168 



INFECTIONS CAUSED BY MOLDS 



very numerous large, multicellular, spindle-shaped, rough, and thick- 

 walled macroconidia are also borne on the hyphae. The macro- 

 conidia of M. Audouini are' smaller, have fewer cells, and appear to 

 be depauperate forms of the type. These macroconidia are so dif- 

 ferent from the clavate macroconidia of Trichophyton with smooth, 

 thin walls, rounded tips, and few cells, that there is usually little 

 difficulty in deciding which type is under observation. 



A number of species of Microsporum have been described. Castel- 

 lani recognized sixteen, of which four were of human origin, the 

 remainder of animal origin. The important species are M. Audouini, 

 seen only in man; M. Canis {M. lanosum, M. Felineum), and M. 

 gypseum, from animal sources. Most of the other described species 

 are only varieties of the first two named. These two species may be 

 differentiated by the characters tabulated below (adapted from Plant 

 and Griitz). 



Microsporum Audouini 



Highly contagious, causing school 

 epidemics. 



Of long duration, resistant to treat- 

 ment. 



Only the head usually involved, ex- 

 ceptionally areas in the immediate 

 vicinity. 



Inflammatory reactions mostly lack- 

 ing if vmtreated. 



Cultures grow slowly. 



Colonies remain grey or white with 

 a reddish color visible in reverse of 

 culture. 



Only rarely transmissible to animals 

 from cultures. 



Microsporum Canis 

 Less contagious, may cause family 



epidemics. 

 Of shorter duration, about 1 year. 



Frequently also skin lesions at a dis- 

 tance from the head. 



Inflammatory reactions often present 

 without any irritation from treat- 

 ment. 



Cultures grow more rapidly and colo- 

 nies attain a larger size. 



Colonies become tobacco brown to 

 reddish in center. 



Rabbits and guinea pigs easily in- 

 fected from cultures. 



Further differentiation may be made on the basis of colony struc- 

 ture. In M. Audouini there is often a small central knob elevated 

 above the surface of the colony. In some strains the latter is marked 

 radially by four to six deep clefts. The whole surface has a velvety 

 texture. In M. Canis there is a central flat area surrounded by an 

 elevated zone of aerial mycelium with usually no folding. The 

 surface has a woolly texture. 



Endothrix Species of Trichophyton. The pure endothrix species 

 of Trichophyton are from human sources. Their infections occur 

 mainly in the scalp, the majority of the cases of ringworm of the 



