ii6 INFECTIOUS AND PARASITIC DISEASES. 



but in the stomach of different species of mosquitoes 

 of the genus anopheles, which suck up the malarial 

 parasites when biting. In the mosquito's stomach, 

 coalescence (copulation) of the sexual elements occurs 

 and a new organism is formed. The new parasite in 

 turn forms other organisms in large numbers, which 

 pass from the mosquito's stomach to its body-cavity 

 and thence collect in its salivary glands ; from this situa- 

 tion they find their way into the blood of man again when 

 the insect bites. The forms thus inoculated give rise 

 to malaria. 



It has been definitely proven that malarial fever can 

 be conveyed in only one way, viz., through the bite of a 

 mosquito which harbors the plasmodium, and that only 

 species of the genus anopheles are capable of acting 

 as host to this parasite. Clinically the pathological 

 states resulting from invasion of the body by the pro- 

 tozoan parasites above described are not unlike those 

 of an infectious disease; indeed, we regard them as 

 belonging to the latter class, and would therefore include 

 the agents which cause them among the infectious 

 agents. They are placed among the parasites here 

 simply for convenience of description. 



NEMATODES. 

 FiLARiA Or guinea-worm, is a round worm which 



Medinensis develops in the subcutaneous tissues. 

 (Dracunculus Only the female is known. The worm is 

 medinensis). ^^^^^^ jj^^^ ^^i^ stomach probably through 



