MINERAL ACIDS AND THEIR SALTS 33 



work. Lee found it altogether excellent for preserving marine 

 organisms, especially large forms. Strong alcohol need only be 

 vised if the objects are destined to be sectioned. 



Another advantage is that the fixing solution may be combined 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 dissolved 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 

 liq-uid." 



Picro-carmine and borax-carmine may be added to the liquid, but 

 they give rise to a precipitate, which must be removed by filtration 

 before using. 



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 hsematoxylin and treat the stained material for three to five 

 minutes in 1 per cent, chromic acid. 



46. Chromo-formic Acid (Rabl, Morph. Jahrb., x, 1884, pp. 215, 216). 

 Four or 5 drops of concentrated formic acid are added to 200 e.c. of 

 0-33 per cent, chromic acid solution. The mixture must be freshly 

 prepared at the instant of using. Fix for twelve to twenty-four hours, 

 wash out with water. Used by Rabl for the study of karyokinesis. 

 (See also under Formic Acid, § 123.) 



47. Chromo-aceto-osmic Acid (Flemmixg, Zellsubstanz, Kern 

 und ZeUtheilung, 1882, p. 381). First or Weak formula : 



Chromic acid . . .0-25 per cent. ] 



Osmic acid ... 0-1 " | "^ water. 



Glacial acetic acid . . 0-1 ,, ) 



Meves [Encycl. mikr. Techn., 1, p. 475) sometimes added 1 per 

 cent, of sodium chloride. See also § 31. 



FoL {Lehrb. d. vergl. mik. Anat., 1884, p. 100) recommends the 

 following variant : 



1 per cent, chromic acid ... 25 vols. 



1 per cent, osmic acid ... 2 ,, 



2 per cent, acetic acid ... 5 ,, 

 Water ...... 68 „ 



— that is to say, a mixture weaker in osmium than Flemming's. 



A mixture still weaker than this in osmimii, viz. with 1 vol. osmic 

 acid solution, instead of 2, has been recommended by Cori {Zeit. iviss. 

 Mik., vi, 1890, p. 441). 



Second or Strong formula {Zeit. iviss. Mik., 1, 1884, p. 349) : 



1 per cent, chromic acid . . .15 parts. 



2 per cent, osmic acid . . . . 4 ,, 

 Glacial acetic acid .... 1 part. 



VADE-MECUM. 2 



