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284 habitat, or because it is not usually found in the peripheral blood.*

Edington claims to have shown that when cattle, natives of the South African endemic regions of Texas fever, are inoculated with rinderpest, they develop hæmoglobinuria and the other symptoms of Texas fever, from which disease they might be supposed to be pathologically immune. The blood of immune cattle in Texas fever regions, we know, contains, in small numbers, the babesia. Edington's experiments show that the supervention of a second infection, rinderpest, determines the multiplication of the latent babesia, and the explosion of the characteristic symptoms. May this not be in strict analogy with what happens in blackwater fever? The infection of blackwater fever may remain latent for considerable periods, until provoked into activity by some special agency, as cold, shock, quinine, or some additional infection, especially malaria. Cook has placed on record five cases of blackwater fever in which an attack of spirillum fever appeared to be the provocative agent. Manifestly, the etiology of blackwater fever is not yet settled, and it is wise to preserve an open mind on this important subject.

Incubation period.— We know nothing definite as to the incubation period of blackwater fever. Scott, in British Central Africa, noticed that the attack usually occurred about eight days after exposure in certain low-lying districts. That the disease may remain in abeyance for a considerable time is proved by the facts that recurrences after long intervals months are very common, in fact the rule; and that in some cases the first attack may manifest itself in Europe several months after the patient has left the endemic regions. I have recently