708 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1909. 
taneous labors of Bancroft on the one hand, and of Manson and Low 
on the other. 
These indefatigable investigators proved that if a man bitten by a 
mosquito was affected by filariasis, the embryoes taken in with the 
blood reached the stomach, the walls of which they at once traversed 
in order to lodge in the mass of the thoracic muscles. They remained 
twenty days in this situation, and were there transformed into larve, 
and then passed into the pharyngeal cavity of the insect. Thence 
they proceeded one by one into the proboscis, which inoculated them 
with every bite, in the same manner, conse- 
quently, as it inoculated the malarial plasmodium. 
The Culicidz responsible for this transmission 
belong to the genera Anopheles and Culex. The 
same thing happens in the case of the filaria of 
the dog, Filaria immitis, which lives in the heart 
(fig. 4). Grassi and Noé established the fact 
that this worm was, like the preceding, conveyed 
by Culex and Anopheles, in which it accom- 
plished an evolution comparable to that of the 
Filaria bancrofti, except that the embryoes were 
transformed into larve not in the thoracic 
muscles but in the malpighian tubes. 
The same course is pursued by the following 
species: F%laria recondita, which lives in the 
fatty perirenal tissue of the dog, and is propa- 
Fic. 4.—Embryos of 22ted by fleas and also, it is true, by a tick, RAd- 
Filaria immitis of the picephalus siculus; Filaria perstans of the con- 
Baa Wee ees nective tissue of the base of the mesentery of man, 
. ~ which is common in Guiana and West Africa, and 
which, according to Feldmann, may be transmitted also by a tick 
which has been described but not named; Pilaria labiato-papillosa 
of the peritoneum and eye of cattle, eh is inoculated by flies 
closely allied to the common fly, the Stomox; Filaria medinensis, 
which lodges in the subcutaneous connective tissue of man, the horse, 
ox, and dog, and which is not conveyed by an insect, but by small 
crustaceans, the Cyclops. 
C. YELLOW FEVER. 
Yellow fever is a disease of man which belongs to the category of 
maladies called diseases due to invisible, or ultra-microscopic, mi- 
crobes, because the latter are so small and attenuated that often 
they can not be discerned by the aid of the most powerful objectives. 
The most extraordinary suppositions have been made regarding the 
origin of this terrible disease. The celebrated experiments made in 
