Immunity and Resistance 643 



the rate of reproduction dropped 25-50 per cent before the first crisis. 

 After the crisis, the division-rate rose again and became fairly constant, 

 but usually failed to reach the original level (Fig. 14. 6). The malaricidal 

 rate also varied. During the first day, 50-60 per cent of the parasites were 

 destroyed after each merogony. Three or four days later, the rate reached 

 90 per cent or higher and then remained at about this level. In similar 

 fashion, the malaricidal rate in P. knowlesi infections in monkeys in- 



8- 

 7 

 6- 

 5 



M 



3 



2^ 



parasites/lOO red cells 



m/s 

 20 



10 



% 

 90 



70-1 



50 



30 



10 



10 



15 



days 



Fig. 14. 6. Plasmodium cathemerium in a canary (after G. H. Boyd). 

 The rate of reproduction is indicated by the average nuinber of merozoites 

 produced by each schizont (m/s). The death rate is expressed as percentage 

 of parasites destroyed in each merogonic cycle. 



creases from about zero to approximately 90 per cent in acute infections 

 (183a). 



The primary factor in the malaricidal mechanism is phagocytosis; 

 the lymphoid-macrophage, or "reticulo-endothelial," cells play the domi- 

 nant role. Although it was once believed that phagocytes are mainly 

 scavengers in malaria, the evidence indicates that normal parasites are 

 ingested (174, 188). Indirect evidence also has been obtained by splenec- 

 tomy and by blockade of the tissue phagocytes. The latter procedure 

 involves the injection of material Avhich is ingested by phagocytes and 

 subsequently interferes with phagocytosis of parasites. Splenectomy in 

 monkeys with chronic or latent infections is often followed by relapse, 



