436 RESEARCH IN PROTOZOOLOGY 



fections. Particularly is this true of certain trypanosome and 

 malarial infections where the entire life cycle occurs in the blood 

 stream and representative samples can be obtained from the 

 peripheral blood. 



By making daily number counts of such blood protozoa and 

 studying the resulting number curves, various types of infections 

 can be differentiated in experimental trypanosome and malarial 

 infections. The simplest condition is seen v^hen the parasite re- 

 produces at a constant uninterrupted rate and the organisms ac- 

 cumulate in the blood stream according to a geometrical pro- 

 gression series until the host dies. Such an uninterrupted increase 

 of the organisms can be modified by one or both of tw^o anti- 

 bodies, i.e., the parasites may be destroyed by means of lysis or 

 phagocytosis after they are formed, or reproduction (cell division) 

 may be inhibited by means of a reproduction-inhibiting anti- 

 body. 



The reproduction-inhibiting property of serum (W. H. Talia- 

 ferro, 1924) inhibits the reproduction of the parasites and is 

 brought about by the action of immune serum. As it has only been 

 carried out in in mvo experiments, whether or not complement is 

 necessary has not been ascertained. It diflfers from lysis in that 

 there is no affinity between antigen and antibody in vitro (i.e., 

 the antibody does not sensitize the antigen). 



A. Trypanosomiasis and avian malaria. The effect of these 

 various processes may best be illustrated by specific examples 

 which are taken from reviews by the author (1926, 1928, and 

 1928a). The simplest type of infection is encountered when the 

 pathogenic trypanosomes are grown in the mouse where no demon- 

 strable antibody whatever is developed, as evidenced by the 

 constant reproductive rate and the steady accumulation in numbers 

 of parasites. 



When the same trypanosomes are grown in the guinea-pig, rat, 

 rabbit, dog, etc. (W. H. and L. G. TaHaferro, 1922) or when 

 the bird malarial parasite is grown in the canary (L. G. Taliaferro, 

 1925), a parasiticidal resistance is formed as evidenced by the 

 unchanging rate of reproduction throughout the infection in con- 

 junction with the irregular but periodic number crises. In the 

 trypanosome infections the parasiticidal resistance has been shown 

 to be a lysin {in vitro by Schilling, 1902; Lingard, 1904; Franke, 

 1905; Rodet and Vallet, 1906; Massaglia, 191 1 and 1912; and 



