WILLIAM H. TALIAFERRO 



6gi 



The immunological basis of the first effect of resistance has been studied by the 

 author (1924) and seems 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 method of demonstrating the presence of this property is shown in Figure 8 



SeedRal 97 2 



ETperimenlal Ral 977 - 





2 4 6 8 

 Ddijs after Injedioa 



K 14 



Fig. 8. — Graphs demonstrating the passive immunization of an uninfected rat with the reproduc- 

 tion-inhibiting reaction product which has been formed in an infected rat. Note that after reproduc- 

 tion had been inhibited in seed rat 972, one half of its adult trypanosomes, plus a suitable amount of 

 its serum, was injected into experimental rat 977, while the other half of its trj^anosomes, plus an 

 equal amount of serum from a normal rat, was injected into control rat 980. Subsequently, in experi- 

 mental rat 977 the normal cycle of reproduction was altered— there was a complete inhibition of 

 reproduction as evidenced by the coefficient of variation; whereas in control rat 980 the normal cycle 

 of reproduction took place. (The peak in the number curve of control rat 980 is so much higher than 

 that of seed rat 972 because it received an enormously larger number of parasites initially.) (.'\fter 

 the author.) 



which is typical of numerous experiments carried out by the author and confirmed 

 by Coventry (1925) and Regendanz and Kikuth (1927). On the tenth day after 

 infection (when the trypanosomes had reached the adult stage) a rat (seed rat 972, 

 in figure) was killed and bled and its serum containing the adult trypanosomes col- 

 lected. Next, the trypanosomes were separated from the serum by rapid centrifuga- 

 tion. Then half of the adult trypanosomes together with 2 cc. of the serum (per 

 loo-gm. rat) was injected into experimental rat 977 while the other half of the trypa- 

 nosomes together with a similar dose of normal rat serum was injected into control 

 rat 980. Daily examinations of blood smears and calculations for the coefficient of 



