The Protozoa 133 



used in obtaining experimental proof for scientific theories ; and (4) it 

 brings home an understanding of the vast quantity of painstaking effort 

 necessary to obtain that proof. 



The malarial organism, Plasmodium malariae, is a member of the 

 class Sporozoa, nearly all of which are parasitic. It lives in the red 

 corpuscles (therefore called Haematozoa) of human blood where it 

 grows for a time, and then breaks up into from twelve to sixteen spores 

 which rupture the corpuscle. The corpuscle itself then breaks up into 

 tiny particles and the spores are thrown into the blood-stream. 



The malarial parasite has two life-cycles (Fig. 50), so to speak, one 

 the sexual cycle, which develops in mosquitoes, and the other the asexual 

 cycle, which develops in man. 



1. The sexual development of the malarial parasite within the body 

 of the mosquito takes from eight to ten days. These sexual forms are 

 known as gametes. 



The male cell (gamete) is also called a gametocyte. This gameto- 

 cyte develops from four to eight microgametes which force their way 

 into the large female cells (macrogametes). 



A sort of fertilization is thus set up. This fertilized cell is now 

 called a migrating cell or ookinete. The ookinete penetrates the stom- 

 ach-wall of a mosquito and builds a cyst (oocyst). Grassi says that 

 there may be as many as five hundred oocysts at a time in the stomach- 

 wall of a single mosquito. 



In the oocyst many tiny spherical bodies develop (sporulation). 

 These spherical bodies are the sporoblasts (primitive spore-cells) which 

 develop into thousands of sporozoites. These latter are merely tiny 

 filaments which get into the lymph system of the entire body of the 

 mosquito. As they reach the mouth-parts, they are ready to be injected 

 into any human being which the mosquito bites. Once inside man, they 

 enter the red-blood corpuscles and are known as schizonts (asexual 

 forms). 



From here on we must trace the asexual cycle of development in 

 man. The injected organism which has been placed in the blood-stream 

 of man is called a sporozoite. It finds its way into the red blood cor- 

 puscles and becomes rounded and more or less ring-shaped, while it is 

 amoeboid in movement. It is now a full-fledged schizont ( ). 



The schizont lives at the expense of the red corpuscle and deposits scat- 

 tered black or reddish, so-called melanin granules. These granules 

 should properly be called haematozoin granules ( ). 



The schizont now matures and becomes rosette-shaped when it is 

 known as the morula. Its nucleus breaks into daughter nuclei, or 

 rounded spores, known as merozoites ( ), the number 



of which may vary from six (in the Quartan fever parasite), to twenty 

 (in the Tertian fever type). 



The red corpuscle is finally broken up. This liberates the merozoites 



