FIXING, IMBEDDING, AND STAINING 49 



with a solution of eosin. A J per cent aqueous solution will suffice, 

 but alum eosin (1- per cent alum) is even better. Unless the object 

 is first killed, as by being treated with acid, the stain will very 

 readily disappear, or become indistinct, when mounted in glycerin 

 "or in glycerin jelly. A J- per cent solution of fuchsin may also be 

 used. Hyaline fungi to be preserved as glycerin preparations 

 should always be stained, otherwise the fungous outlines will in 

 time become very indistinct. 



Many of the fungi may be carefully studied for purposes of 

 identification and for a knowledge of their general structure with- 

 out the use of stains and staining methods. To this class belong 

 practically all of the filamentous fungi which are not hyaline, that 

 is, those which are flavous, olivaceous, brown, or otherwise colored 

 in such a way that the outlines of cell walls show distinctly when 

 mounted in water, glycerin, glycerin jelly, etc. The most delicate 

 fungi are those which necessitate the use of stains, such as many 

 members of the Mucoracece, Saprolegniacece, Peronosporacece, and 

 other related orders, as well as many mucedinous Hyphomycetes. 



It is usually recommended to make up concentrated alcoholic 

 solutions of eosin and fuchsin as stock solutions. Then, as desired, 

 weaker stains may be prepared from the above by dilution with 

 water, the latter, of any strength desired, being kept conveniently 

 in dropper bottles. The staining process is very simple and con- 

 sists merely in adding a drop or two of the stain to the preparation 

 on the slide, then washing it off with water when the desired effect 

 has been produced. A drop or two of low-grade or acidulated alco- 

 hol will usually remove any overstaining. 



It has been ascertained that those fungi which are stained only 

 with difficulty by this process are much more readily stained if an 

 acid or an alkaline solution of the stain is employed. Carbol fuchsin 

 is one of the recognized strong stains of this class. This may con- 

 veniently consist of a .5 per cent aqueous solution of carbolic acid, 

 to which is added sufficient of the concentrated fuchsin stock 

 solution to make a strong stain. 



Fleshy fungi and tissues. Staining processes such as have been 

 already described are very simple when compared with most of 

 those which must be resorted to when the material consists of a 

 fungous tissue, or of other tissue penetrated by a fungus. Loose, 



