SEROLOGICAL METHODS IN THE STUDY OF PROTOZOA 437 



in vivo by Diesing, 1905; Kleine and MoUers, 1906; the author 

 and Johnson, 1926; and Johnson, 1929). In the avian malarial 

 infection it has been shown not to be a humoral antibody (W. H. 

 and L. G. Taliaferro, 1929), but is associated with a heightened 

 activity of the reticulo-endothelial system (Cannon and W. H. 

 Taliaferro, unpublished). 



When the non-pathogenic T. lennsi is grown in the rat (W. H. 

 and L. G. TaHaferro, 1922; Coventry, 1925; and Regendanz and 

 Kikuth. 1927), and guinea-pig (Coventry, 1929), both types of 

 antibodies are formed as manifested by the retardation and final 

 inhibition of the rate of reproduction about the tenth day in both 

 animals, coupled with the two definite numlier crises (one at ap- 

 proximately the tenth day and the other at the termination of 

 the infection in the rat) and the scarcity of parasites throughout 

 an infection in the guinea-pig. The basis for the inhibition of 

 the rate of reproduction (as studied by W. H. Taliaferro, 1924 

 and Coventry, 1925), has been found to be due to the acquisition 

 of an immune property, by the serum of infected rats, which 

 inhibits cell division but which does not kill the parasites. The 

 first number crisis on about the tenth day in the rat has been 

 found to be due to a passively transferable trypanocidal property, 

 probably a lysin (Coventry, 1929) as has also the second number 

 crisis which terminates the infection (MacNeal, 1904; Manteufel, 

 1909; W. H. TaHaferro, 1924; Coventry, 1929), with phagocytosis 

 possibly playing a subsidiary role (Laveran and Alesnil, 1901 ; and 

 Regendanz and Kikuth, 1927). 



The methods used in this work consist in ascertaining: (i) what 

 type of number curve a given infection shows, and (2) whether 

 the reproductive activity remains constant or changes. Thus, to 

 cite one possibility, if the reproductive activity remains constant 

 while the number of parasites decreases (or even remains at a 

 level), a parasiticidal mechanism is operating. 



The number curve is easily found by getting the proportion 

 of parasites and red blood cells per cubic centimeter at fre- 

 quent intervals. 



Among the trypanosome infections, the reproductive activity 

 is obtained indirectly by ascertaining the coefficient of variation 

 for total length of samples of parasites from daily blood smears 

 throughout the infection, because if reproduction is rapid, there 

 will be a great variability in size, but if it does not occur, there 



