FIXING AND HARDENING AGENTS. 51 



structural elements. He finds also that the addition, of 

 acetic acid to bichromate not only suffices to ensure correct 

 fixation of nuclei (see 55), but also is favourable as regards 

 its action on cytoplasm. He recommends the following- 

 formula, it being understood that the proportions may be 

 varied if desired : 



Bichromate . . . . .3 grms. 



Glacial acetic acid . . . .5 c.c. 



Water 100 



Smaller objects to remain in the fluid for one or two days, 

 larger ones longer. Wash well in plenty of water, and pass 

 through alcohols of increasing strength, beginning with 15 

 per cent. The results may be compared with those of liquid 

 of Zenker, with the advantage that the ulterior treatment is 

 greatly simplified. 



The mixtures of bichromate with osmic acid have been given above, 

 48 and 49. 



57. MULLEE'S Solution. 



Bichromate of potash .... 2 2^- parts. 

 Sulphate of soda ..... 1 part. 



Water 100 parts. 



The duration of the reaction is about the same as with the simple solu- 

 tion of chromic salt. 



This fluid was very highly in vogue for many years, but seems lately to 

 be much less used. Recent authors find its action to be identical with that 

 of plain bichromate, and doubt whether the sulphate in it has any effect 

 whatever as regards its hardening properties. I fancy, however, that the 

 superiority of this mixture over the simple bichromate solution is not 

 illusory, and is due to the formation in it of a trace of free chromic acid. 

 Fol says that for mammalian embryos, for which it has been recommended, 

 it is worthless. 



58. ERLICKI'S Solution ( Warschauer med. Zeit., xxii, Nos. 15 

 and 18 (Progrh Urdical, 1897, No. 39).- 



Bichroniate of potash . . . 2'5 parts. 



Sulphate of copper . . . I'O part. 



Water lOO'O parts. 



Here the addition of the cupric sulphate is intelligible. 

 This salt is itself a hardening agent of some energy, and may 

 well serve to reinforce the somewhat slow action of the 

 bichromate. As a matter of fact, " Erlicki " hardens very 

 much more rapidly than either simple bichromate or Miiller's 



