THE YEASTS 633 



thionin, methylene-blue, or the polychrome stains. In fresh prepara- 

 tions the addition of a little NaOH in weak solution facilitates the 

 search. When found, the organisms are easily recognized by their size, 

 their highly refractive doubly-contoured cell-membrane, their vacuolated 

 protoplasm, and, most important, by the discovery of budding forms. 

 In tissue sections they are recognizable by the ordinary hematoxylin- 

 eosin technique, but may be better demonstrated by the Loeffler methy- 

 lene-blue method in use for bacterial tissue-staining. Excellent prep- 

 arations are obtained by staining frozen sections with thionin, a method 

 well adapted for the demonstration of capsules. 



The cultivation of the blastomycetes is comparatively easy after 

 they have once been obtained in pure culture. Their isolation, however, 

 usually is difficult when they occur in material contaminated with bac- 

 teria. Growing more slowly than the bacteria, cultures taken from such 

 contaminated material usually show very few yeast colonies. No special 

 methods of facilitating the procedure have been devised, but success 

 will often attend painstaking and oft-repeated plating of the mixed 

 cultures in high dilution. The most favorable medium for this process is 

 glucose agar. When once obtained in pure culture, the blastomycetes 

 can readily be kept alive for indefinite periods by transplantation re- 

 peated every two or three months. On agar or glucose agar, colonies 

 appear after about three or four days as minute, glistening, white 

 hemispherical spots which are not unlike colonies of staphylococcus 

 albus. Planted in agar stab cultures, the microorganisms indicate 

 their preference for a well-oxygenated environment by growing but 

 slightly along the course of the stab, but by heaping up in a thick, 

 creamy layer upon the surface of the medium. This layer in old. 

 cultures may be a quarter of an inch high. At first white, the 

 growth, after three or four weeks, may turn distinctly yellow or even 

 brown. In broth, the microorganisms form a stringy, gelatinous, and 

 uneven cloud. On Loeffler 's blood-serum media, and upon gelatin, 

 growth is easily obtained. The gelatin is not liquefied. Sugar media 

 are fermented, by few of the pathogenic blastomycetes, a fact which 

 places them rather in distinct contrast with the fermenting yeasts used 

 in the industries. 



Great and fundamental differences seem to exist between the patho- 

 genic species described by various observers, and attempts at system- 

 atizing the various members of the group, such as that by Rickets, 1 



Rickets, Jour. Med. Res., 6, 1902. 



