1) the a. reviews the routes of natural transmission of rat leprosy and the experimentally induced disease. 2) the infection in the natural disease must be made by contact with an infected rat or through the gastro-intestinal route by eating infected tissue. 3) they were found acid-fast bacilli in lice (polyplax spinulosa) caught on rats dying of leprosy; but it was impossible to obtain cultures in l？wenstein medium, from these lice. 4) rat leprosy emulsion introduced into the stomach, may infect rats. five rats fed with infected material became infected. 5) after subcutaneous or intraperitoneal inoculation there were obtained infection in almost 100% of cases. 6) it was possible to infect didelphis aurita after inoculation of infected rat material. these animals most likely are more susceptible to rat leprosy than to human leprosy. 7) it was possible to infect chicks by inoculation in chest muscle, by intraperitoneal injection and by gastrointestinal route. 8) it was possible to infect pigeon by inoculation in chest muscle and by intravenous inoculation.