264 The Philippine Journal of Science — 1921 
” How they, in their sheaths, manage to maintain their posi- 
tion in the larger vessels against the blood stream is as yet 
unexplained. 
So far we have dealt with the parasite in its human host; 
now we must deal with its progress through its intermediate 
host. 
By artificial means it is quite possible to make the filarial 
embryo cast its sheath. One of the best ways is to lay the 
preparation in an ice box overnight. When the slides warm 
up next day, wherever the blood has become laky, the filarize 
endeavor to break through their sheaths, and in a short time 
they succeed in doing so and move very freely about the slide. 
After the blood has passed into the mosquito’s stomach, the 
same proceeding takes place. A few hours after feeding, this 
can be easily observed, and in another few hours the mosquito’s 
stomach is found to contain only the empty sheaths. Where 
have the filarie gone? As soon as they lose their sheaths, 
they become able not only to move about freely, but also to pierce 
the stomach wall. 
They are found to have passed into the muscles of the mos- 
quito’s thorax. There they undergo a metamorphosis lasting 
some sixteen to twenty days, a proceeding which has for its re- 
sult the formation of a mouth, an alimentary canal, a peculiar, 
trilobed tail, and finally a parasite much grown in size and 
activity. The metamorphosis being completed, they pass for- 
ward for the most part to the cephalic region, a few only 
passing backward into the tissues of the abdomen. 
From the head they pass often in pairs into the proboscis, 
and are conveyed thence into the human host when the 
mosquito bites. They lie in the proboscis between the under 
surface of the hypopharynx and the upper surface of the labium, 
extended in the loose connective tissue of the latter. 
As far as my researches go, in at least 95 per cent of the 
cases especially examined for eliciting the source of infection 
there was either a near relative, or a neighbor, or some one of 
the same village to be found as a possible source. But there 
were also cases like that shown in Table 5. 
In this case the mother had lived with the father for at 
least twenty years after he started elephantoid fever, but she 
had never suffered from any form of filarial disease. Her blood 
was quite free from the parasite. The sons, who were infected 
and noninfected, had always lived together and slept two in one 
bed and three in another. The two infected ones had acquired 
