240 SPECIFIC MICRO-ORGANISMS 



yellow crust with depressed center, the "Scutulum.'" By macerat- 

 ing this crust in 50 per cent antiformin the elements of the 

 mold are made clearly visible under the microscope. In the 

 center of the lesion are doubly contoured oval or rectangular 

 conidia 3 to 8/* by 3 to 4//, single and in chains. The mycelial 

 threads are indistinguishable in the center, but are seen at the 

 periphery as tubes of very irregular width, refractive with granu- 

 lar protoplasm, often branched or knobbed at the end. The 



FIG. 97. Typical scutulum of favus in a mouse. (After Plant.) 



scutulum in its interior is a pure culture of the mold, entirely free 

 from other organisms. The mold also grows in the interior of 

 the hair shaft, and by macerating the hair in alkali the fungus 

 may be demonstrated microscopically. 



Cultures may be obtained upon various media. Plaut recom- 

 mends a medium containing pepton i to 2 per cent, glycerin 

 0.5 per cent, salt 0.5 per cent and agar 2 per cent, without meat 

 extractives or any addition of alkali. The cultures are incubated 

 at 30 C. Mycelial threads and numerous conidia are produced. 



Inoculation into the epidermis of mice or onto the human 



