466 AXIS-CYLINDER AND DENDRITE STAINS. 



of 2 per cent, potassium bichromate to which after ten to fifteen minutes 

 5 c.c. of 1 per cent, osmic acid are added. The mixture is kept in the 

 dark and after twenty -four hours changed for a fresh one made up 

 with 90 c.c. of 2 per cent, bichromate and 10 c.c. of 1 per cent, osmic 

 acid. After another two days the mixture is changed over again for 

 one made according to the proportions given by Golgi (3 per cent, 

 potassium bichromate, 80 c.c. ; 1 per cent, osmic acid, 20 c.c.). Pieces are 

 transferred into the silver bath after three and a half days (for nerve 

 cells and neuroglia) up to six days. They are washed for five to fifteen 

 minutes in f per cent, silver nitrate, and then put into a solution of 

 silver nitrate of the same strength, but to which 1 drop of formic acid 

 to every 100 or 120 c.c. of solution has been added. The whole is kept 

 in an incubator at 25 to 27 C. for about three days, changing the 

 silver bath after the first twenty -four hours. The same author advised, 

 for the impregnation of neuroglia (Intern. Monatschr. Anat. x, 1893, 

 p. 533), adding 1 drop of a saturated solution of chromic acid and 1 drop 

 of formic acid to the first hardening bath. 



BERKELEY (Johns Hopkins Hosp. Bep., vi, 1897, p. 1) hardens tissues 

 in Miiller's fluid until they are of sufficient consistency to admit of fairly 

 thin sections (about two weeks at room temperature). The portions 

 of the brain selected are cut into slices 3 mm. thick and immersed for 

 about three days in a mixture of 3 per cent, potassium bichromate, 100 

 parts, and 1 per cent, osmic acid 30 parts. For the impregnation, 

 tissues are removed from the hardening fluid, dried a little with filter 

 paper, washed in a weak solution of silver nitrate, and put for no less 

 than two to three days into a freshly prepared solution of 2 drops of 

 10 per cent, phosphomolybdic acid and 60 c.c. of 1 per cent, silver 

 nitrate, which in winter should be kept at a temperature of about 26 C. 



HILL (op. cit. 884) uses, instead of silver nitrate, a f per cent, solu- 

 tion of silver nitrite, with 0-1 per cent, formic acid added. 



GUDDEN (Neurol CentrU., xx, 1901, p. 151) uses the lactate of silver 

 (sold as " actol "), and finds it more penetrating. 



891. Avoidance of Precipitates. Golgi's method frequently gives 

 rise to the formation at the surface of the pieces of irregular and 

 sometimes voluminous precipitates, which destroy the clearness of 

 preparations. To minimise this, SEHRWALD (Ztschr. wiss. Mikr., 

 vi, 1889, p. 456) pours 10 per cent, gelatin, which is just liquid, into 

 a paper box, embeds the tissues in it with the aid of a little heat, 

 and brings them therein into the silver bath ; or the tissues are 

 coated with gelatin by dipping and cooling several times. After 

 the impregnation is completed the gelatin is removed, before cutting, 

 by means of warm water saturated with silver chroma te. MANN 

 (Physiol. Histol, 1902, p. 276) finds that the method gives good 

 results provided the gelatin is not rendered insoluble by the action 

 of light. To prevent this he proceeds thus : Either in the photo- 

 graphic dark room or in the evening, by artificial light, tissues, 

 tied loosely to a thread, are immersed three times into liquefied 



