ETIOLOGY OF MALARIAL FEVER 75 



the same length as the proboscis, and in the male are 

 clubbed (fig. 22). 



(2) The scutellum, which is more or less trilobed in 

 other mosquitoes, shows no sign of such lobing in the 

 anophelines. 



(3) The scales on the veins of the wings are lanceolate 

 in the anophelines, whilst they vary greatly in the other 

 Culicidce (fig. 23). 



(4) The proboscis is nearly in the long axis of the 

 head, thorax and abdomen, so that the mosquito almost 

 forms a straight line. When at rest, as the proboscis 

 points towards the surface on which the mosquito rests, 

 the abdomen points away from it (fig. 24). 



(5) The larvae have no respiratory syphon ; they lie 

 flat on the surface of the water when at rest, and after 

 their first moult have compound " palmate " tufts along 

 each side of the abdomen on the latero-dorsal aspect. 



(6) The eggs are more or less boat-shaped, and have 

 lateral air-floats ; they are laid singly and not formed into 

 rafts. 



For the propagation of malaria all that is required is : 

 (i) That suitable anophelines should feed on a person 

 in whose blood sexually mature parasites gametocytes 

 are present ; (2) that these mosquitoes should be kept at 

 a proper temperature for a period varying according to 

 the temperature, from about eight to some sixteen days 

 o; more ; and (3) should then bite a person susceptible 

 to malaria. In about ten to fourteen days such a person 

 will develop malarial fever. As far as is known man is 

 the only animal that ever acts as the intermediate host 

 for the species of parasites which cause malarial fever 

 in man, and therefore mosquitoes, the definitive hosts, 

 derive the parasite from man only, and transmit it to 

 man only. Any break in the sequence will result in the 

 destruction of the parasites, and it is with this in view- 

 that all attempts at prophylaxis must be conducted. 



I. The parasites in man can be attacked by the use of 

 quinine in all infected persons, so that the chances of the 



