TRICHINA, HOOKWORMS, FILARIA, ETC. 85 



ment these larval forms must be taken into the alimentary 

 canal of a mosquito. There they undergo certain changes, 

 and then make their way through the walls of the stomach 

 into the muscles, where they increase in size until they are 

 about one-sixteenth of an inch in length. Later they migrate 

 to other parts of the body, some of them to the proboscis of 

 the mosquito from w r hich they issue when the mosquito is 

 feeding and thus gain entrance into another host. It is not 

 known that these parasites can gain an entrance into the 

 circulatory system in any other way, 

 but it has been suggested that mosqui- 

 tos dying in the water may liberate 

 some of the filariae which may later 

 find their way into the vertebrate host 

 when the water is used for drinking. 



Soon after entering the circulatory 

 system of the human host the parasites 

 make their way into the lymphatics 

 where they attain sexual maturity, 



and in due time new generations of F IG. 29. Microfilaria 

 ,v i i i r-i of the blood; immature 



the larval filariae, or microfilanae, are stage of Fila ' ria bancroflL 



poured into the lymph, and finally (Greatly enlarged; after 



into the definite blood-vessels, ready Terzi -) 



to be sucked up by the next mosquito that feeds on the 



patient. 



In most cases of infection the presence of these filariae in the 

 blood seems to cause no inconvenience to the host. They 

 are probably never injurious in the larval stage, that is, in the 

 stage in which they are found in the peripheral circulation. 



In many cases, however, the presence of the sexual forms in 

 the lymphatics may cause serious complications. The most 

 common of these is that hideous and loathsome disease known 

 as elephantiasis, in which certain parts of the patient become 

 greatly swollen and distorted. An arm or a leg may become 

 swollen to several times its natural size, or other parts of the 

 body may be seriously affected. This disease occurs most 

 commonly in tropic and sub-tropic regions. Nearly one-third 

 of the natives of the Samoan Islands suffer from elephantiasis. 



