40 FIXING AGENTS. 



follows that one-third alcohol contains, approximately, 29*9 per 

 cent, of absolute alcohol (or very nearly 30, and not 33' 3, as 

 was stated by a most regrettable oversight in the 1st edition). 

 (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- car mine, 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. 



62. Absolute Alcohol. This is also a very valuable reagent. 

 It preserves very well the structure of the 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 objects 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 

 hydrates on exposure to air. Fol recommends that a little quicklime be 

 kept in it. This absorbs part at least of the moisture drawn by the alcohol 

 from the air, and has the further advantage of neutralising the acid that is 

 frequently present in commercial alcohol. 



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

 in it. It is stated that by this means ordinary alcohol may be rendered 

 absolute. 



Ranvier adopts the following plan for preparing an alcohol absolute enough 

 for all practical purposes. 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, 



