IMMUNOLOGY 



867 



serial transfer, since it has been found that strains remain immunologi- 

 cally unchanged for long periods in mice. The trypanosomes which re- 

 populate the blood after each trypanolytic crisis are immunologically 

 different from the passage strain and are resistant to the lysin produc- 

 ing the crisis. They are known as relapse strains and also have to be 

 maintained in mice by serial transfer. Thereafter, as many relapse strains 

 as are studied have to be extracted and maintained separately and con- 



12 14 Z 4 

 Datjs after [n|9Ctloii 



12 14 



Figure 193. The demonstration of a trypanolysin against a passage strain of Trypano- 

 soma equinum by passive transfer. An artificial crisis is produced in the trypanosome 

 infection in the experimental mouse, which received 0.3 cc. of serum taken from the seed 

 guinea pig after its infection had undergone a crisis, whereas the infection in the control 

 mouse which was not given serum proceeded uniformly until the mouse died. (From 

 W. H. Taliaferro and T. L. Johnson, 1926.) 



tinuously until the investigation is terminated. Reference to Figure 193 

 will make this clearer. Both the guinea pig and the two mice were in- 

 fected at appropriate intervals with a passage strain. Serum taken from 

 the guinea pig at the time of the naturally occurring crisis produced an 

 artificial crisis when injected into the experimental mouse, but would 

 have been ineffective had the experimental mouse been infected with 

 the relapse strain, which would have repopulated the blood of the 

 guinea pig after the crisis. (The artificial crisis produced by the immune 

 serum in this so-called curative test is very temporary.) A brief resume 

 of the investigations follows. 



