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Details of bacterial cell structure have been elucidated to some extent through electron microscopy of ultrathin sections. Less has been reported on the application of this relatively new technique to the problem of fungal architecture (1-4) and virtually nothing has been published on thin section studies of dermatophytes, so well recognized clinically as the causative agents in numerous human cutaneous infections. This paper describes exploratory experiments on thin section electronmicroscopy of Epidermophyton floccosum. METHODS Approximately 1 mm. cubes were cut from the periphery of 14 day colonies of E. floccosum grown on solid Sabouraud's medium at room temperature. Some of these were fixed in buffered 1% osmium tetroxide (5) and others in buffered 0.6% potassium permanganate. Still others were fixed in buffered 1 % chromate, 1 % lead acetate, and 1.5% phosphotungstate. Specimens after fixation for 2-16 hours were dehydrated through the usual alcohol series and embedded in n-butyl methacrylate. Sectioning was performed on a Porter-Blum microtome with glass knives (6). The sections were mounted on carbon films and examined in an RCA EMU microscope fitted with a 25 or 50 ju objective aperture.

As is well known, three genera of Dermatophytes are recognized on the basis of microscopic morphology in culture; namely, Trichophyton, Microsporum and Epidermophyton. Differentiation of species is not a great problem in the last two genera since they are few in number and sufficiently characteristic to make identification relatively simple. In the genus Trichophyton, however, a different situation exists. A large number of species has been described for this genus since the time of the original description of Trichophyton ton-surans by Malmsten in 1845 (1). At the time Sabouraud published “Les Teignes” in 1910 (2), he listed 31 species in the genus Trichophyton, basing species differentiation on the morphology of the fungus colony on a peptone-carbohydrate medium, his so-called “Milieux d'epreuve.” From time to time it has been shown that many of these were not distinct species, but merely variants or mutations of one or another of the well-recognized types. There is still some disagreement among both European and American mycologists as to the number of species they recognize, and also which ones should be regarded as variants and which should fall into synonymy.

A review of the literature on human experimental dermatophyte infections is presented. The aspects discussed include the various types and quantity of fungus applied, the sites of inoculation, the physical state of the stratum corneum, the influence of steroids and anti-fungal agents and resistance to reinfection. New methods allow one to produce a standard reproducible infection on human skin with a quantitated inoculum.

Studies of the nutritional requirements of dermatophytes have been made by various workers using stationary cultures on solid and liquid media. Conclusions as to the ability of these fungi to grow on inorganic nitrogen in the presence of a suitable carbohydrate source are contradictory. Various sporulating strains of Trichophyton and Microsporon have been found to grow under these conditions. (Bocobo and Benham (3), George (4, 5), Giblett and Henry (6), Silva and Benham (19), and Bereston (2)). However, only pleomorphic strains of T. menta-grophytes grew on inorganic nitrogen, while granular sporulating strains did not according to others (Mosher et al. 1936 (13), Robbins and Ma (18), Nickerson (14), McVeigh and Campbell (11), and Stockdale (20)). Technical considerations such as criteria for evaluating growth, the use of media only partly defined chemically, and variations in the size of inocula may be responsible for some of these discrepancies.

The sterols of filamentous fungi have been rather poorly investigated (1-3) although the first fungal sterol, ergosterol, was isolated by Tanret (4) as early as 1889. In contrast, the sterols of the unicellular fungi, the yeasts, have attracted much more attention (2,3,5-17). Petroleum ether extracts of 14 species of the dermatophytes (genera Epidermophyton, Microsporum, Trichophyton), representing one group of closely related filamentous fungi, were, therefore, examined for the presence of free sterols in continuation of our investigations on the chemical constituents of pathogenic fungi.

In a survey to isolate dermatophytes from clinical specimens, Taplin's dermatophyte test medium and two commercial DTM products were compared with Sabouraud's dextrose agar containing cycloheximide and chloramphenicol. Though statistical differences and similarities were detected among the media under actual clinical conditions, the differences themselves could not be attributed to the medium, size of inoculum or other specific sources of variation because of unknown factors inherent in this approach. Therefore, a controlled quantitative test was made to compare DTM with commonly available mycological media using quantitated spore preparations of Trichophyton mentagrophytes. All media tested equally supported the growth of the dermatophyte as indicated by the statistical similarity among colony counts. Quantitation of number of spores produced did not differ among Taplin's DTM, Difco DTM, Pfizer DTM, and Sabouraud's plus antibiotics. Significantly fewer spores were produced on Littman's oxgall agar and significantly more on ink blue agar.

Improved embedding medium, variations in fixation, and specific stains enable one to demonstrate hitherto non-detectable details (1). It is in order, therefore, to review the fine structure of E. floccosum.

The study of the experimental inoculation of dermatophytes in man has been largely neglected. However, in the course of the investigation of an epidemic of body-ringworm in Malaya (Sanderson and Sloper, 1), certain preliminary studies were made of the natural course of artificially-induced infections due to Trichophyton mentagrophytes (Robin, Blanchard, 2), Epidermophyton floccoswn (Harz, Langeron and Milochevich), and Trichophyton rubrum (Castellani, Ota). These are reported first because of the paucity of comparable observations, and second, because of their therapeutic implications. For it will be shown that lesions due to all three organisms healed spontaneously, a result fairly well-recognized in the case of the zoophilic Trichophyton mentagrophytes, but entirely unexpected in the case of Trichophyton rubrum and the typically anthropophilic Epidermophyton floccosum.

Of the three genera of dermatophytes, the genus Epidermophyton has caused the least difficulty in the problem of identification. This is due no doubt to the fact that there is at present but one recognized species, and that the generic characteristics are so outstanding. Epidermophyton floccosum is described as a parasite of the smooth skin and nails of humans and does not invade the hair.

Recently the anthelmintic compound 2(4'thia-zolyl)-benzimidazole (thiabendazole-Merck Sharp and Dohme) was reported to be active against some pathogenic fungi (1). In our laboratory we have confirmed the original report, and also tested thiabendazole against additional fungi.