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XIII] the latter become infective to man fourteen days after the hatching.

The parallelism between the etiology of yellow fever and that of malaria is very complete, and encourages ' the conjecture that the germ, like that of malaria, is of a protozoal nature; that as a result of a sexual process it undergoes growth and development in the mosquito; and that the sporozoites resulting from this process are emitted in the salivary secretion of the infected mosquito when, at any time subsequent to the completion of the developmental process, she proceeds to feed on blood. Although the germ of yellow fever as it occurs in the blood may be ultramicroscopic, the analogy of the malaria parasite favours the idea that in the insect it may grow to a visible size, and that although search in the blood for the cause of this grave disease hitherto has proved unsuccessful, it may yet be demonstrated in the tissues of the mosquito. Further, as several species of mosquito of the sub-family Anophelinœ have been shown to foster the malaria parasite, it is not improbable that several species of the genus Stegomyia may turn out to be effective intermediaries for the germ of yellow fever. *

Symptoms.— There is the same variety in the initial symptoms of yellow fever as in other specific fevers. There may be sudden rigor supervening in the midst of apparent health; there may be only slight chills; or there may be a period of premonitory malaise leading up to the more pronounced symptoms. When fairly started, the procession of events is rapid. Roughly speaking, and provided there are no complications, an attack of yellow fever is divisible into three stages 1, the initial fever; 2, "the period of calm," as it is called; and 3, in severe cases, the period of reaction.

The initial fever lasts usually from three to four days. The maximum temperature is generally attained within the first twenty-four hours, or by the second day, and, in a case of medium severity, may