

BICHROMATE OF AMMONIA. 47 



78. Miiller's Solution, 



Bichromate of potash . . 2 2J parts. 



Sulphate of soda ... 1 



Water 100 



The duration of the reaction is about the same as with the 

 simple solution of chromic salts. 



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

 seems lately to be much less used. I confess that I do not 

 understand what is the part played by the sodic sulphate, and 

 that I fancy that the superiority of this mixture over the 

 simple bichromate solution is mostly illusory. Fol says that 

 for mammalian embryos, for which it has been recommended, 

 it is worthless. 



79. Erlicki's Solution (Warschauer med. Zeit., xxii, Nos. 15 

 and 18). 



Bichromate of potash . . 2*5 parts. 

 Sulphate of copper . . 1*0 



Water lOO'O 



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 solution. A 

 spinal cord may be hardened in it in four days at the tem- 

 perature of an incubator, and in ten days at the normal 

 temperature (FoL, Lehrb. d. vergl. mik. Anat., p. 106). I 

 believe it to be one of the best hardening agents known for 

 voluminous objects. Human embryos of several months may 

 be conveniently hardened in it. 



Nerve-centres that have been hardened in Erlicki's fluid frequently con- 

 tain dark spots with irregular prolongations, simulating ganglion-cells. 

 These were at one time taken to be pathological formations, but they are now 

 known to consist of precipitates formed by the action of the hardening fluid. 

 They may be removed by washing with hot water, or with water slightly 

 acidified with hydrochloric acid, or by treating the specimens with 0*5 per 

 cent, chromic acid before putting them into alcohol (TscniscH, Virchow's 

 Arch., Bd. xcvii, p. 173 ; EDINGEE, Zeit.f. wiss. Mik., ii, 2, p. 245 ; LOEWEN- 

 THAL, Rev. Mod. de la Suisse romande, 6me annee i, p. 20). 



80. Bichromate of Ammonia. A review of the literature of the sub- 

 ject shows that this salt is in considerable favour, for what precise motive is 

 not apparent. Its action is very similar to that of the potassium salt. Fol 



