284 An Introduction to Medical Mycology 



(a) Clinical characteristics.— As a rule there is little inflammatory 

 reaction in the scalp. Several patches of apparent alopecia are usually noted 

 which, on close inspection, are seen to contain broken-off, stubby hairs. 

 This is the so-called "gray patch" ringworm. The stubs may be colorless 

 and may be extracted with very slight traction. Besides the larger areas, 

 smaller areas, in which only a few hairs are involved, are frequently de- 

 tected in routine examinations under filtered ultraviolet rays. Occasionally 

 there is an inflammatory reaction in the scalp. Pustulation is uncommon 

 and kerion formation rare, although it has been noted. Ringed, slightly 

 inflamed lesions may be present on the smooth skin, particularly if the 

 patient also has tinea capitis. Other parts of the body, such as the hands, 

 feet and nails, are not affected. 



(b) Immunologic reactions.— Occasionally children with infection due 

 to M. audouini have moderate reactions to the intracutaneous test dose of 

 trichophytin. More frequently the reaction is slight or absent; in only a 

 few instances have we observed strong reactions. 



(c) Microscopic features.— The fungus appears in the form of a mosaic 

 sheath around stubby hairs. There is little tendency to chain formation. The 

 individual elements, or spores, are round and small. In infections of the 

 glabrous skin, mycelium may be detected. Lanugo hairs may occasionally 

 be infected. 



(d) Cultural characteristics.— Beginning as a white feathery fluff, 

 the colony grows moderately into a grayish-white fluffy culture. The aerial 

 growth is scanty. There is usually a central elevation. Radial grooving may 

 appear, especially on Petri dishes, but this is not constantly or even fre- 

 quently found on dextrose agar. On maltose agar the formation of radial 

 grooves is one of the chief characteristics. Secondary radial grooves may 

 also form. Pleomorphism is uncommon. 



(e) Culture mount.— Fuseaux are only occasionally found. Microconidia 

 are present in limited numbers. Chlamydospores and pectinate bodies are 

 frequent; they are more readily observed when corn meal agar is used. 



(f) Filtered ultraviolet rays.— The short, stubby hairs found in the 

 patches of tinea capitis fluoresce as bright, clear green dots. All the hairs in 

 a lesion are usually seen to be involved. The cultural growth in 10 days is 

 dull, clear and mouse-gray throughout. 



(g) Animal inoculation.— Animals are resistant to infection with this 

 fungus. 



(h) Differential diagnosis.— The direct examination of an infected hair 

 will show Microsporum if it is present, since the spores are small, occur in 

 large numbers and have a mosaic arrangement outside the hair shaft. On 

 culture M. audouini may be differentiated from M. lanosum because M. 



