MALARIA. 367 



cells, especially in those of the middle lobe, and also free in the ducts. 

 So numerous are they in some of the cells that the appearance they pre- 

 sent is suggestive of a bacillus-laden lepra-cell." 



The hypothesis that malarial infection results from the bites of mos- 

 quitoes was advanced and ably supported by Dr. A. F. A. King, of Wash- 

 ington, D. C, in a paper read before the Philosophical Society on 

 February 10, 1883, and published in the Populae Science Monthly 

 in September of the same year. In 1894, Manson supported the same 

 hypothesis in a paper published in the 'British Medical Journal' (De- 

 cember 8), and the following year (1895) Ross made the important 

 discovery that when blood containing the crescentic bodies was ingested 

 by the mosquito, these crescents rapidly underwent changes similar to 

 those heretofore described, resulting in the formation of motile fila- 

 ments, which become detached from the parent body and continue to 

 exhibit active movements. In 1897, Ross ascertained, further, that 

 when blood containing crescents was fed to a particular species of mos- 

 quito, living pigmented parasites could be found in the stomach walls of 

 the insect. Continuing his researches with a parasite of the same class 

 which is found in birds, and in which the mosquito also serves as an 

 intermediate host, Ross found that this parasite enters the stomach wall 

 of the insect, and, as a result of its development in that locality, forms 

 reproductive bodies (sporozoites), which subsequently find their way to 

 the veneno-salivary glands of the insect which is now capable of infect- 

 ing other birds of the same species as that from which the blood was ob- 

 tained in the first instance. Ross further showed that the mosquito 

 which served as an intermediate host for this parasite could not trans- 

 mit the malarial parasite of man or another similar parasite of birds 

 (halteridium). These discoveries of Ross have been confirmed by 

 Grassi, Koch and others, and it has been shown that the mosquitoes 

 which serve as intermediate host for the malarial parasites of man be- 

 long to the genus Anopheles and especially to the species known as 

 Anopheles claviger. 



The question whether mosquitoes infected with the malarial parasite 

 invariably become infected as a result of the ingestion of human blood 

 containing this parasite has not been settled in a definite manner, but 

 certain facts indicate that this is not the case. Thus there are localities 

 noted for being extremely dangerous on account of the malarial fevers 

 contracted by those who visit them, which on this very account are 

 rarely visited by man. Yet there must be a great abundance of infected 

 mosquitoes in these localities, and especially in low, swampy regions in 

 the tropics. If man and the mosquitoes are alone concerned in the prop- 

 agation of this parasite, how shall we account for the abundance of in- 

 fected mosquitoes in uninhabited marshes? It appears probable that 

 some other vertebrate animal serves in place of man to maintain the life 



