Immunity and Resistance 637 



and so-called protective antibodies (probably opsonins). Precipitins (169) 

 and agglutinins (69, 110) also have been reported in other malarial in- 

 fections. 



Defensive mechanisms in trypanosome infections 



While it is possible to observe various antigen-antibody reactions 

 in vitro, the composite action on the parasite — the effect of the defensive 

 mechanism as a whole — can be comprehended only by the study of para- 

 site populations during infections. This method has been followed by 

 Taliaferro and his associates (171, 173) who have studied the development 

 of resistance in various host-parasite combinations. Growth of popula- 

 tions has been traced by counting the flagellates in blood samples at 

 intervals throughout the infections. Rate of reproduction has been esti- 

 mated by computing the coefficient of variation in length of the flagel- 



day s 



Fig. 14. 1. An acute lethal infection: Trypanosoma rhodesiense in 

 a mouse (after Taliaferro and Taliaferro). A relatively constant coef- 

 ficient of variation (C. V.) indicates a uniform rate of reproduction. 



