68o 



INFECTION BY THE BLOOD PROTOZOA 



I)ii/idingTrj|)ano^oine^ 



cytoplasm may be retarded so that the progeny from a single trypanosome may be 

 temporarily held together as a "rosette" (Fig. i). Schizogony which is characteristic 

 of the malarial parasites may be looked upon as a modification of binary fission. Here 



the nucleus undergoes a series of binary 

 fissions before the parent subdivides 

 ("sporulates") — thus a number of prog- 

 eny are produced at one time (Fig. 3). 

 If there is no resistance operative in 

 the host and reproduction is unimpeded, 

 the parasites whether they are reproduc- 

 ing by binary fission or schizogony should 

 increase according to a geometrical pro- 

 gression series (a, ar,ar,^ar,-'flr,4 .... ar,^ 

 for example, i, 2, 4, 8, 16, etc.). As will 

 be seen later, some infections follow just 

 this course of number increase, but the 



Groufth ^lage^ 



Adult Trypanosome^ 



Fig. I. — Trypanosoma leioisi. Top: Divid- 

 ing trypanosomes such as are found at the 

 height of reproductive activity. Middle: Growth 

 stages, taken from the fourth day of the infec- 

 tion shown in Fig. 7. (These are rarely found 

 after the tenth day of the infection.) Bottom: 

 "Adult" forms, taken from the twenty-eightli 

 day of the same infection. F, flagellum; N, nu- 

 cleus; P.B., parabasal body; t/.M., undulating 

 membrane. X 1,000. (Top, after Coventry; 

 others, after the author. 



Fig.' 2. — Trypanosoma eqiiiperdum. Dia- 

 grammatic representation of -.4 and 5, short and 

 long individuals resulting from binary division; 

 C, D, and£, stages in growth and division; and 

 F, cell division. X about 1,500. (Modified after 

 the author and L. G. Taliaferro.) 



majority do not. Sometimes, instead of 

 accumulating uniformly, the number of 

 parasites remains constant for certain 

 periods, or sometimes actually decreases, 

 from which it is immediately apparent 

 that some type of resistance is operative. 

 Number changes such as these demon- 

 strate the first method of analyzing the 

 effects of resistance, i.e., the number 

 curves of different infections indicate 

 whether any resistance is operative and 

 give an approximate measure of this 

 resistance. 



The number curve, i.e., the rate of 



