392 



ANIMAL BIOLOGY 



disease can, perhaps, be best illustrated by a brief outline of the 

 development of our knowledge of malaria, yellow fever, and 

 syphilis. 



Malaria. From ancient times malaria, as the name indicates, 

 was supposed to be due to foul air, especially from swampy regions, 

 but the first step toward the correct explanation was made in 1880 

 when Laveran found certain microscopic parasites always present 

 in the blood of malarial patients. Nearly two decades later Ross 

 demonstrated similar parasites in the body of a Mosquito, and 



Eggs 



CULEX 



Larva Pupa 



Adult 



ANOPHELES 



Rjihard t4«j Humoir 



Fig. 246. — Mosquito life histories. Mosquitoes of the genus Anopheles, 

 which transmit malarial parasites, differ from the common Culex in every 

 stage. When at rest the adult Culex holds its body parallel to the surface, 

 whereas Anopheles holds it nearly perpendicular. 



then a long series of studies by various investigators, among whom 

 Grassi stands foremost, showed that when a mosquito of the genus 

 Anopheles bites a malarial patient, it secures with the blood some 

 of the parasites such as Laveran had discovered, and thereupon 

 the mosquito becomes the host of the Malarial organism. Within 

 the mosquito, the parasite undergoes a complicated series of 

 changes, including rapid reproduction, This finally results in myri- 

 ads of parasites located in the sali v^ary glands of the insect, ready 

 to be injected into the blood of the next individual bitten and to 

 begin the other phase of its life history in Man. (Fig. 223.) 



So stated, it appears simple enough, but years of study by spe- 

 cialists on Insects (entomologists), by specialists on Protozoa 



