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MEDICAL MYCOLOGY 



The second most clearly distinguished type of lesion of the hair is that 

 of tinea tonsurans, in which the infected hairs are so weakened that they break 

 off a few millimeters above the scalp, leaving an area which looks as if the 

 hair had been clipped or shaved, hence the name. Two genera of fungi are 

 responsible for this condition and since clinical details vary in many respects 

 in the two genera, they will be discussed separately. 



In the first type, that caused by species of Microsporum, the hair breaks 

 three or four millimeters from the skin and is surrounded by a thin white 

 sheath of fungus spores, 2-4/x, in diameter, packed closely together without 

 apparent order. Generally the lesion is covered with a layer of gray scales. 

 It begins as a small erythematous spot whose circular border is scarcely redder 

 than the center. At first the hair appears normal. In a few days the lesion 

 pales and becomes furfuraceous, while the hair begins to show its character- 

 istic appearance. Each hair is incased at its base for about 3 mm. by a grayish 

 white sheath, which seems to be a prolongation of the follicular epidermis 

 (Fig. 76). A little later the hairs break and the white lamellar scales appear. 

 Practically every hair in the lesion is attacked, in strong contrast to lesions 



Fig-. 76. — Section through hair from a case of tinea tonsurans microsporica, caused by a 

 species of Microsporum. (After Sabouraud 1910.) 



caused by Trichophyton in which many normal hairs are found within the 

 infected area. Unless treatment has intervened, the infected hairs become 

 grayish, discolored, and are very easily epilated. Sometimes the lesions re- 

 main dry; in other cases they gradually take on a seborrheic appearance when 

 the scales agglomerate in a thick layer of a yellowish color and greasy con- 

 sistency. The hairs become embedded in this mass. The maximum diameter 

 of an infected area is 4-6 cm. The infection, however, may be carried by a 

 broken hair to a new spot by autoinoeulation. This may be repeated until 

 five or six lesions have been formed. As these spread they may coalesce, 

 usually leaving triangles of uninfected hairs. Earely many lesions may form 

 by autoinoeulation until most of the scalp is invaded. When a lesion stops 

 spreading, the vitality of the fungus seems to be exhausted and it is rarely 

 capable of further autoinoeulation. Careful epilation at this stage will usually 

 remove the bulb with the hair, and if new hair grows, it will be uninfected. 

 Sometimes the infected hairs are gradually shed and after a variable time, 

 lanugo appears on the denuded surface and then normal hairs grow. This 

 denuded state is to be differentiated from a similar state which other types 



