196 MOSQUITOES OF NORTH AMERICA 
study the malaria of birds. As the result of work carried on from March to 
August, 1898, he completely demonstrated the life-history of a malarial organism 
in birds. He succeeded in infecting healthy birds by the bites of infected mos- 
quitoes, the species being identified as Culex fatigans.* Before this (in 1897) 
MacCallum of Baltimore had found that with Halteridium of birds the flagella 
and the pigmented spheres represented sexual forms of the parasite, the flagella 
impregnating the spheres. He was able to observe this process with malarial 
parasites of human blood. Thus the general law of infection and of the develop- 
ment of the malarial parasites was established. 
Grassi, approaching the subject from another viewpoint, conceived the idea 
that the disease and its transmitter must be coincident and that therefore the 
host relation of the malarial parasite is restricted to definite mosquitoes. He 
carried out most careful studies, which proved this to be the fact and showed 
that mosquitoes of the genus Anopheles alone are concerned in the trans-. 
mission of malaria in man. In 1898 Grassi, together with Bignami and Bas- 
tianelli, was working in Italy upon the malarial problem ; on November 28 they 
reported finding developmental stages of the malarial parasite in the stomachs 
of two Anopheles claviger, fed on patients with malarial crescents in their 
blood. On December 3, in the London Lancet, Bignami described the first suc- 
cessful infection (of a man named Sola) by an infected Anopheles. Later 
numerous valuable publications by the Italian investigators followed. Ross’s 
finding of the pigmented cells in Anopheles mosquitoes, in August, 1897, and his 
complete demonstration of the life-cycle of a malarial organism of birds, entitles 
him to the credit of the complete scientific demonstration of the relation between 
mosquitoes and malaria, a fact which, though still disputed by certain of the 
Italian school, has been recognized by most writers and has brought him the 
Nobel prize in medical discovery. To Grassi belongs the credit of the discovery 
that human malaria is only transmitted by Anopheles mosquitoes. Later work 
by investigators of many nations has resulted in an extensive knowledge of the 
life-history of the causative organisms of malaria, and a number of species be- 
longing to Anopheles have been proved to be secondary hosts of the malarial 
parasites of man. The Italian workers, Machiafava and Celli, and those above 
mentioned, Koch, and above all Schaudinn, of Germany, Laveran and Marchoux, 
of France, Manson, Ross, Daniels, and others, of England, have all contributed 
to the final results. It is perfectly demonstrated that the full development of 
the malarial parasite can not take place within the human body, and that certain 
species of Anopheles mosquitoes are the necessary secondary hosts, the sexual 
generation of the parasite taking place only in these mosquitoes. 
Some especial attention must be give to the work of Robert Koch on account 
of his large share in malarial investigation, not only from the scientific, but also 
from the practical side. In Italy, in the autumn of 1898, he was able to find the 
various stages of Proteosoma in birds and in mosquitoes. He succeeded in in- 
fecting mosquitoes by allowipg them to feed on birds harboring the parasites. 
Koch continued the ivetigon in Berlin, and in the middle of November fol- 
*=Culea quinquefasciatus Say. 
