640 Immunity and Resistance 



In either case, reproduction of the flagellates (as indicated by the coeffi- 

 cient of variation and the percentage of divising forms) is rapid at first 

 but shows a sharp decline after the first few days and has practically 

 ceased within two weeks. Throughout the rest of the infection, there 

 seems to be no further reproduction, although the persisting flagellates 

 remain infective for normal rats (1 7 la). 



This inhibition of reproduction is attributed to the appearance of an 

 antibody, ablastin, which prevents fission without destroying the trypano- 



600 



500. 



400 



300 



thousands/mm^ 



CONTROL 



10 



day s 



Fig. 14. 4. The effect of ablastin on development of Trypanosoma lewisi in 

 tfie rat. The experimental animal ^\'as inoculated with T. lewisi suspended in 

 serinii containing ablastin; the control, Avith a comparable inoculum of trypano- 

 somes from the same source but suspended in normal serum. 



somes. Ablastin serum, transferred to non-immune rats (Fig. 14. 4) pro- 

 duces the same effect (167). The importance of ablastin in defence against 

 reinfection has been questioned by Augustine (5), who observed dividing 

 flagellates in immune rats after massive intraperitoneal inoculation with 

 T. lewisi. If these dividing flagellates were not present in the inocula ot 

 200-900 million T. lewisi, or if there was a significant increase in dividing 

 forms after inoculation, it would appear that ablastin is relatively 

 inactive against reinfection by this route. On the other hand, the data 

 of Becker and Lysenko (16) are in accord with the view that ablastin 

 and trypanolysin are separate antibodies. At any rate, ablastin (or the 



