52 FIXING AND HARDENING AGENTS. 



acid serves to counteract in a marked degree the softening action of the 

 acetic acid. 



Acetic acid, used alone, is only a fixative for a limited time. If its 

 action be prolonged, it becomes a swelling agent. Its function in 

 mixtures is, besides that of killing, the valuable one of counteracting the 

 shrinking action of the ingredients with which it is combined, and by its 

 swelling action enhancing the penetration of the mixture ; whilst by 

 clarifying tissues it adds to the optical differentiation of their elements. 



The proportions in which it should enter into mixtures in general seem 

 to me to be from 0-5 per cent, to 5 per cent, of the glacial acid ; higher 

 strengths, such as 25 per cent, to 100 per cent., being only indicated in 

 cases in which the highest possible penetration is the chief consideration. 



Throughout this work, wherever acetic acid is mentioned, it is the 

 glacial acid that is meant unless the contrary is stated. 



All liquids containing a large proportion of this acid (e.g., 85, 

 86) should only be allowed to act for a very short time. 



85. Acetic Alcohol (CARNOY, La Cellule, iii, 1886, p. 6 ; and ibid., 

 1887, p. 276; v. BENEDEN et NEYT, Bull. Ac. Sri. Belg., xiv, 1887, 

 p. 218 ; ZACHARIAS, Anat. Anz., iii, 1888, pp. 24 27 ; v. GEHUCH- 

 TEN, ibid., 8, p. 227). CARNOY has given two formulae for this 

 important reagent. The first is- 



Glacial acetic acid .... 1 part. 

 Absolute alcohol . . . .3 parts. 

 The second is- 



Glacial acetic acid . . .1 part. 



Absolute alcohol . . , . 6 parts. 

 Chloroform . . . . 3 ,, 



The addition of chloroform is said to render the action of the 

 mixture more rapid. 



V. BENEDEN and NEYT take equal volumes of glacial acid and 

 absolute alcohol. 

 ZACHARIAS takes- 

 Glacial acetic acid . . .1 part. 

 Absolute alcohol . . . .4 parts. 

 Osmic acid . . . . .a few drops. 

 Acetic alcohol is one of the most penetrating and quickly acting 

 fixatives known. It preserves both nuclei and cytoplasm, and 

 admits of staining in any way that may be preferred. It was 

 employed by all of the authors quoted for the ova of Ascaris- 

 proverbially one of the most difficult objects to fix, but I have 

 found that it is applicable to many other objects. Wash out with 

 alcohol, and avoid aqueous liquids as far as possible in the after- 

 treatment. 



