FILARIA 159 



process of biting. Only inside man they work their 

 way to the lymphatics, and very soon the female 

 begins to pour into the lymph a stream of young 

 embryos, which reach the bloodvessels through the 

 thoracic duct. It is, however, the adults which are 

 the source of all the trouble. They are of considerable 

 size, three or four inches in length, and their presence, 

 by blocking the channels of the lymphatics, gives rise 

 to a wide range of disease, of which elephantiasis is 

 the most pronounced form. We can consider later 

 how the disease can be averted by keeping down the 

 number of gnats and by preventing their access to 

 infected patients. 



We now pass to the second of the diseases carried 

 by gnats, that of malaria. 



The parasite which causes malaria is a much more 

 lowly organized animal than the Filaria. It is named 

 Hcemamceba, and it, too, is conveyed by an insect, 

 and, so far as we know, by one genus of mosquito 

 only, the Anopheles. Hence, from the point of view 

 of malaria, it is important to know whether a district 

 is infected with Culex or Anopheles. The former is 

 rather humpbacked, and keeps its body parallel with 

 the surface it is biting, and its larva hangs at an angle 

 below the surface of the water, by means of a respi- 

 ratory tube. Anopheles, on the other hand, carries its 

 body at a sharp angle with the surface upon which it 

 rests, and its larva lies flat below the surface-film and 

 parallel with it. The malarial parasite lives in the 

 blood-cells of man, but at a certain period it breaks up 

 into spores, which escape into the fluid of the blood, 

 and it is at this moment that the sufferer feels the 

 access of fever. The presence and growth within the 

 blood-cells result in the destruction of the latter, a 

 very serious thing to the patient if the organisms be 

 at all numerous. If the spores be sucked up by an 

 Anopheles, they undergo a complex change, and ulti- 



