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258 activities and propagation of the mosquito, and is probably also necessary for the evolution of the germ in the mosquito. Since the announcement of these discoveries many independent observers and several commissions have studied yellow fever in its relation to the mosquito, but, beyond confirming the results of the original American observers and adding some facts in the bionomics of S. fasciata, there has been no great addition to our knowledge of the subject. The germ itself is still unrevealed.

Marchoux and Simond have given us several new facts about the yellow-fever germ. They have shown that, although it is arrested by the Chamberland bougie B, it can pass bougie F ; that it will not infect if simply laid on a raw (blistered) surface; to secure infection it must be injected subcutaneously; that virulent blood-serum loses its virulence in forty- eight hours if exposed to the air at 24° to 30° C., but if protected by oil or vaseline will retain it for five days.

As regards S. calopus, the same observers note that to lay eggs she must first have a feed of blood, and that her eggs are deposited about three days after she has so fed. Before the first egg-laying, S.calopus is both diurnal and nocturnal in her feeding habits, biting at any time; subsequently she is strictly nocturnal in this respect. Therefore a stegomyia that bites during the day does not convey yellow fever. She is too young; any parasite she may harbour is immature. In this way is to be explained the impunity with which a yellow-fever centre may be visited during the day, although the visitor may be bitten by stegomyia. Europeans who live at Petropolis, a suburb of Rio de Janeiro, and are in the habit of visiting and transacting their business in the low-lying yellow-fever-haunted districts of the city, never contract the disease unless they are so imprudent as to pass the night in the latter. Marchoux and Simond further state that an infected stegomyia can communicate the yellow-fever germ to her eggs and so to the second generation of mosquitoes, and that