FIXING AND HAKDHNLNG AGENTS. 71 



often indicated. Absolute alcohol is seldom advisable. You 

 ought to beg-in with weak, and proceed gradually to stronger, 

 alcohol. Large quantities of alcohol should be taken. The 

 alcohol should be frequently changed, or the tissue should 

 be suspended near' the top of the alcohol, in order to have 

 the tissue constantly surrounded with pure spirit (the water 

 and colloid matters extracted from the tissue falling to the 

 bottom of the vessel). Many weeks may be necessary for 

 hardening large specimens. Small pieces of permeable 

 tissue, such as mucous membrane,, may be sufficiently 

 hardened in twenty-four hours. 



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

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

 alcohol, or RANVIEK'S ALCOHOL, known in France as " Alcool 

 au tiers/' which is the name given to it by Ranvier himself ; 

 in Germany as " Drittelalcohol " or " Eanviersche alcohol 

 dilutus ; " in Italy as " alcool al terzo." It consists of two 

 partx of water and one part of alcoJiol of 90 per cent, (and not 

 of absolute alcohol, as was stated by an oversight in the first 

 edition -an error which I have seen copied in more than 

 one place). See the Trait e Technique of Ranvier, p. 241, et 

 passim. 



According to Ranvier, care should be taken that the 



O ' 



alcohol is of the strength specified, as the effects of this re- 

 agent depend, he states, to a remarkable degree on its 

 strength. 



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

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

 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. 



101. Absolute Alcohol. This is sometimes valuable on 

 account of its great penetrating power, being, indeed, one of 

 the most penetrating of known fixing agents. Mayer finds 

 that boiling absolute alcohol is often the only means of killing 



