IMMUNOLOGY 



865 



and others. The fact that animals often die when trypanosomes are 

 scarce in their blood has been explained as being due to sugar depletion, 

 asphyxiation, toxins, and so forth (see von Brand, 1938, review). A 

 possibility that has not been adequately discussed in the literature is 

 that death shortly after a crisis may be due to the severity of the im- 

 mune reaction, comparable to that seen in overwhelming hypersensi- 

 tivity (cf. graph of malaria. Figure 188). 



In analyzing such infections, W. H. Taliaferro and L. G. Taliaferro 

 (1922) found that the basic rate of reproduction remains relatively 



250-1 



200- 



■a 



I wo 

 a 



22 24 26 

 Daijs iifter Injedioa 



40 42 



Figure 192. The changes in number of Trypanosoma rhodesiense and the coefficient 

 of variation during the course of infection in a guinea pig. As acquired immunity de- 

 velops, the parasites are killed by trypanolysins operative during the long chronic period 

 and at the two crises thereafter, but the rate of reproduction is not inhibited, as evi- 

 denced by the high coefficient of variation. (Redrawn from W. H. Taliaferro and L. G. 

 Taliaferro, 1922.) 



constant whenever parasites can be found in the blood in sufficient num- 

 bers for study. Thus in Figure 192 the coefficient of variation remains 

 between 8.5 and 12.0 percent from twenty-three through forty-three 

 days after infection. Knowles and Das Gupta (1928) corroborated 

 this finding for T, evansi in the rat, and Davis (1931) for T, rho- 

 desiense in the cat. There is some evidence that these trypanosomes, 

 when originally isolated in Africa, exhibit infections essentially simi- 

 lar, except that superimposed on the reproductive activity seen in 

 Figure 192 are intermittent periods of heightened reproductive activity. 

 Thus Robertson (1912) reported that periods of active reproduction of 

 T. gambiense in the monkey alternate with periods of less active repro- 

 duction. Since reproduction continues at a relatively high rate, even 

 during the periods of less active reproduction, and is never completely 



