160 INFECTIONS CAUSED BY MOLDS 



nucleate. Mitotic division of the nuclei was not observed. Mito- 

 chondria and metachromatic granules were also demonstrated. Em- 

 mons confirmed the nuclear findings. 



Enzymes. The biochemical activities of the skin fungi have been 

 investigated by Tate ^^ who found that all the species which he in- 

 vestigated were proteolytic and secreted lipase, urease, maltase, and 

 diastase. None contained invertase, inulase, lactase, or zymase. 

 The proteolytic enzyme resembled trypsin, acting in an alkaline 

 medium; it did not digest coagulated egg. None of the strains studied 

 could hydrolyze keratin. The fat-splitting activities of ringworm 

 fungi was studied by Mallinckrodt-Haupt, who found that the species 

 studied could grow in mineral solutions with neutral fats as the sole 

 source of carbon, if these were of animal origin, but showed little or 

 no growth with vegetable oils. 



Main Groups of Dermatophytes. Sabouraud recognized four main 

 groups of dermatophytes, Microsporum, Trichophyton, Epidermo- 

 phyton, and Achorion. These were defined on the basis of the clinical 

 type of lesion produced and the microscopic appearance of the fungus 

 in the lesion, specifically, its relationship to invaded hairs. Thus 

 Microsporum produced on the surface of a parasitized hair a mosaic 

 pattern of small spores, Trichophyton was characterized by a linear 

 arrangement of spores on the hair surface, Epidermophyton did not 

 attack the hair, and Achorion produced peculiar yellow crusts and 

 scutula on the scalp. The first three groups stand as valid genera 

 if defined according to mycological criteria, although a considerable 

 revision of Epidermophyton is required because of its use by some 

 dermatologists for any fungus found growing on the glabrous skin, 

 whether or not it was capable of invading the hair. The fourth genus, 

 Achorion, cannot be defined as a genus of fungi by any valid method, 

 and its species should be distributed to appropriate genera, as we 

 shall see in a later paragraph. 



Sabouraud divided the genus Trichophyton into subgenera on the 

 basis of the position of the fungus with regard to the hairs: Endothrix 

 species of Trichophyton growing entirely within the hairs; Ectothrix 

 species of Trichophyton growing mainly on the surface of hairs ; and 

 Ectoendothrix or Neoendothrix species occupying an intermediate 

 position between the two other groups. 



The key to the main groups of dermatophytes presented below is 

 based in part on Sabouraud's clinical classification and in part on 

 mycological criteria.*' The main groups write their own label, so to 

 speak, on the invaded hair, and their identification is often easier 



