PARASITIC WORMS 285 



ORGANISMS TRANSMITTED BY BLOOD- 

 SUCKING FLIES. 



The discovery, which first clearly demonstrated 

 that flies may act as carriers of parasitic micro- 

 organisms, was made by Manson in 1878. It had 

 been known for several years previous to this date 

 that in China and other tropical countries the 

 young stages of a small parasitic worm, known as 

 Filaria bancrofti, were present in the blood of some 

 individuals. These young worms are the progeny 

 of parents living in the internal organs. Sometimes 

 they are present in the blood during the day and 

 disappear at night, and in other patients the reverse 

 is the case. For further development the young 

 worms require to be ingested by a mosquito, when 

 the latter is sucking the blood of the patient. The 

 young worm soon bores its way out of the stomach 

 into the muscles of the mosquito, where it passes 

 through various stages in its development. About 

 the eighth day the worms make their way into 

 the proboscis of the mosquito and remain there 

 till the mosquito bites a man, when they pass out 

 onto the skin through which they bore and make 

 their way into his body. 



A similar disease of dogs is transmitted in the 

 same way. 



The investigations on Yellow Fever may be 

 quoted at some length for several reasons. The 



