FIXING, IMBEDDING, AND STAINING 43 



Corrosive sublimate. Corrosive sublimate is always an excellent 

 killing and fixing agent for histological staining. It may be used as 

 a concentrated aqueous solution, to which, also, the addition of about 

 i per cent of acetic acid is often helpful. Whether the material is 

 a fleshy sporophore, or a piece of host tissue penetrated by hyphae, 

 it should remain in this fixing agent for about twenty-four hours, or 

 until the tissue is distinctly white-opaque. The material is washed 

 for an hour or two in water, and then carried through the grades of 

 alcohol, 30, 50, and 70 per cent, and eventually stored in 65-75 

 per cent. If not immediately imbedded, it is well to change the 70 

 per cent alcohol several times in order better to remove the subli- 

 mate. Sometimes it is necessary to add a little tincture of iodine 

 to the alcohol in order to more thoroughly remove the corrosive 

 sublimate. If this is done, the liquid should be changed as often 

 as it is discolored by the material. It is also claimed that after cor- 

 rosive sublimate the material should not long be stored in alcohol, 

 as such material will readily become brittle. 



It is often preferable with fungous tissue to use a concentrated 

 solution of the sublimate in 96 per cent alcohol, to which it may 

 also be well to add I per cent acetic acid. This mixture penetrates 

 more readily and is more valuable for cytological work than the aque- 

 ous solution. Objects thus fixed are transferred after from a few 

 minutes to twenty-four hours to lower grades of alcohol, and wash- 

 ing may be effected by a few changes at the grade used for storage. 



At laboratory temperatures mercuric chloride is soluble in water 

 to the extent of about 5 to 6 per cent, and it is much more soluble 

 in alcohol. If it is desired to use stronger solutions of the mer- 

 curic salt, it will be necessary to add to the solution some chloride, 

 such as sodium or ammonium. As will be seen later, both the car- 

 mine and anilin stains may be used after corrosive sublimate, and 

 the mixtures of this agent are especially good for fixing parts of 

 any of the fleshy fungi. 



Chromic acid and chrom-acetic acid. Solutions of chromic acid 

 from .5 to i per cent are sometimes used for fixing fungous mate 

 rial ; but in general it is so much less valuable alone than in 

 combination with acetic acid of less or equal strength that the com- 

 bination should be employed. Wash and dehydrate as for the next 

 fixing agent. 



