TRICHOPHYTONEAE 441 



lupinosa, tinea Iwpinosa, etc. It is lenticular in shape with a depression above. 

 The hyphae and spores which compose it, form a ring about the follicular 

 orifice in the thickness of the horny layer of the epidermis. This ring, scarcely 

 visible at first, often attains the size of a pea or even greater. It occurs only 

 about a follicular orifice and begins as a flat intraepidermic pustule, which 

 contains white pus, due to the infiltration of leucocytes. At the base of the 

 pustule is a yellow disc, the beginning of the true scutulum. This stage is 

 rarely observed, for it soon disappears. As the scutulum grows, it assumes 

 the form of a convexoconcave meniscus, then its upper face becomes umbili- 

 cate, and its diameter increases. The horny layer exfoliates, often taking some 

 of the upper portion of the scutulum with it. This allows the disintegration 

 of the upper portion of the scutulum, composed of dead leucocytes, giving it 

 the umbilicate appearance. The scutulum now consists of an agglomeration 

 of mycelium in a considerably enlarged hair follicle, surrounded below by 

 leucocytes and their remains. It consists of three zones : the inner, surround- 

 ing the hair, is made up of a tangled mass of mycelium breaking up into 

 arthospores; the middle zone of regular hyphae separated by portions of the 

 horny layer of the epidermis ; and the outer zone composed of hyphae perpen- 

 dicular to the surface of the scutulum with some infiltrated leucocytes in the 

 outermost portion. At the surface of the scutulum, the epidermis is intact, 

 while the dermis below is somewhat infiltrated and sclerosed as in most lesions 

 following chronic irritation. Sometimes the scutula remain small and distinct 

 (favus urceolaris) or spread and partially coalesce (favus scutiformis) or 

 agglomerate into heaps (favus squarrosus). Sometimes they form a flat crust, 

 superficially resembling impetiginous or seborrheic lesions, but if this is par- 

 tially rubbed off, the sulphur yellow lower portions of the scutula may still 

 be seen. Cases of several months' standing develop a characteristic odor, 

 similar to that of a mouse nest. 



The very small scutula of some cases of favus are usually overlooked, 

 while in some cases of the impetiginous variety they are not found. The 

 pityriasiform type has few scales which may be large and of variable form. 

 Under the scales, the bottom of the lesion is red, similar to that of psoriasis, 

 with a surface of small thin yellowish scales. The superficial scales are easily 

 detached while the deeper ones, in contact with the hair, are adherent, and 

 cover a dry surface. Such lesions might easily be mistaken for pityriasis, dry 

 eczema, or psoriasis, were it not for the dry, gray, discolored hairs on the sur- 

 face, which are also typical of favus. A close search in these lesions will show 

 very small scutula, about the size of a pinhead. Almost always in old affec- 

 tions small scar alopecias may be found. The mouse-gray surface of the hair, 

 which offers little resistance to traction, is also characteristic. These lesions, 

 being of long duration, spread very slowly but never diminish. They are 

 relatively more common among the Moslem population of Algeria than in 

 Western Europe (Catanei 1933). 



In the impetiginous type, there are only two or three small lesions covered 

 by an amber yellow fragile crust. Since no scutula are visible, it may be 



