372 SOME HARDENING AGENTS. 



some action on the tissues at present unknown, but which renders 

 after-staining useless and impossible in most instances. Corrosive 

 sublimate and picric acid can be washed out, and you may use 

 any stain afterwards. 



If anyone will take the trouble to examine the literature on the 

 subject of hardening, they will be greatly surprised at the diversity 

 of opinion among original workers. It should be remembered 

 that most of our text-books are simply re-copies of the older 

 works, and which, coming to the front now that microscopy is 

 more studied, are often looked upon as new methods. It seems 

 to me that if we would consider hardening agents, we should take 

 one re-agent at a time and try hardening every part of the body in 

 it ; then make sections, stain, mount, and study the changes by 

 comparison, and having taken one re-agent as a standard we ought 

 to be able to come to some definite conclusions as to their relative 

 manner of acting on the tissues. 



One authority says : — " We should never use weak and increas- 

 ing grades of alcohol to harden with, but always use absolute 

 alcohol." I do not doubt but that if we could afford the expense 

 and be certain of our agent, we should never use anything but 

 absolute alcohol, and then the purest sample known, and never 

 the diluted variety or proof spirit, as the latter, in addition to its 

 admixture with water, is almost always contaminated with other 

 substances, and often exhibits an acid reaction. If we desire to 

 use diluted alcohol, we should mix the absolute variety with the 

 requisite quantity of distilled water to obtain a reliable result. 

 Personally, I have never had any occasion to find fault with the 

 ordinary alcohol ; and, except in cases of celloidin and other 

 embedding agents, and to demonstrate Heidenhain's experiments 

 on epithelium, etc., I never have had to use absolute alcohol in 

 micro work, and I do not think it is necessary. 



It seems to me that if we are going to consider alcohol of any 

 grade as d. first-class hardening agent, it ought to stand a fair test — 

 namely, that of a general hardening agent, but particularly should 

 it be tested with the most delicate structures, for we can then easily 

 appreciate the sudden changes which will take place in such tissues 

 compared to those which are more resistant. We usually look on 

 the nervous system and the eye as being the most delicate parts of 



