Methods of control of the disease must look to the prevention of infection of the flies, and to their avoidance and destruction. Along the first line, much was hoped from temporary segregation of the sick in regions where the fly was not found. On the assumption that the flies acted as carriers only during the first two or three days, it was supposed that even the "fly belts" would become safe within a few days after the sick were removed. The problem was found to be a much more difficult one when it was learned that after a given brief period the fly again became infective and remained so for an indeterminate period. Nevertheless, isolation of the sick is one of the most important measures in preventing the spread of the disease into new districts. Much, too, is being accomplished by moving native villages from the fly belts. (c.f. fig. 137.) All measures to avoid the flies should be adopted. This means locating and avoiding the fly belts as far as possible, careful screening of houses, and protection of the body against bites. Clearing the jungle along the water courses for some yards beyond the natural range of the fly has proved a very important measure. Castellani recommends that the area be one hundred yards and around a village three hundred yards at least. Detailed studies of the parasites and the natural enemies of the tsetse-fly are being undertaken and may ultimately yield valuable results. SOUTH AMERICAN TRYPANOSOMIASIS--The tsetse-flies are distinctively African in distribution and until recently there were no trypanosomes known to infest man in America. In 1909 Dr. Chagas, of Rio de Janeiro described a new species, _Trypanosoma cruzi_, pathogenic to man. _Trypanosoma cruzi_ is the causative organism of a disease common in some regions of Brazil, where it is known as "opilacao." It is especially to be met with in children and is characterized by extreme anemia, wasting, and stunted development associated with fever, and enlargement of the thyroid glands. The disease is transmitted by the bites of several species of assassin-bugs, or Reduviidæ, notably by _Conorhinus megistus_. The evolution of the parasite within the bug has been studied especially by Chagas and by Brumpt. From the latter's text we take the following summary. The adult trypanosomes, ingested by a _Conorhinus megistus_, of any stage, first change into Crithidia-like forms and then those which remain in the stomach become ovoid and non-motile. Brumpt found these forms in immense numbers, in a _Conorhinus_ which had been infested fourteen months before. The forms which pass into the intestine quickly assume the _Crithidia_ form and continue to develop rapidly under this form. Some weeks later they evolve into the trypanosome forms, pathogenic for man. They then pass out with the excrement of the bug and infect the vertebrate host as soon as they come in contact with any mucous layer (buccal, ocular or rectal). More rarely they enter through the epidermis.