-blackening, 

 which does not happen with those that have been thoroughly 

 impregnated with the copper. 



The advantages of the improved method are that differen- 

 tiation after staining is not necessary ; that the annoying pre- 

 cipitates formed on the surface of the preparations by the 

 copper in the old method do not appear ; that the divers 

 manipulations are simpler and easier; the preparations are 

 equal in beauty to those of Pal, and can be obtained with 

 greater certainty. 



704. GOLGI'S Nerve Methods Bichromate and Silver Nitrate 

 Process, or "Slow" Method. I take the following resume of 

 this method from the interesting paper of Grolgi's pupil, REZ- 

 ZONICO, "Sulla struttura delle fibre nervose del midollo 

 spinale," in the Archivio per le scienze mediche, iv, No. 4 

 (1879), p. 85. 



1. Take pieces of perfectly fresh spinal cord, and soak 

 them in a 2 per cent, solution of bichromate of potash for a 

 period of time varying according to temperature. (In summer 

 eight to fifteen days may suffice, in winter about a month is 

 necessary.) 



2. Wash them, and put them into a 0*75 per cent, solution 

 of nitrate of silver. The period of immersion therein depends 

 on the temperature : in summer the reaction will be complete 

 throughout the tissues in two or three days ; in winter, eight, 

 ten, or more days. 



