42 FIXING AGENTS. 



rosive sublimate, chromic acid or nitric acid) by greatly 

 enhancing their penetrating power; 70 per cent, is a good 

 grade for this purpose. 



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

 found generally useful for fixing is one third alcohol, or 

 RANVIEK'S ALCOHOL, known in France as " Alcohol au tiers/' 

 which is the name given to it by Ranvier himself; in Ger- 

 many as " Drittelalcohol " or " Ranviersche alcohol dilutus ;" 

 in Italy, as " alcool al terzo." It consists of two parts of water 

 and one part of alcohol 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 Traite Technique of Ranvier, p. 241, et passim. 



Care should be taken that the alcohol is of the strength 

 specified, as the effects of this reagent depend to a remark- 

 able 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 classical reagent is a very mild fixative. Its harden- 

 ing action is so slight that it is seldom indicated for the fixing 

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

 for extemporaneous and dissociation preparations. 



Absolute Alcohol. This is also a very valuable reagent It 

 preserves very well the structure of nuclei, which is by no 

 means the case with one-third alcohol. It has over the latter 

 also the advantage of superior 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 certain Arthropoda rapidly enough to avoid 

 maceration brought about by the slowness of penetration of 

 common cold alcohol (especially in the case of Tracheata) . 



It is important to employ for fixing a very large proportion 

 of alcohol. Alum-carmine is a good stain for small specimens 

 so fixed. For preservation, the object should be put into a 

 weaker alcohol, 90 per cent, or less. 



Absolute alcohol is found in commerce. It is a product that it is almost 

 impossible to preserve in use, on account of the rapidity with which it 



