RELATION OF INSECTS TO THE PARASITIC WORMS 69 



in the pupae and adult flics that developed from the larvae. This sug- 

 gested the possibility that flies having become infested as larvas might 

 convey the parasite to man by falling into or depositing their excreta 

 on food. Apparently these experiments have not been repeated. 



2. Parasitic Nematodes Whose First-stage Larvae Occur in the Blood or 



Lymph of the Final Host and Leave the Body Through Ingestion 



hy Bloodsucking Insects 



Filaria bancrofti Cobbold, 1877 



This important parasite of man is widely distributed throughout the 

 world in tropical and subtropical countries. It occurs in the United 

 States, thougii apparently it is by no means common. Historically it is of 

 special interest because of the fact that it is the species which Manson 

 (1878) showed passed through certain metamorphoses in the bodies of 

 mosquitoes after the larvse had been sucked up by these insects in the 

 blood of human beings affected with filariasis. Manson's researches 

 coupled with confirmatory work by other investigators established the 

 novel fact of the transmission of an animal parasite by a bloodsucking 

 insect, and may be taken as the starting point in the development of our 

 knowledge concerning the part played by such insects in the spread of 

 disease-causing organisms. Lewis had also observed the passage of the 

 larvas from the human host into mosquitoes. The first obsei'vation of 

 these larva? in man was recorded by Demarquay in 1864 in Paris, the adult 

 female was discovered by Bancroft in 1876 in Queensland, and the adult 

 male by Bourne in 1888. 



The adults of this species live in the lymphatic system, both vessels 

 and glands. The first-stage larvae which are provided with a thin cutic- 

 ular sheath, apparently the transformed egg shell, are found in the blood 

 stream, usually periodically as first shown by Manson, that is, in consid- 

 erable numbers only at night or rather during the hours of sleep, as the 

 periodicity may be reversed by making the patient sleep during the day 

 time. One of the names of the parasite, Filaria noctuma, is based upon 

 the periodicity of the appearance of the larvae in the blood. Various 

 pathological conditions have been attributed to Filaria bancrofti such as 

 adenitis, lymphangitis, abscesses, lymph scrotum, chyluria, and other 

 disturbances of the lymphatic system. The connection between filariasis 

 and elephantiasis is still a matter of argument among pathologists. 



When taken into the stomach of a mosquito the larvas lose their cutic- 

 ular sheaths. Within 24 hours they leave the alimentary tract, pass 

 into the body cavity, then into the muscles of the thorax. In the muscles 

 they become shortened to about half their original length and meanwhile 



