FIXING, IMBEDDING, AND STAINING 45 



material. The decolonization is best effected when the material is 

 in 70 per cent alcohol, and during the dehydration process. The 

 simplest method is to add to three parts of 95 per cent alcohol one 

 part of hydrogen peroxide and allow the material to stand in this 

 mixture from twelve to twenty-four hours. It seems to be less 

 injurious to decolorize in mass than eventually to decolorize the 

 sections on the slide, just prior to staining. 



Alcoholic mercuro-nitric acid solution. This fluid should be 

 more generally employed with the fungi, since it penetrates well, 

 and may be advantageously followed by haematoxylin, anilin, and 

 carmine stains. Gelatinous masses of spores remain intact fairly well 

 in this. About 300 cc. may be conveniently made up as follows : 



Water 270 cc. 



96 per cent alcohol .... 30 cc. 



Glacial acetic acid .... ar cc. 



Nitric acid 5 cc. 



Corrosive sublimate ... 10 grams * 



Material should remain in this agent from one to six hours, then 

 it may be passed through grades of alcohol to 70 per cent, where 

 several changes of the liquid should be made. 



I have not found picric acid, or combinations of this with mer- 

 curic chloride and other agents, satisfactory for work with the fungi. 



Formalin is, of course, a good general preserving liquid, but it is 

 not practicable when imbedding methods may afterwards be 

 employed. 



II. THE PARAFFIN PROCESS: INFILTRATION AND 

 IMBEDDING 



Material which is to be sectioned by means of the microtome is 

 now far more commonly imbedded in paraffin than in celloidin or 

 collodion. Some chief advantages claimed for the paraffin method 

 are : ( I ) better penetration of the imbedding substance, permitting 

 more uniform and thinner sections ; (2) facility in cutting, together 

 with ease of preserving the sections in serial order ; (3) convenience 

 of the paraffin ribbon in the further processes involved. 



Assuming that the substance which is to be imbedded is stored 

 in alcohol, it becomes necessary, as the first step, to dehydrate 

 thoroughly by treating with 90 per cent alcohol during about twelve 



