CHEOMO-NITE1C ACID. 27 



39. Chromo -nitric Acid (PERENYI'S formula) (Zool. Anzeig., 

 v (1882), p. 459). 



4 parts 10 per cent, nitric acid. 



3 parts alcohol. 



3 parts 0'5 per cent, chromic acid. 



These are mixed, and after a short time give a fine violet- 

 coloured solution. 



The objects (ova) are immersed for four to five hours, and 

 then passed through 70 per cent, alcohol (twenty-four hours) 

 strong alcohol (some days), absolute alcohol (four to five 

 days) . They are then fit for cutting. The advantage of the 

 process is stated to be that segmentation spheres and nuclei 

 are perfectly fixed, the ova do not become porous, and cut 

 like cartilage. 



Another advantage is that the fixing solution may be com- 

 bined with a stain. (In this case the albuminous envelopes 

 of the ova must be carefully removed, otherwise the stain will 

 not penetrate.) 



Some stains, such as fuchsin or anilin red, may be dis- 

 solved directly in the fixing solution. Others, such as eosin, 

 purpurin, anilin violet, must first be " dissolved in three parts 

 of alcohol, and then shaken into the liquid." 



Picro-carmine and borax-carmine may be added to the 

 liquid, but they give rise to a precipitate, which must be re- 

 moved by filtration before using. 



Chromo-nitric acid is above all an embryological reagent, 

 and a very important one. 



Another formula given by Perenyi (Zool. Anzeig.,274>, 1888, 

 p. 139, and 276, p. 196) is as follows : 



3 parts 20 per cent, nitric acid. 



3 parts 1 per cent, chromic acid. 



4 parts absolute alcohol. 



For embryos of Lacerta. Fix for twenty minutes. Wash 

 out for an hour with 70 per cent, alcohol, and then with 

 strong alcohol. Stain with Delafield's ha3matoxylin, and treat 

 the stained material for three to five minutes with 1 per cent, 

 chromic acid. 



40. Chromo-nitric Acid with Bichromate (KOLLMANN, Arch. f. 

 Anat. u. Phys., 1885, p. 296). 



Bichromate of potash 5 per 100 



Chromic acid . . . . . . 2 ,, 



Concentrated nitric acid 2 



