THE TR1CHOPHYTONEAE 383 



cause favus, whereas it is known that this disease may be caused 

 by some species of Trichophytum (Trichophyton) and Micro- 

 sporum (Microsporon) as well. Again Microsporum is under- 

 stood to include those species which produce a sheath of closely 

 aggregated tiny spores, never in chains, around the basal part of 

 the hair. In Trichophyton, on the other hand, the infecting 

 hyphae are intrapilar and become closely segmented, appearing 

 as chains of spores. The spores, however, arise in chains from a 

 circumpilar sheath. In some species the circumpilar portion dis- 

 appears; these were regarded by Sabouraud as "endothrix." In 

 others the circumpilar sheath is the most prominent feature; 

 hence these species are termed "ectothrix." The transition group 

 between these two constitute Sabouraud's "neoendothrix" species. 



Species of Epidermophyton and Endodermophyton are under- 

 stood to be limited to the glabrous skin. The only kind of spores 

 formed in culture by Epidermophyton are separate fuseaux; by 

 Endodermophyton, arthrospores. 



Several systems of classification have been proposed, including 

 those by Sabouraud (1910) and its modifications (1929), by Ota 

 and Langeron (1923), by Langeron (1926), by Grigoraki (1925, 

 1929), by Langeron and Milochevitch (1930), and by Dodge 

 (1935). The system of Sabouraud is fundamental and is in general 

 usage among students of this group, since it has the merit of being 

 workable. A comparison of his larger groupings with those em- 

 ployed by Dodge is shown in Table 28. 



Emmons (1934) found by a study of representative members of 

 this group that botanical characteristics exist as means for classify- 

 ing them and that such characteristics should replace clinical ones. 

 He employed shape, size, and method of formation of conidia to 

 separate Trichophyton, Microsporum, and Epidermophyton. 

 Trichophyton possesses clavate conidia that are thin-walled and 

 have few septations; Epidermophyton, conidia that are clavate to 

 ovate and are thick- walled with few septations; and Microsporum, 

 conidia that are spindle-shaped, thick-walled, and frequently sep- 

 tate. Emmons regarded spirals, chlamydospores, and nodular 

 organs as of little value in classification. 



In separating species Dodge (1935) based his key largely on cul- 

 tural characteristics of giant colonies. This means of identifica- 

 tion becomes increasingly useful as the student gains experience 



