the malaria parasites of man; and by a similar discovery by Koch in monkeys. Similar parasites have also been found in the ox, sheep, dog, horse, etc. (b) The malaria parasite may be capable of passing from mosquito to mosquito without the intervention of a vertebrate, by passage of the sporozoite into the mosquito's eggs. We have the support of analogy for this hypothesis. Several Babesiœ, such as Babesia bovis, which gives rise to hæmoglobinuric fever (Texas fever) in cattle, and Babesia canis, which causes the malignant jaundice of dogs, are transmitted in this way. The intermediary, a tick, takes in the parasite with the blood it sucks from an infected animal. The parasite, probably after undergoing developmental changes, then passes into the egg of the tick, and so to the young tick hatched out from the infected egg; and it is this young tick that implants the germ into the next vertebrate host. In the case of the trypanosoma of the little owl, Schaudinn claimed to have shown that it may enter the eggs of the intermediary mosquito and that the infection may in this way be transmitted, not only by the mosquito that sucked the trypanosoma-containing blood but also by its progeny.
Most observers are now of opinion that the malaria parasite, under natural conditions, can be acquired by man only through the bite of the mosquito; that the mosquito can acquire the parasite only by ingesting the blood of a malaria-infected man or, possibly, other mammal; that there is no extracorporeal life other than that described; that there is no authentic instance of malaria being acquired in uninhabited places; that in the case of malaria in connection with soil disturbances it depends on the creation during digging operations of puddles of water in which mosquitoes breed; and that its epidemic occurrence under these circumstances is owing to unhygienic conditions, such as usually prevail when large bodies of men, some of whom may bring' the infection with them, are brought together on public works attended with extensive earth-cutting, as in railway, road, or canal making.
