THE PROTOZOA AS PARASITES OF MAN 155 



It is known as the sporont on account of its further history, 

 which is as follows. 



Through its thin cyst-wall the parasite continues to absorb 

 nutriment, and grows in size, bulging out the wall of the 

 stomach into the body cavity so as to form a kind of blister. 

 As it grows, its nucleus multiplies by binary fission and cyto- 

 plasm becomes concentrated round each nucleus to form a 

 body known as a sporoblast. Now the nucleus of each 

 sporoblast divides repeatedly and the surface of the body 

 grows out into slender processes, into each of which one of 

 the daughter nuclei passes. Finally the processes break off, 

 and the cyst contains hundreds of needle-like sporozoites to- 



Fig. 96. — Part of the alimentary canal of a mosquito infested with 

 Plasmodium. — From Lankester's Zoology, after Ross. 



O^Cysts of the parasite ; int., intestine ; M.t., Malpighian tubes; ces., oesophagus ; 

 st., stomach. 



gether with some residual protoplasm. The ripe cysts burst 

 and scatter their contents into the body cavity of the insect 

 host, from which the sporozoites pass into the salivary glands. 

 In these the mosquito secretes a liquid which is injected 

 into its prey when it bites, and has the effect of stimulating 

 the blood-flow. When next it feeds, the little parasites pass 

 with the saliva along the proboscis into the blood of the 

 man on whom the mosquito is feeding, there to bore their 

 way into red corpuscles and start a new infection. 



Long after apparent recovery from an attack of malaria, 

 a patient may suffer a recurrence of the disease. It is 

 uncertain whether this be due to persistence of a few of the 

 trophozoites or to female gamonts acting somewhat as the 

 " latent bodies " of trypanosomes. 

 n 



