166 INFECTIONS CAUSED BY MOLDS 



by direct contact, more frequently from the walls of stalls and litter 

 about barns. Children are frequently infected from cats and dogs 

 with which they play. The fungus has been isolated from the litter 

 of animal stalls ; this shows that the fungus is capable of living sapro- 

 phytically upon vegetable matter, as many of the other pathogenic 

 fungi are. The spores can probably remain viable for long periods 

 outside the animal body. 



The disease may attack all parts of the skin surface. Clinically 

 a division is made between ringworm of the hairy parts and ring- 

 worm of the smooth skin ; ringworm of the nails also occurs and may 

 constitute a reservoir of infection which is difficult to eradicate. The 

 nature of the infection varies considerably according to the degree 

 of inflammatory reaction of the invaded tissues. .Thus a wide variety 

 of clinical types may be recognized, but the differences are more ap- 

 parent than real because fundamentally the pathologic changes are 

 the same in all the types. 



The infection begins in a hair follicle, from which focus it extends 

 to the surrounding skin and into the hair. In the skin, in addition 

 to redness due to congestion, there occurs scaling caused by an over- 

 production of epithelium in response to the irritation caused by the 

 presence of the fungus, an exudation of fluid, and an accumulation 

 of leucocytes. A very characteristic feature is the formation of con- 

 centric rings of inflammatory reaction. This is, of course, more 

 apparent on the smooth skin. The formation of these rings has not 

 been satisfactorily explained, but may be due to the same mechanism 

 which leads to the formation of concentric rings of growth so fre- 

 quently seen when molds are grown in Petri plate cultures. The 

 infection tends to spread at the periphery and heal in the center. 

 It is the formation of these advancing rings of inflammatory reaction 

 which has given origin to the popular name ringworm (Latin, tinea; 

 French, teigne). 



Microsporum Ringworm. In Microsporum infection, although the 

 mycelium invades and is found inside the hairs, the spores are formed 

 on the exterior. There is some difference of opinion as to whether 

 these spores are to be considered arthrospores, i.e., produced by frag- 

 mentation of the mycelium, or whether they are conidia. But they 

 occur in irregular clusters not in chains, and are closely packed to- 

 gether on the surface, forming a sort of mosaic. The individual cells 

 are polyhedral in form, not rounded or cylindrical. In Trichophyton 

 infection, for comparison, the mycelium may be within or without 

 the hair, or both, and the spores are formed in both places, but they 



