It is the tendency to perniciousness which makes us dread malignant tertian as we can never be sure that a paroxysm may not develop cerebral or algid manifestations and these show a very high death rate, 25 to 50%, even when promptly treated. As regards relapses quartan is the malarial fever which is most apt to show this feature and aestivo-autumnal the least. Deaderick gives the percentage of cases showing relapses in quartan, benign tertian and aestivo-autumnal as 65, 55 and 45. The great importance of malaria is rather its invaliding tendency and by thus reducing the powers of resistance it makes the death rate from intercurrent diseases higher. Tropical malaria does not seem to affect the native as it does the European but the high death rate of infants among the natives is undoubtedly largely connected with this disease. Statistics vary greatly as to the percentage of fatal cases in malaria. Certain figures from tropical countries give fatal results as occurring in from 2 to 10% of cases, while statistics from temperate climates show a death rate below 1%. The mortality from pernicious types of malaria is about 25%. PROPHYLAXIS AND TREATMENT =Prophylaxis.=—There are three methods in the prevention of malaria, all of which may be combined, as was the case in the Canal Zone region of Panama. These are: (1) Destruction of anopheline mosquitoes; (2) protection of the individual from the bites of mosquitoes, and (3) quinine prophylaxis. It may be stated that it is frequently advisable to carry on the mosquito warfare without regard to the question of the kind of mosquitoes destroyed. In general terms the malarial mosquito breeds in the suburbs of towns or in districts more distinctly rural, while the transmitter of the more dreaded yellow fever, prefers breeding places in the immediate vicinity of city houses. Bentley has recently noted that, with improvement in agricultural methods and utilization of marshy lands, malaria tends to disappear as much from the physical improvement and thereby greater resistance of the people as from the destruction of mosquitoes by the draining of the swamps. The resulting greater prosperity makes better food and shelter obtainable. 1. _Destruction of Mosquitoes._ Such measures may be directed either toward the larva or fully developed insect. (_a_) Measures against larvae. When practicable permanent measures should be preferred to temporary ones and when agricultural development goes along with drainage of swamps the cost is repaid.