Conant, 1 in 1936, found that the use of polished rice medium assisted in the differentiation of Microsporum audouini from Microsproum canis. The former failed to grow abundantly on rice, producing only a progressive discoloration of the grains, while the latter grew luxuriantly. In 1943, Benedek 2 discovered that the presence of a certain bacterium on rice medium stimulated not only the growth of M. audouini but also the development of macroconidia characteristic of the genus Microsporum. The bacterium was studied, described and classified by the author as Bacillus weidmaniensis. In 1947, Hazen 3 found that the effects obtained by Benedek could be reproduced when M. audouini was grown on honey agar enriched by yeast. She expressed the opinion that M. audouini is deficient in certain factors which apparently are supplied by yeast extract. This opinion was also expressed by Benham. 4 Luxuriant cultural growth on rice and formation