SUMMARY: The optimum temperature for the growth and sporulation of Trichophyton ~U S~C O Z O T was 25-30' ; 4 0 ' inhibited growth. A range of pH values from 4 to 10 was compatible with growth, the optimum pH value being slightly less than pH 7. Macroconidia were produced over a narrower range and were most abundant at pH 8.Percentage germination and length of germ tube were greatest at 100 yo humidity. No germination occurred at humidities of below about 95 yo. Exposure to light had no effect on growth rate, sporulation or pigmentation.The carbon compounds which supported best growth were mannose, glucose, mannitol and maltose. Nitrates were not utilized, and ammonium sulphate, urea and asparagin supported poor growth. The amino-acids leucine, glycine, histidine and cysteine were utilized; with all other single amino-acids tested, growth was negligible. Methionine and phenylalanine were inhibitory.T . persicolor was autotrophic for vitamins. It grew as well on a vitamin-free medium as on the basal medium.The elements zinc, iron, copper and manganese, as sulphates, stimulated the growth and sporulation of T . persicolor on a medium treated for the removal of trace elements.This investigation arose from an observation that two isolates of Trichophyton persicolor (M2, isolated in France, and M3, isolated in Britain) grew yery differently from each other on Sabouraud's ' conservation ' medium in which a peptic digest of meat replaced commercial peptone, while on Sabouraud's maltose ' proof' medium containing the same digest as nitrogen source their cultural appearance was similar. As no detailed investigation of the physiology of T . persicolor had been made previously it was decided to make a study of the nutritional and physico-chemical growth requirements of M2 and Ma. Other isolates of T . persicolor were frequently included for comparison. Among these were one (M 323) from Dr R. Vanbreuseghem (Institut de Mddecine Tropicale Prince-Ldopold, Anvers), four (M 330, M332, Ma38 and M335) from Dr Jacqueline Walker (London School of Hygiene and Tropical Medicine) and two (S45 and S78) recently isolated from material sent to this laboratory.No explanation of the difference between M2 and M 3 has emerged during the course of this work, but an outstanding effect of environmental conditions of the production of macroconidia has been frequently noted.
