FIXING AND HARDENING AGENTS. 73 



brought about by the coagulating action of pure alcohol, and the precipita- 

 tion on the surface of organs of the salts contained in sea-water, which is a 

 hindrance not only to the penetration of the alcohol, but also to subsequent 

 staining. 



Acid alcohol as above prepared loses its original qualities after standing 

 some time, as chloride of ethyl is gradually formed at the expense of the 

 acid. Seventy per cent, alcohol may be taken instead of 90 per cent, for 

 making the mixture, but is not quite so good. 



Lo BIANCO (Mitth. Zool. Stat. Neapel, ix, 1890, p. 443) takes 50 percent, 

 alcohol with 5 per cent, of hydrochloric acid. 



103. Pyridin. Pyridin has been recommended as a hardening agent 

 (by A. DE SOUZA). It is said to harden, dehydrate, and clear tissues at the 

 same time. They may be stained after hardening by anilin dyes dissolved 

 in the pyridin, or passed through water and stained by the usual processes. 

 It is said to harden quickly, and to give particularly good results with brain. 

 See Comptes Rendus hebd. de la Soc. lie Biologic, 8 ser., t. iv, No. 35, 

 p. 622 ; Zeit.f. wise. Mik., v, i, 1888, p. 65 ; Journ. ttoy. Mic. Soc., 1888, 

 p. 1054. 



104, Formaldehyde (Formol, Formalin, Formalose;. Formal- 

 dehyde is the chemical name of the gaseous compound HCOH, 

 obtained by the oxidation of methyl-alcohol. " Formalin " is 

 the commercial name given by SCH KRING & Co. to a 40 per cent, 

 solution of this substance in water. " Formol " is the com- 

 mercial name given to the same solution by MKISTKU, Lucius 

 & BKUNING. And " Formalose " is the name for ihe same 

 solution adopted by an American firm. (These solutions may 

 now be obtained from dealers in photographic chemicals.) 

 As I have before pointed out (Anat. Anz., xi, 8, 1895, p. 255), 

 the Already extensive literature which treats of the anatomical 

 uses of formaldehyde is much confused by inaccurate use of 

 these terms ; many writers use them indiscriminately. It is 

 frequently impossible to discover from the statements of an 

 author whether he means such or such a percentage of formal- 

 dehyde, or such or such a percentage of the commercial 40 per 

 cent, solution employed by him, the one being of course two 

 and a half times stronger than the other. All that can be 

 said is, that the majority of authors seem to quote in 

 percentages of the commercial solutions. I think it must be 

 admitted that the proper way of stating the strengths of these 

 solutions is either to state them in terms of formaldehyde, 

 and say so, or to say "formol, or formalin, diluted with so 

 many volumes of water." The present confusion is most 

 inconvenient. 



