62 FIXING AND HARDENING AGENTS. 



renewed from time to time ; for the formaldehyde fixes itself on the 

 tissues with which it comes in contact, deserting the solution, which 

 thus becomes progressively weaker. The specimens should be 

 suspended in the liquid or otherwise isolated from contact with the 

 containing vessel. The hardening obtained is gentle and tough, 

 giving an elastic and not a brittle consistency. It varies greatly 

 with different tissues. Mucin is not precipitated and remains trans- 

 parent. Fat is not dissolved (see 768 et seq.). Micro-organisms 

 retain their specific staining reactions. Formaldehyde is said to 

 harden celloidin as well as gelatin, and to be useful for celloidin- 

 imbedding (BLUM, Anat. Anz., xi, 1896, p. 724). 



Several of the following mixtures are irrational, becoming reduced 

 more or less quickly, but may give good results all the same. 



109. Alcoholic Formol (LAVDOWSKY, Anat. Hefte, iv, 1894, p. 361). 

 Water 40 parts, 95 per cent, alcohol 20, formol 6, acetic acid 1 ; or water 

 30, alcohol 15, formol 5, acetic acid 1. 



GULLAND (Zeit. wiss. -Milcr., xvii, 1900, p. 222) takes (for blood) 

 1 part formol and 9 parts of alcohol. 



BLES (Trans. Roy. Soc. Edinburgh, xli, 1905, p. 792) takes 7 of formol, 

 90 of alcohol of 70 per cent., and 3 of acetic acid. 



TELLYESNICZKY (Encycl. mikr. Techn., i, p. 472) takes 5 of forrnol, 

 100 of alcohol of 70 per cent., and 5 of acetic acid. 



110. Picro-Formol. P. BOUIN (Phenomenes cytologiques anormaux 

 dans L' Histogenese, etc., Nancy, 1897, p. 19) recommends 



Picric acid, saturated aqueous sol. . . 75 parts. 



Formol 25 



Acetic acid . . . . . 5 



Wash out with alcohol, first of 50 per cent., then 70 per cent, till 

 the picric acid is mostly removed. I consider this to be for most 

 purposes the most valuable fixative yet made known. I have 

 satisfied myself that the proportions are exactly what they should 

 be and cannot be changed without hurt. It is rather a strong 

 fixative, and should not be allowed to act for more than 18 hours. 

 If a weaker mixture be desired, dilute the whole with water. The 

 penetration is great, the fixation equable, delicate detail well pre- 

 served, staining qualities admirable, especially with iron-hematoxylin 

 and Saiirefuchsin. See also " Cytology " sections, 656, under 

 heading of " Chromosomes and Urea," and GARNIER, Bibl. Anat., 

 v, 1898, p. 279. 



The formulae of GRAF (State Hosp. Bull. New York, 1897 ; Journ. Roy. 

 Mie. 8oc., 1898, p. 492) are in my view too weak. 



MOKEAUX (BiU. Anat., 1910, p. 265) takes 15 parts formol, 85 of 

 trichlor- acetic acid of 3 per cent., and picric acid to saturation. 



