76 STUDYING MOLDS, YEASTS, AND ACTINOMYCETES 



pus, stain both cells and fungus elements, and make them more 

 translucent. Another solution consists of 



In examining pus or sputum for fungi, beginners are apt to mistake 

 fat droplets for yeast cells and elastic tissue fibers for mycelium. 

 Fat droplets are highly refractile, and sometimes the edge may ap- 

 pear to be doubly contoured. Adjacent large and small droplets may 

 look like a budding cell. Elastic tissue fibers vary in diameter and 

 branch like mycelium. In both cases, however, there is no internal 

 strycture. Both fat droplets and elastic tissue fibers appear clear 

 and homogeneous, whereas both yeast cells and mycelium will show 

 internal vacuoles and granules. Myelin globules are present in large 

 numbers in some specimens and may be mistaken for yeasts or 

 hyphae. 



Microscopic Examination of Hairs and Scales. In the diagnosis 

 of dermatophytosis the microscopic examination of hairs and of 

 scales of epidermis is of first importance. Here again the standard 

 procedure is to mount the hairs or scales in a strong alkaline solution 

 to soften the material so that it may be flattened under a cover slip, 

 and to make it translucent so that the fungus elements may be seen. 

 It is important to select hairs which appear to be infected, preferably 

 the stumps of hairs which have broken ofT. The fungi will be found 

 near the root of the hair. The use of ultraviolet light may be help- 

 ful in selecting infected hairs. With both hairs and scales of epi- 

 dermis, it is best to collect material from just back of the advancing 

 border of the lesion, where fungi may be expected to be most abun- 

 dant. 



The examination of hairs and scales mounted in strong sodium 

 or potassium hydroxide presents all the disadvantages mentioned 

 under the examination of exudates, and additional ones because the 

 alkali may give rise to artifacts that can be mistaken for fungi — 

 crystals of the alkali where evaporation has taken place under the 

 cover slip, and the mosaic fungus. The latter consists of an irregu- 

 lar, branched filamentous structure, without internal granules or 

 vacuoles, that appears in some scales of epidermis when treated with 

 strong alkali. The exact nature of the artifact is unknown. First 

 described by AVeidman,** the mosaic fungus has been further studied 

 by Davidson and Gregory ^ who suggested that it is made up of 

 cholesterin crystals, by Dowding and Orr,^ and by Swartz and 



