58 FIXING AND HARDENING AGENTS 



siderable volumes of liquid should be taken, and the liquid should 

 be 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 jorogressively 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 transparent. Fat is not dissolved. 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. 



114. 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. iviss. Mikr., 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 (Encyl. mikr. Techn., i, p. 472) takes 5 of formol, 

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



Kahle's Fluid {Die Paedogenesis der Cecidomyiden, 1908, Stutt- 

 gart) : 



95 per cent, alcohol . . . .15 parts. 



Formol (commercial) . . . . 6 ,, 



Glacial acetic acid .... 1 part. 

 Distilled water . . . . .30 parts. 



This modification of Lavdowsky's fluid is much used these 

 days. 



115. Picro-Formol. P. Bouin {Phenomenes cyiologiques anor- 

 maux dans UHistogenese, etc., Nancy, 1897, p. 19) recommends — 



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

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

 most purposes one of the most valuable fixative yet made known. 

 It is rather a strong fixative, and should not be allowed to act for 

 more than eighteen hours. The penetration is great, the fixation 

 equable, delicate detail well preserved, staining qualities admir- 

 able, especially with iron-hematoxylin and Saiirefuchsin. 



