RESUMO
1. The reasons which induced us to take up the study of rat leprosy are as folllows: a. The very close association between this disease and human leprosy. b. Human leprosy cannot be conveyed to lower animals, whereas almost 100 per cent of successes can be assured by inoculating rats with B. Leprae murium provided the appropriated technique is used. c. The course of the disease in the rat is a relatively rapid one. 2. As will be observed from the title, we discovered that structures resembling tumor growths occurred in the abdominal cavity following on the intra-abdominal inoculation of rat leprosy. Such growths, there is reason to believe, are granulomatous and are due to multiplication of the peritoneal endothelial cells and phagocysosis of bacilli together with multiplication of bacilli inside cells. We have also remarked on the fibrosis, caseation and liquefaction which ocur in the tumours. 3. We think taht a description of the mode of origin of these grwths may help to shed some light on the pathology of human leprosy and also, possibly, on the origin of other new growths more obscure in etiology.