TRICHOPHYTONEAE 



447 



but as it penetrates deeper, it remains unstained with the usual dyes. The 

 hyphae gradually fill the hair and render it very fragile so that it breaks at 

 the neck of the bulb. 



In the neoendothrix type, the conditions found in the early stages persist 

 a long time, about one quarter of the hairs at a given time showing hyphae 

 on the outside of the hair or between the hair and the wall of the follicle. 

 This persistence of the early stage of infection occurs in those species which 

 normally infect domestic animals and only occasionally are found in man. 



Fig. 77. — Section tlirough hair from case of tinea tonsurans. 1, caused by species of Trichophy- 

 ton; S, caused by Ectotrichophyton. (After Sabouraud.) 



Similarly in the Neomicrosporum group, the external hyphae which form the 

 spore sheath in the early stages persist much longer than in the Eumicrosporum 

 group, which includes M. Audouini. 



In the ectothrix group there are so many variations in the different 

 species in respect to the form and dimensions of the cells, the regularity of 

 the arrangement, and the proportion of the hyphae outside the hair, that gen- 

 eralization is difficult. In Ectotrichophyton and Favotrichophyton (the mi- 

 croide group), all the species are pyogenic, all invade the hair as slender 



