Every dwelling in Colon and Panama was thoroughly fumigated with pyrethrum powder or with sulphur, and then cleared of dust and refuse, which, with the insensible but not always dead mosquitoes, was then burnt. The complete, and, it is hoped, final freedom from yellow fever in Colon and Panama has been obtained by means of a proper water supply and universal paving with brick or cement, as well as the supply of proper drainage. Formerly water for domestic use was stored in cisterns, tanks, tubs, jars, and so forth, and, after rain, water stood stagnantly in a thousand ruts and holes in the unpaved squares, streets, and lanes. These breeding-places of the _stegomyia_ have now been done away with completely in Panama, and almost completely in Colon. The latter city is so low-lying and flat, and subject to such heavy rainfall, that pools of stagnant water will form. They can, however, be oiled, which kills the larvæ, and, moreover, it is Panama, and not the wind-swept, salt-saturated, town of Colon, which has been the chief source of yellow fever. The last case of the disease in Panama occurred in November, 1905, and in May, 1906, there was an isolated case in Colon. The infection is considered to be at an end in a city three months after the last case, that being the lifetime of _stegomyia_. After this period, all infected _stegomyia_ having died, those that remain are powerless for harm. Nevertheless, the stringent measures for their destruction are not relaxed, as, while _stegomyia_ exists, the germ, if re-introduced, will be rapidly disseminated. Thus the yellow fever, having taken toll for four hundred years of those who crossed the Isthmus, has been completely eradicated by. Colonel Gorgas and his assistants. It is a triumph of science and of despotic government combined; and only in this combination can preventive medicine achieve full success. There is one other aspect of the yellow fever campaign which must be mentioned before going on to describe the fight with malaria.