ON THE LIFE-HISTORY OF FILARIA IMMITIS. 255 
integument of the labium; he had an idea of his own to 
explain their exit from the labium. As is well known, 
when a mosquito imbibes blood, the labium or sheath of the 
stylets is bent upon itself, whilst the stylets are thrust 
deep into the skin; Grassi considered that when a labium 
containing filarize was thus buckled up it would be ruptured 
and the worms extruded. This hypothesis was easily dis- 
proved, for upon microscopic examination of the labia of 
filariated mosquitoes, which had bitten and relieved them- 
selves of parasites, one or more openings were seen in the 
labellee, often very apparent owing to the escape of pigment 
and granular matter; there were no openings elsewhere. 
It remained to be proved by actual experiment, that filari- 
ated mosquitoes could infect dogs, and it was important to 
ascertain how long a time would elapse before embryo- 
filarize could be detected in the experimental dog’s blood. 
The time taken from the bite of the mosquito until the 
embryos can be found in the blood is about nine calendar 
months; in one instance it was only eight and a half months. 
One dog, which had been filariated, was stolen at eight 
months, up to which time there were noembryos in its blood. 
To fix the time as accurately as possible, this experiment 
was made: a puppy, bred from non-infected parents, was 
kept away from filariated dogs; on December 30th, 1902, 
it was put into the mosquito house and 183 filariated 
mosquitoes, three weeks old, were liberated; the next morn- 
ing it was found that 70 mosquitoes had bitten; that was 
the only infection the dog received. After seven months 
had elapsed, its blood was examined weekly, but it was not 
until October ist, 1903, i.e., nine months, that the embryos 
were detected; the dog was then killed and the heart and 
lungs examined, there were 32 fully developed filariz, six- 
teen males and sixteen females, in the right ventricle and 
pulmonary artery. 
