74 STUDYING MOLDS, YEASTS, AND ACTINOMYCETES 



ing the agar containing the colony under a cover slip, and examin- 

 ing directly. 



Microscopic Examination of Tissues and Exudates. The diagnosis 

 of fungus diseases of man depends upon direct microscopic examina- 

 tion of tissues and exudates as well as upon cultural methods. In 

 some cases the fungi grow so scantily that, if they are not abundant 

 enough to be found on microscopic examination, it is not likely that 

 they will overcome the competition of contaminants and grow in 

 cultures. In sporotrichosis, however, the small size of Sporotrichum 

 and the difficulties of differentially staining it make its isolation in 

 culture the preferred method of laboratory diagnosis. In all cases, 

 when possible, it is desirable to isolate pathogenic fungi in culture 

 because the final identification of the fungus depends upon deter- 

 ' mination of its characters in artificial culture media. The specific 

 methods of examination and the appearance of the fungus will be 

 discussed in detail in the consideration of the various mycoses. 



In searching for yeasts, molds, and actinomycetes in pus or other 

 exudates or tissues from infections in man and animals, certain gen- 

 eral facts must be kept in mind. Where it is possible to obtain pus 

 from abscesses which have just been opened surgically before they 

 have formed a fistula communicating with the exterior, it is usually 

 relatively easy to find the organisms. After they have broken open, 

 however, there is always an extensive secondary infection with bac- 

 teria, and it is often almost impossible to find the fungi. In cases 

 where the parasites cannot be obtained in the pus draining from the 

 abscess, they may be found in sections of tissue removed from the 

 wall of the abscess. A biopsy is thus frequently of great diagnostic 

 value. 



Fungi may be demonstrated in sections of tissue by the Gram- 

 Weigert method or one of its various modifications. Unna *- has 

 described a modification of the Unna-Pappenheim stain which is said 

 to give a very clear picture, especially in skin sections. The sec- 

 tions are removed from water and stained for 5 to 10 seconds in the 

 following solution. 



Pyronin 0.9 gram 



Methyl green 0.1 gram 



Alcohol (96 per cent) 9.0 ml. 



Glycerol 10.0 grams 



Aqueous phenol (3^ per cent) to 100.0 ml. 



These sections are then rinsed in water and quickly dehydrated in 

 absolute alcohol, cleared in xylol, and mounted in balsam. Fungus 



