PROTOZOAN PARASITES 



293 



Plasmotomy. — Plasmotomy is the term applied to the inter- 

 mediate division of the cytoplasm of multinuclear parasites into 

 two or more masses, which afterwards may or may not reproduce 

 by spore-formation. 



3. Spore-Formation. — Instead of being considered a process of 

 internal gemmation, the formation of pansporoblasts may be 

 looked upon as a process of spore-formation proceeding while the 

 organism grows, as is typically seen in the Neosporidia. 



The typical asexual spore-formation or schizogony is, however, 

 met with in the Telosporidia, in which the early stages absorb 

 nutriment and increase in size, being therefore called trophozoites. 

 When fully grown they form a quiescent body, the schizont, 

 whose nucleus and cytoplasm divide into a number of small 

 "orms called asexual spores or merozoites, generally, however, 

 eaving a little undivided cytoplasm laden withgefEete matter, 

 hich is called a nucleus de reliquat, or ' rest body.' 



Fig. 43. — Schizogony of Plasmodium vivax Grassi and Feletti. 

 (After Schaudinn.) 



I, Young trophozoite; 2, ring form; 3, ring form showing hsemozoin; 

 , parasite with pseudopodia ; 5, old trophozoite; 6, schizont showing com- 

 mencement of first division; 7, schizont with four nuclei; 8, schizont with 

 several nuclei (the corpuscle shows Schuffner's dots) ; 9, schizont divided into 

 merozoites; 10, merozoites and haemozoin free. 



These merozoites are the forms by which the parasite multiplies 

 in the given host, and are not the means by which new hosts are 

 infected. They therefore enter new cells in the host in which 

 they are formed, and, growing into a trophozoite, complete an 

 asexual life-cycle, which is called the cycle of schizogony, or simply 

 schizogony (Fig. 43). 



A time arrives in the infection of every host when the food 

 material for the given parasite is diminished by the numbers of 

 forms produced by asexual reproduction, or when the tissues of the 

 host react against the parasite by chemical substances, or phago- 

 cytosis, or by both methods combined. 



When these adverse circumstances become sufficiently severe, 

 changes take place in the parasite which produce forms capable of 

 leaving|thejgiven host and existing outside it, either in a different 

 species of animal or simply in the exterior, until an entry is made 



