506 CAJAL 



ever, it should be remembered that many investigators have 

 failed to obtain good results by the formaldehyde methods and 

 that they are unsuitable for embryonic specimens. 



HoYER, Jun. {Anat. Anz., ix, 1894, p. 236) was the first to 

 point out that material fixed in formalin could be used for carrying 

 out Golgi's method. 



Lachi (Monit. Zool. Ital., v, 1895, p. 15) used, at first, to 

 harden tissues for five to nine days in equal parts of 20 per cent, 

 formalin and 6 per cent, potassium bichromate. Afterwards 

 (Anat. Anz., x, 1895, p. 790) he adopted the mixture proposed 

 by his pupil Dell'Isola {Boll. Ace. Med. Genova, 1895, No. 2) 

 of equal parts of 10 per cent, formalin and 10 per cent, potassium 

 bichromate, with the addition of 1 part of 1 per cent, osmic acid 

 to every 10 of the mixture, this last formula being particularly 

 suitable for quick work, as forty-eight hours afterwards pieces 

 can be already transferred into the silver bath. 



Strong {Anat. Anz., x, 1895, p. 494) suggested fixing pieces 

 of brain of adult specimens in mixtures of 100 volumes of 3-5 

 per cent, potassium bichromate and from 2|- 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 | 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 {Proe. Amer. Micr. Soe., 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 0-75 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 1 of formalin ; after twenty- 

 four hours he transfers all pieces to pure 3-5 per cent, bichro- 

 mate 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, 1806, p. 108) first 

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



