634 Insects and Disease 



of the filariae from the thoracic muscles forward into the head and "beak" 

 of the mosquito. He has seen a filaria larva issuing from a fine opening 

 near the tip of the labium. According to Bancroft's theory the filaria 

 escapes from the beak of a puncturing mosquito into the skin of a man, 

 finishes its development and growth in the skin, becomes adult, pairs and 

 produces embryos which get into the lymphatic spaces or vessels, and are 

 carried by the lymph into the blood. Here they circulate over the body, 

 finally lodging in the lymphatic glands and causing the characteristic hyper- 

 trophy of tissue. Further investigation is necessary, however, before the 

 question of transmission is fully understood. That the mosquito is the 

 actual disseminating agent of the disease is, however, certain. 



The species of mosquito which acts as intermediate host and distributing 

 agent of the filariae in Australia is Culex fatigans, var. skusii. Anopheles 

 rossii is also known to carry the filaria;. In Samoa, where elephantiasis 

 is more prevalent than anywhere else in the world, I have found the most 

 abundant mosquito to be Stegomyia fasciata, the same species that spreads 

 yellow fever. This species is also the most abundant mosquito in the Hawaiian 

 Islands, and is indeed wide-spread over the tropics and subtropics of the 

 whole world. If, as is probable, it is the principal carrier in Samoa of the 

 filariae that cause elephantiasis, it is the most formidable single species among 

 all the insect scourges of mankind. 



In this brief account of the role played by certain insects in the propa- 

 gation and dissemination of certain human diseases only a small part of the 

 story, as already known, has been told. Cockroaches, bedbugs, and other 

 household insects are being found to be hosts for the germs of other familiar 

 diseases. A host of investigators is at work; reports of discoveries are being 

 published constantly, and in a few years our knowledge of this causal rela- 

 tion of insects to human disease will fill books instead of chapters. 



