184 INFECTIONS CAUSED BY MOLDS 



scopic examination of such a colony sliows many cells which closely 

 resemble those found in tissue, others which are perhaps twice as 

 long as thick and divided into two cells by a central septum, and 

 some which form thick, abortive hyphae. An examination of these 

 types and transitional forms illustrate clearly the morphological dif- 

 ferences between the budding cells of Blastomyces dermatitidis and 

 those of the true yeasts. 



When pus containing the fungus is streaked on Sabouraud agar 

 and incubated at room temperature or 30° C. the parasitic growth 

 phase produces branching hyphae and the resultant colony is that 



of a mold. Three types of growth 

 have been described. Colonies 

 may be somewhat friable (the so- 

 called mealy type) , they may con- 

 sist of a glabrous moist growth on 

 the agar surface with coremia 

 (upright composite strands of hy- 

 phae forming spine-like aggregates 

 at the center of the colony), or 

 they may be tangled masses of 

 dry, aerial hyphae. Some colonies 

 are pure white whereas others be- 

 FiG. 93. Blastomyces dermatitidis. p^j^g brown in age. These varia- 

 Conidia in culture. ^-^^^ ^^^ sometimes related to 



strain differences and may also be observed in a single strain when it 

 is kept in the laboratory over a period of years. Thus the mealy 

 type is most apt to appear in newly isolated strains and microscopic 

 examination will show the presence of pseudobudding forms and 

 abortive hyphae. The presence of contaminating bacteria which 

 may be carried along undetected for many culture generations often 

 modifies the growth habit. 



Conidia. Gilchrist and Stokes,'^ in their original description of 

 the fungus, and many subsequent observers have described the 

 conidia which develop in cultures. These structures are quite vari- 

 able in size and shape, depending to some extent upon the individual 

 strain. They are spherical to pyriform or oval and range in size 

 from 2 microns in diameter to 3.5 by 5 microns. Some are sessile, 

 budding directly from the hyphae, and others are on lateral stalks of 

 conidiophores 1 to 10 microns long. The walls are smooth. Conidia 

 may be rare, and in strains kept for many years in the laboratory 

 none may be found. 



