442 



MEDICAL MYCOLOGY 



distinguished, from impetigo by the long duration in the same place, by the 

 beginning of a scar, and by the favic hairs caught in the crust. 



While the hair is as important as the scutulum in diagnosis, its infection 

 is not evident in the early stages. Infection occurs in the root and the fungus 

 must grow up through the hair to a height above the scutulum before changes 

 in the hair are visible. This process takes 3-4 months, after which the hair 

 shows a characteristic appearance for several years until finally it is expelled 

 by scar formation in the follicle. The hair is a dull, powdery gray, and dry, 

 quite different from a hair normally becoming white with age, and its length 

 rarely exceeds a few centimeters. While it is a little more fragile than normal 

 hair, it is not so fragile that one is unable to epilate it. When the hair is 

 crushed, it readily splits longitudinally like the strands of retted hemp. In 

 microscopic preparations, the fungus is absent from the bulb. Tiny air bub- 

 bles adhere to the surface of the hairs and long slender ones are seen within 

 it, probably because of infiltration of air into the spaces left by the dead 



Fig. 75. — Section through hair from a case of favus, caused by AcJiorion Schoenleini, 

 showing mycelium and air spaces in the hair, as well as attached air bubbles. (After Sabouraud 

 1910.) 



hyphae (Fig. 75). It is possible that this is what gives the hair its gray color. 

 There are relatively few hyphae in any one hair, so that the structure of the 

 hair is always clearly visible between them. These hyphae are flexuous and 

 wavy, somewhat variable in diameter, dichotomous with the branches growing 

 downward toward the bulb, the older portions farthest from the bulb, the 

 region of active growth being where the hair passes the horny layer, never 

 in the depths of the follicle or in the bulb. Sometimes the hyphae are slender 

 enough to suggest those of EctotncJiophyto7i, but they never produce any spores 

 outside the hair. 



In very old cases, the aspect of the lesions changes very much, appearing 

 as rows of folliculites surrounding a scar alopecia. At first the scars appear 

 as isolated points between active lesions still covered by scutula, which di- 

 minish in size and disappear. The follicle occupied by an infected hair is 

 marked only by a persistent red point. Increasingly the scar areas appear 

 and become confluent, leaving islets of healthy hair and hair in the early stages 



