THE MOULDS. 219 



essentially in circular scaly formations surrounding the hairs, 

 and eventually causing the latter to fall out. 



Favus. Tinea favosa, caused by the Achorion Schonleinii, 

 is a contagious skin disease, occurring usually on the scalp 

 and characterized by cup-shaped yellow crusts perforated by 

 hair. The " favus cup," or scutulum, is characteristic. 



Morphology. The Achorion Schonleinii consists of slender 

 raycelial threads which may contain spores. The threads are 

 broader and the joints more numerous than in ringworm. 

 The spores are highly refractile and measure 20 to 40 P. in 

 length. For examination staining is unnecessary, though 

 easy. A piece of the scutulum, or crust, or the hair-bulb is 

 examined in a drop of liquor potassae. 



Biologic Character. It grows readily on all culture-media, 

 best on acid agar at 37.5 C., yellowish discs being formed. 

 Material from the centre of the " favus cup " or the ground- 

 up cup may be used to plant in liquid agar, plates being then 

 poured (Plant). 



Tinea versicolor (chromophytosis y pityriasis versicolor) is 

 caused by the microsporon furfur. 



History. Microsporon furfur as the cause of this skin dis- 

 ease was discovered by Eichstedt in 1846. 



Morphology. It resembles the tricophyton, but the spores 

 have a tendency to aggregate in masses, and the hyphse are 

 generally bent at right angles. It can be demonstrated by 

 putting some of the fine scales in liquor potassse and examin- 

 ing or may be stained with the ordinary dyes. 



Biologic Character. It grows especially well on potato, 

 developing in four or five days white or yellowish-white 

 colonies. 



Pathogenesis. In man it causes an infection of the skin, 

 of the trunk principally, characterized by macular yellowish 

 furfuraceous patches. 



