Insects and Disease 
6 33 
length of three feet. Other species vary from an inch to a foot in length. 
All the species of the genus Filaria are parasites of other animals living 
mostly in the stomach and intestine, sometimes in the connecting tissue and 
elsewhere in the body. One species lives in the heart of dogs, another in 
the body-cavity of the horse, donkey, and ox, still another in the eyes of 
negroes in West Africa, while Filaria bancrojti , the particular species 
which is the cause of filariasis, lives in the blood and lymphatic vessels of 
men in tropic lands of both Old and New World. The young or larval 
filariae (sometimes called F. sanguinis-hominis) live in the blood, but they 
finally lodge in the lymphatic glands and there mature. 
The most common form of filariasis is called elephantiasis. The presence 
of the parasite in the lymphatic glands and vessels leads to a subcutaneous 
hypertrophy of tissue which often results in a most frightful malformation 
of parts of the body. The legs and arms are particularly affected, and such 
a member may become of enormous size and be hideously repulsive in appear¬ 
ance. A single leg may come to weigh as much as all the rest of the body. 
An arm may become a foot thick, the fingers being mere papillar-like processes 
at the end of it. In Samoa fully one-third of the natives are attacked by this 
disease, which is incurable, and, though slow in development and nearly 
painless, certainly fatal. 
Manson, to whose keen inductions much of the credit for the discovery 
of the relation between the mosquito and malaria is due, was the first to 
suggest, on a basis of some observation and special investigation, that the 
mosquito is the secondary or intermediate host of the elephantiasis-producing 
filariae and that the mosquito is probably responsible for the dissemination 
of the disease. 
The subsequent researches of Manson, Bancroft, and others have proved 
that the filariae actually do live in the bodies of mosquitoes, being taken into 
the alimentary canal with the blood sucked from men affected by the disease. 
These filariae work their way through the walls of the alimentary canal and 
gather in the thoracic muscles. Here they live for some time, two or three 
weeks probably, and are then ready for their further development in the 
blood and lymph of man. Exactly how this transfer is made is not definitely 
proved as yet, although much evidence has been secured to show that the 
transmission is made by the mosquito-bite. Manson suggested that the 
female mosquitoes coming to reservoirs, ponds, or puddles of water to lay 
their eggs would often die there so that their bodies would fall on to the sur¬ 
face of the water. As they disintegrated by rapid decay, the larval filariae in 
the thoracic muscles would escape into the water, and live there until taken into 
the alimentary canal of people drinking some of the water from the reservoir 
or pond. Bancroft believes, however, that the filariae are transmitted by 
the bite or puncture of the mosquito, and has actually observed the migration 
