328 BIOLOGY: GENERAL AND MEDICAL 



system, grow to maturity, and later fill the blood with 

 their own embryo-descendants. 



This discovery led Manson to suspect that the malarial 

 parasite might have a similar intermediate, and experi- 

 ments with mosquitoes showed him that when blood 

 containing malarial parasites was taken into the mos- 

 quito's stomach-intestine, the parasites underwent a 

 change known as flagellation, which was suspected to be 

 the beginning of a new life cycle. Manson was not able to 

 perfect this work, but his pupil, Ross, acting upon his 

 suggestions, worked patiently upon the problem in 

 India and succeeded in showing that certain mosquitoes, 

 the genus Anopheles, do act as hosts of the parasites. 



Fio. 122. Filarial worm (a) in proboscis of Culex pipiens. 



The last step in a complete understanding of the life 

 history of the parasites was made by MacCallum in 

 this country. 



In brief, the life history is as follows: The parasites 

 live one cycle in the body of man, where they first appear 

 as minute amoeboid bodies in the red blood corpuscles. 

 These grow and destroy the corpuscles until they attain 

 to an almost equal size, when they divide into a varying 

 number of small bodies or spores (the parasite belongs 

 to the class Sporozoa of the Phylum Protozoa). These 

 spores at once attach themselves to other corpuscles and 

 repeat the phenomena of growth and sporulation and so 

 on, a new crop maturing every third or fourth day 



