The dermatophyte Trichophyton mentagrophytes has been known for a long time to be an etiologic agent of tinea in man and animals. It is commonly found in ringworm infections of man and a great variety of domestic and captive animals such as horses,1 chinchillas,2 dogs,3 cats,4 calves,5 and monkeys,6 as well as many wild animals such as foxes,7 muskrats,8 squirrels,9 etc. The occurrence of T. mentagrophytes infections among the rodents commonly used as laboratory animals (mice, guinea pigs, rabbits, and rats) has been reported by many workers in different parts of the world. Parrish10 published an account of an epi zootic in England in which nearly 50% of a population of 2500 mice were infected with T. mentagrophytes. The disease spread to some laboratory attendants. Mackinnon,11 in Uruguay, found 70 cases of ringworm due to