464 AXIS-CYLINDER AND DENDRITE STAINS. 



brain of adult specimens in mixtures of 100 volumes of 3-5 per cent, 

 potassium bichromate and from 2-J to 5 volumes of formalin. One 

 or more pieces are, during several days, daily transferred into 1 per 

 cent, silver nitrate. Or the tissues are left for one to two days in 

 the above formalin-bichromate mixture and then passed into a fresh 

 one consisting of 2 volumes of 5 per cent, potassium bichromate 

 and 1 volume of formalin ; after another twelve to twenty-four 

 hours all the pieces are transferred into the silver bath. 



DURIG (ibid., p. 659) obtained good results by fixing J cm. thick 

 pieces in 3 per cent, bichromate containing 4 to 6 per cent, of formalin, 

 and hardening therein for three days. After silvering for two days, 

 the pieces are brought back into the fixing mixture and one proceeds 

 as in Ramon y Cajal's double impregnation process. 



FISH (Proc. Amer. Micr. Soc., xvii. 1895, p. 319) uses 2 c.c. of 

 formalin for every 100 c.c. of 3 per cent, potassium bichromate, and 

 leaves tissues three days in this fluid, and another three days in 

 -75 per cent, silver nitrate ; or, with advantage, Miiller's fluid, 

 100 c.c. ; 10 per cent, formalin, 2 c.c. ; 1 per cent, osmic acid, 1 c.c. ; 

 silvering as above. 



KOPSCH (Anat. Anz., xi, 1896, p. 727) uses 4 parts of 3-5 per cent, 

 potassium bichromate and one of formalin ; after twenty-four hours 

 he transfers all pieces to pure 3-5 per cent, bichromate for at least 

 two days (retina) or three to six (central organs). He finds that by 

 this means, precipitates are almost entirely avoided. B. Lee 

 (1913 ed.) confirms this, but points out that the method gives a too 

 abundant impregnation of capillaries. 



GEROTA (Intern. Monatsch. Anat., xiii, 1896, p. 108) first hardens 

 brains for a week or two in 5 to 10 per cent, formalin, then puts 

 small pieces for three to five days into 4 per cent, bichromate, 

 and lastly transfers these into the silver bath, where they are left 

 with advantage for ten to twenty days. 



BOLTON (Lancet, 1898 (1), p. 218 ; Journ. R. Micr. Soc., 1898, 

 p. 244) has obtained good results from brains of cats and half-grown 

 kittens placed whole in 5 per cent, formalin and from human brains 

 hardened whole in formalin of the same strength for two to twelve 

 months. Small pieces are then cut out, and placed into 1 per cent. 

 ammonium bichromate and left therein for from a few hours up to 

 five days, some being transferred at intervals into 1 per cent, silver 

 nitrate. 



SCHREIBER (Anat. Anz., xiv, 1898, p. 275) obtained good results 

 from appendages of Crustacea impervious to the osmic mixture, with 

 5 parts of 2-5 per cent, potassium bichromate to 1 of 4 per cent. 



