846 IMMUNOLOGY 



crisis approaches and then rises thereafter. ) Furthermore, since parasites 

 reproduce at a high rate whenever they are found, it seems reasonable 

 to assume that they reproduce at a high rate during latency, when they 

 cannot be found in sufficient numbers to study. This assumption is in 

 accord with the view held by Ross (1910, review), Bignami (1910), 

 James (1913), and others. 



Essentially the same results were obtained from the studies of P. 

 brasilianum in Panamanian monkeys, except that during the crisis of 

 the initial infection (W. H. Taliaferro and L. G. Taliaferro, 1934a) 

 one asexual cycle may deviate or be retarded for a day or two. This 

 parasite shows a quartan periodicity. Thus in Figure 188 the percentage 

 of segmenters sharply increases and decreases every third day (4/28, 

 5/1, 5/4) until at the time the number crises is reached (5/7) the 

 percentage of segmenters does not rise as high as before and does not 

 decrease as precipitously. The other so-called benign malarias seem to be 

 similar, as far as the data on the following species go: P. cynomolgi, 

 in both Silenus rhesus and S. ivus; P. knoivlesi, in S. irus (Sinton and 

 Mulligan, 1933a, 1933b; Mulligan, 1935); and P. vivax and P. nialariae 

 in man. The rapidly fatal infection of P. knoivlesi in 5. rhesus is similar 

 to the acute rise of benign infections without a crisis. These statements 

 do not mean that temporary derangements of the cycle may not occur 

 during the crisis, as in P. hrasil'mnum; or after treatment with quinine, 

 as in P . cathemer'ium ( previously cited ) ; or after changes in host habits, 

 as has been shown to occur in both the latter species (L. G. Taliaferro, 

 1928; G. H. Boyd, 1929b; W. H. Taliaferro and L. G. Taliaferro, 

 1934b; and Stauber, 1939). 



Since there is no prolonged inhibition of reproduction, the number 

 curve can be interpreted chiefly in terms of parasiticidal effects. In other 

 words, the number of parasites after each asexual cycle should increase 

 by the number of progeny in each mature schizont (minus the number 

 of merozoites which develop into sexual forms), provided no death of 

 parasites occurs. The geometrical rate at which P. cathemerium increases 

 does not, however, account for all the progeny produced. They evidently 

 die at all stages of growth and segmentation (L. G. Taliaferro, 1925; 

 Hartman, 1927; Hegner and Eskridge, 1938) and die at a greater rate 

 during the latter part of the acute infection than during the early part 

 (Boyd, 1939). Hegner and Hewitt (1938) and Hewitt (1938) sug- 



