TRICHOPHYTONEAE 467 



found that Microsporum Audouini and Epidermopliyton floccosum {E. inguin- 

 ale) have an optimum hydrogen ion concentration of 6.5 to 7.2, while Achorion 

 and Megatrichophyton roseum {Trichophyton rosaceum), Favotrichophyton 

 violaceum (T. violacenm) , and Ectotrichophyton mentagrophytes have a much 

 wider range. That author used this fact to explain that the former species 

 are practically confined to prepubertal individuals in which the hairy areas 

 have a pH of 6.2-6.5, and disappear after ])uberty, when the pH of these areas 

 has increased to 4 :5-5.6. 



Scolari (1931), working with Achorion Schoeyileini, Microsporum Audouini, 

 and Favotrichophyton violaceum, found differences in growth rates on media 

 of different pH, but found practically^ no alterations in colonies nor in spore 

 forms, other than the disappearance of spores near the limits of growth. 



Further work on temperature has developed partly in connection with 

 observations in laboratory cultures where it lias been noted that the color at 

 37° C. may be altogether different, although equally characteristic, from that 

 at room temperature (about 20° C). In the systematic discus.sion in this work, 

 colors are to be assumed at the room temperature common at the place cul- 

 tivated unless otherwise specified. This temperature may be as low as 15° C. 

 in many of the European laboratories, about 20° C. in American, and somewhat 

 higher in the tropical ones (about 25-30° C). Skin temperature is usually 

 somewhat less than body temperature, a fact frequently overlooked in dealing 

 with skin parasites (Kadisch 1933). This is especially true for the group under 

 consideration, which does not penetrate beyond the horny layer. Therefore, 

 while room temperature is undoubtedly too low to reproduce conditions under 

 which W\ey grow on the host, 37° C. is several degrees too high. For example, 

 Jadassohn & Stahelin (1930) have showai that when inoculated guinea pigs 

 are kept in a ventilated incubator at 36-39° C. and show a rectal temperature 

 of 39-41°, about double the time was necessary to develop lesions in the case 

 of Ectotrichophyton mentagrophytes {T. gypseum) and Achorion muris (A. 

 Quinckeanum) . 



Similarly Kadisch (1933) has shown that guinea pigs inoculated with 

 Achorion gypseum at Davos, Switzerland, 1,600 m. where the air tempera- 

 ture was lower and the oxygen pressure less than the controls, inoculated in 

 Berlin, developed superficial lesions much more slowly, and the lesions healed 

 much more rapidly than the controls. In vitro experiments also pointed to 

 an optimum temperature for this organism intermediate between room tem- 

 perature and 37° C, and showed that any reduction of oxygen pressure near 

 the optimum temperature greatly checked growth. Folding of colonies is 

 greater near the optimum temperature and is taken as a need for exposure 

 of a larger area to the air during- rapid growth. Perhaps these facts explain 

 why most of the ringworm infections occur at lower elevations and in the 

 warmer regions of the earth. 



In most cases it appears to make little difference whether the colony de- 

 velops in light or darkness. Peiia Chavarria & Clark (1924) found the follow- 

 ing durations of exposure to ultraviolet light at 30 cm. from the arc necessary 



