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256 three or four days of the disease. Yet another point these experimenters sought to establish, viz. that this phase of the yellow -fever germ is so minute that it can pass through a Berkefeld filter. Further, that blood from a yellow -fever infection produced by injection of filtered serum will, on being injected into another non-immune, again confer the disease; proving that the virus so conveyed was capable of multiplying— that is to say, that it is not a toxin or chemical body merely, but that it is a living germ. These latter inferences are deduced from what was practically only one experiment. Although the evidence, therefore, is somewhat meagre, yet, considering the high order of the other work accomplished in the same field by these American and subsequent observers, we are almost justified in concluding with them that, like the germ of rinderpest, of horse-sickness, and of foot-and-mouth disease, at least one phase of the yellow-fever germ as it exists in the blood, though particulate, is ultramicroscopic. The mosquito the intermediary and diffusing agent of the germ of yellow fever.— Having satisfied themselves by direct observations, and by a long series of carefully conducted culture experiments on the blood, that the germ of yellow fever was not of an ordinary bacterial nature, guided by the epidemiological considerations detailed above, and encouraged by the recent discoveries in the etiology of malaria, the American observers thought that possibly, as in malaria, the mosquito was an essential factor in the life cycle of the yellow-fever germ, as Finlay had conjectured many years before. After some preliminary experiments, which unfortunately proved fatal to Dr. Lazear, one of the original members of this courageous band of observers, carefully planned systematic attempts were made to convey yellow fever by means of the bite of the common West Indian mosquito, Stegomyia calopus (S. fasciata). Twelve non-immunes, who had had no opportunity of contracting the disease from other sources, were bitten by mosquitoes previously fed on yellow-fever patients. Of the men so bitten, ten (83.3 per cent.)