Mosquitoes, bed-bugs, head lice and scabies mites were collected from the dwellings of persons suffering from lepromatous leprosy (patient collections) and from those where no known case of leprosy existed (random collections). Suspensions made from pools of these arthropods were used for making smears for acid-fast staining, culture on Lowenstein-Jensen medium and for mouse footpad inoculation. In the patient collections acid-fast bacteria were detected microscopically in 4. 1 % of Anopheles. 3.6% of Culex, 22.2% of A nopheles and Culex (mixed), 4.8% of Cimex, 7.4% of Pe diculus and in a single pool of Sarcoptes. In the random collections acid-fast bacteria were found in 7.7% of Anopheles, 6.8% of Culex, 9.2% of Cimex, in none of Pediculus, and in 2 out of 3 Sa rcoptes pools. Footpad multiplication was obtained from 2 Culex pools, one collected at random and the other from patients. The findings strongly support the conclusion that the acid-fast bacteria obtained from the two pools of Culex were indeed My co. leprae.

Laboratory-reared Culex fa tigans and Cimex hemipterus were fed on untreated lepromatous leprosy patients. The presence of acid-fast bacteria in a high proportion of these insects after feeding showed that they can take up the bacilli from the patients' blood. The dependence of infestation of fed insects on the degree of bacteraemia in patients and the detection in Cimex of bacteria-laden leucocytes suggest that the insects took up the bacilli along with the blood rather than fr om the skin. Results of mouse footpad harvests showed multiplication of My co. leprae, and therefore one must conclude that the leprosy bacilli in the insects were vi able.