62 cJIAJ'TEli V. 



Another plan that I have seen recommended is to suspend strips of 

 gelatin in it. But it is probably rendered very acid thereby. 



Ranvier prepares a sufficiently "absolute " alcohol as follows: Strong 

 (95 per cent.) alcohol is treated with calcined cupric sulphate, with which 

 it is shaken up and allowed to remain for a day or two. It is then 

 decanted and treated with fresh cupric sulphate, and the operation is 

 repeated until the fresh cupric sulphate no longer becomes conspicuously 

 blue on contact with the alcohol ; or until, on a drop of the alcohol 

 being mixed with a drop of turpentine, no particles of water can be 

 seen in it under the microscope. The cupric sulphate is prepared by 

 calcining common blue vitriol in a porcelain capsule over a flame until 

 it becomes white, and then reducing it to powder (see Proc. Acad. Nat. 

 Set. Philad., 1884, p. 27; Journ. Roy. Mic. Soc., 1884, pp. 322 and 984). 



Test for the presence of water (TvoN, C. R. Acad. Set., 1897, p. 1181). 

 Add coarsely powdered calcium carbide ; the merest trace of water will 

 cause an evolution of acetylene gas, and on agitation the alcohol will 

 become turbid. 



104. One-third Alcohol. The grade of weak alcohol that is 

 generally held to be most useful for fixing is one-third 

 alcohol, or RANVIER'S ALCOHOL. It consists of two parts of 

 water and one part of alcohol of 90 per cent, (and not of 

 absolute alcohol). See the Traite Technique of Ranvier, 

 p. 241, et passim. 



Objects may be left for twenty-four hours in this alcohol; 

 not more, unless there be no reason for avoiding maceration t 

 which will generally occur after that time. You may con- 

 veniently stain with picro-carmine, alum-carmine, or methyl 

 green. 



This reagent is a very mild fixative. Its hardening action 

 is so slight that it is not at all indicated for the fixing of 

 objects that are intended to be sectioned. Its chief use is 

 for extemporaneous and dissociation preparations. 



105. Acid Alcohol (MAYER, Mitth. Zool. Stat. Neapel, ii, 1881, p. 7). 

 To 97 vols. of 90 per cent, alcohol add 3 vols. pure hydrochloric (or 

 nitric) acid. Wash out with 90 per cent, alcohol. 



The use of this mixture is principally for the preparation of museum 

 specimens. 



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

 cent, alcohol with 5 per cent, of hydrochloric acid. 



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

 (by A. DE SOUZA). It hardens, dehydrates, and clears at the same time. 

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

 brain. See Comptes Rendus liebd. de la Soc. de Biologic, 8 ser., t. iv, 

 1887, p. &1 



