378 CHAPTEK XXXI. 



augments in weight slightly in 10 per cent, formol solution 

 (spinal cord somewhat more) ; whilst in 1 per cent, solution 

 it may increase as much as 24 per cent. 



GEKOTA (Zeit. iciss. Mik., xiii, 1896, p. 314) puts human 

 brains into a 5 or 10 per cent, solution of formol, and after 

 twenty-four hours removes the pia and changes the liquid ; 

 this is also further done every five to seven days, and in one 

 or two weeks the hardening is complete. In the case of 

 foetal brains of Gam's, Felts, and Homo, he first injects the 

 vascular system with a 10 to 15 per cent, solution of formol 

 in 85 per cent, alcohol, and then brings the heads into the 

 5 to 10 per cent, watery solution ; after one or two days he 

 removes the brains from the skull and puts them back for 

 fifteen to twenty days into the formol. 



KADYI (Poln. Arch. Biol. Ned. Wiss., i, 1901, p. 80) takes 

 5 parts of formol, 100 of water, and 2 of bicarbonate of soda, 

 for four to ten days. 



HRDLICKA (Prnc. U. 8. Nut. Mus., xxx, 1906, p. 304) takes 

 3 parts of formol, 25 to 45 of water, and 72 to 52 of alcohol 

 of 1)5 per cent. 



STRECKER (Zeit. wiss. Mik., xxviii, 1911, p. 17) fixes small pieces for 

 twenty-four to forty-eight hours in 1 part of formol of 10 or 20 per cent, 

 with 1 part of Ehrlich-Biondi triacid mixture, and imbeds in paraffin, 

 thus getting a stain at the same time as a fixation. Similarly with 

 toluidin blue, fixing it with ammonium molybdate. 



742. Chromic Salts.' That most used is the bichromate of 

 potash. 



The liquid of ERLICKI has a more rapid action than the 

 other solutions of chromic salts. SAHLI, however (loc. cit., 

 739), after having studied the action of the usual solutions, 

 concludes that the best hardening 1 a^ent for fresh tissues is 



O t) 



pure bichromate of potash, in 3 or 4 per cent, solution, the 

 hardening being done in a cold place. He rejects the liquid 

 of Erlicki on account of the precipitates it so frequently 

 gives rise to (see 54). 



OBERSTEINEK is of the same opinion, recommending pure 

 bichromate for general hardening purposes; whilst for the 

 study of the most delicate structural relations he recommends 

 fixing in Fol's modification of Flemming's liquid ( 42) for 

 twenty-four hours, followed by washing with water and 

 hardening in SO per cent, alcohol. 



