Insects and Disease 633 



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 bancrofti, 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 



