RINGWORM. 115 



mosaic and not in chains (fig. 20). It does not invade 

 the interior of the hair, but forms a sheath of spores and 

 mycelium outside the submerged portion of the hair ; 

 this sheath projects for a short distance above the sur- 

 face of the scalp and may be seen with the naked eye. 



This fungus usually attacks the scalp in children. 

 It is very rare in adults, and it rarely attacks other 

 regions than the head. It is thought by some to be 

 always caught from a human case of the disease, but 

 there are reasons for thinking that it may be derived by 

 infection from the horse or cat. 



FIG. 21. Trichophyton endothrix. 



The most important clinical fact about the micro- 

 sporon Audouini is that ringworm caused by it is 

 extremely intractable and may run a prolonged course 

 in spite of the most skilful treatment. 



The trichophyton endothrix attacks the interior of the 

 hairs, and forms long chains. Its spores are somewhat 

 larger than those of the preceding species, but the 

 difference is not great ; the organism is most easily 

 recognised by the chain-like arrangement of its spores, 



I 2 



