58 STUDYING MOLDS, YEASTS, AND ACTINOMYCETES 



cide and to collect material from the active border of the lesion. 

 Scales or the roofs of vesicles can be removed with sterile scalpel or 

 scissors. They can be placed directly upon the surface of agar slants 

 but, especially in dermatophytosis of the foot, isolation of a pure 

 culture is easier if the specimens are placed first in a sterile Petri 

 dish, cut in small pieces with sterile scalpel, and flooded with 70 

 per cent alcohol. After exposure for 2 minutes, transferring the 

 pieces to agar slants is begun and the procedure is timed so that the 

 last specimens planted have been in the alcohol about 8 minutes. 

 The 70 per cent alcohol, being more bactericidal than fungicidal, 

 exerts a selective action and permits the isolation of a pure culture 

 of the fungus without bacterial contamination. 



In the isolation of dermatophytes when Staphylococcus and other 

 bacteria may be present on the specimen, the latter should be laid 

 carefully upon the unbroken agar surface at the point where it first 

 touches. The fungus hyphae need no encouragement or aid to pene- 

 trate the agar. Rubbing the specimen across the surface of the agar 

 and breaking the surface of the agar both increase the area over 

 which contaminating bacteria will be deposited and if these bacteria 

 are alive their growth will interfere with the development as well as 

 the isolation of the fungus. If bacteria or saprophytic fungi grow 

 in the primary culture with the pathogen, the latter can be isolated 

 by transferring with a sharp stiff needle some of the conidia or aerial 

 hyphae after they grow beyond the contaminants. 



Most of the fungi pathogenic for man can be isolated in culture 

 by the simple method of streaking or spreading pus, sputum, blood, 

 macerated tissue, or other pathological material on the surface of 

 Sabouraud agar slants. Usually no preliminary digestion on con- 

 centration is desirable or necessary. A few pathogens require special 

 treatment and these exceptions will be briefly noted here. Actinomyces 

 bovis will not grow on Sabouraud's agar; pus containing this fungus 

 should be planted on veal infusion agar containing 1 per cent glucose. 

 Brewer's thioglycollate glucose medium, or blood agar and incubated 

 anaerobically. Pityrosporum ovale will grow on Sabouraud's agar 

 or similar medium only if it is first covered with a thin layer of 

 lanolin or other fat. A few of the pathogens will grow poorly on any 

 media yet devised and are therefore very difficult to isolate in culture. 

 The separation of pathogenic molds from bacteria is often a diffi- 

 cult problem. In many cases bacteria are much more numerous than 

 the fungi. Here success in isolation is in proportion to the number of 

 cultures made. If a dozen or more slants are inoculated, one has a 

 much better chance of obtaining a pure culture than if he merely 



