IMMUNOLOGY 843 



and, to be satisfactory, necessitate a nice adjustment between the validity 

 of the criteria selected and the time required to make measurements. 



The most convenient measure of the rate of reproduction of the 

 Plasmodia so far devised consists in ascertaining the length of the asexual 

 cycle directly (i.e., the time it takes for a young merozoite to become a 

 mature schizont and divide into the next generation of young mero- 

 zoites), in conjunction with the number of merozoites produced. Thus 

 the percentage of segmenters are computed in samples of 50 to 100 

 parasites from stained blood smears made every 4 to 12 hours whenever 

 parasites can be found. A regularly recurring percentage of segmenters, 

 considered arbitrarily, for example in P. brasilianum, to have 5 or more 

 nuclei by W. H. Taliaferro and L. G. Taliaferro (1934a), indicates a 

 constant rate of reproduction, provided the number of merozoites pro- 

 duced by each segmenter remains approximately constant. The most 

 satisfactory measure of the rate of reproduction among the trypanosomes 

 consists in comparing the percentage of division forms in samples of 

 50 to 100 forms from stained blood smears made every 6 to 24 hours 

 throughout an infection. Among the pathogenic trypanosomes, in which 

 dividing forms are numerous, division forms may simply be considered 

 as those with some duplication of parts (see Krijgsman, 1933), but 

 among the nonpathogenic Trypanosoma leivisi and T. duttoni, in which 

 actual dividing forms are rare, division forms are considered to be 

 dividing forms plus short young forms 25 p or less in length (see W. H. 

 Taliaferro and Pavlinova, 1936). The higher the percentage of division 

 forms among the trypanosomes is, the higher the rate of reproduction. 

 Valid measures have also been devised for malaria by L. G. Taliaferro 

 (1925), G. H. Boyd (1929a), Lourie (1934), and Mulligan (1935); 

 and for trypanosomes by Robertson (1912), Krijgsman (1933), and 

 W. H. Taliaferro and L. G. Taliaferro (1922). The last authors' coeffi- 

 cient of variation method depends upon the fact that, within certain 

 limits, the variability in total length increases proportionately as the 

 young and growing forms resulting from reproduction increase. 



MALARIA 



This analysis applies only to those malarial species which parasitize 

 erythrocytes and not to such species as Plasmodium elongatum (Huff and 

 Bloom, 1935), which undoubtedly infect other blood and connective 



