=Prophylaxis.=—As was noted under epidemiology there seems to be little evidence to show that insects play any part in the transmission of leprosy. Nevertheless it would seem advisable to prevent flies from becoming contaminated with the discharges from leprous ulcerations which so often teem with leprosy bacilli. This possible method of transmission would seem more deserving of attention than the question of the taking up of bacilli from the blood by mosquitoes, bedbugs or biting flies, as the leprosy bacilli are found in the blood of nodular leprosy chiefly during the febrile accessions and very rarely in the blood of cases of nerve leprosy. In all of the ordinary insects the bacilli seem to disappear in a very short time, with the exception of the cockroach, for which reason it would seem advisable to destroy these pests, which can be easily done by sprinkling around a little sodium fluoride. There is some evidence that scabies favours infection so that this disease should be looked for and actively treated in endemic areas. Leprosy tends to spread where there is marked personal uncleanliness and close contact with lepers in overcrowded quarters. Many authorities consider the free use of soap and water the most important means of avoiding infection. While segregation is generally considered the one proven prophylactic measure there are those who question its value. There does not seem to have been any very marked influence on the spread of leprosy among the native Hawaiians through the enforcement of isolation of such cases. Partial segregation at their homes has given very satisfactory results. Where a leper is not excreting bacilli, or where acid-fast organisms cannot be found after careful search there is no danger. Such patients, however, should report for examination every few months. Evidence as to contact indicates that all young children are particularly liable to the infection, as has been noted for children of lepers and brothers and sisters. Even if segregation of lepers is not carried out as regards adults, it should be the rule for children, so that infants and young children should be separated from their leper parents or parent. A very remarkable feature in connection with leprosy is the hysterical dread that many communities have of a leper, when they must know or could easily learn, that the contagiousness of the affection is so slight, that notwithstanding our efforts, we can scarcely point to a single instance to prove undoubted transmission of the disease from one person to another. At any rate knowing that immense numbers of the bacilli are given off from ulcerations and the nose, we should guard against the dissemination of leprosy bacilli from such sources.