862 IMMUNOLOGY 



bodies which are associated with the globuhn fraction of immune serum, 

 are passively transferable, and are probably a product of the lymphoid- 

 macrophage system; but whereas ablastin possesses no in vitro affinity 

 for the trypanosomes, the trypanolysins are typical antibodies (ambo- 

 ceptor) and can sensitize the trypanosomes in vitro. Furthermore, the 

 macrophage system does not appear to intervene in the passive transfer 

 of ablastin, but in some way functions in the union of antigen and anti- 

 body during the passive transfer of the trypanolysins. 



CONTINUOUS FATAL TRYPANOSOMIASIS IN THE MOUSE AND SOMETIMES 

 IN THE RAT 



Most species of trypanosomes appear to be nonpathogenic, and there 

 is a growing mass of evidence that even many of the pathogenic forms 



_ Millims or Trypanosomes per ctnm. of blooa 

 Cosfficien cf Variation 



Figure 191. The changes in number of Trypanosoma rhodesiense and the coefficient 

 of variation during the course of infection in a mouse. No acquired immunity is de- 

 veloped in the mouse, since the number of trypanosomes more or less steadily increase 

 and their rate of reproduction, as evidenced by the high coefficient of variation, is not 

 inhibited. (Redrawn from W. H. Taliaferro and L. G. Taliaferro, 1922.) 



in man and domesticated animals may be nonpathogenic in their natural 

 hosts (cf. Duke, 1936). Little is known of the course of their infection 

 in their natural hosts, but they have been extensively studied in labo- 

 ratory animals, in which they are all pathogenic. The well-known patho- 

 genic trypanosomes, which produce disease in man and domestic ani- 

 mals, are T. gamhiense, T. rhodesiense, T. brucei, T. congolense, T. 

 vivax, T. evansi, T. equiniim, and T. equipevdum. When injected into 

 mice, the parasites almost invariably appear in the blood after a short 

 incubation period, and increase in number more or less steadily until 

 the death of the host. This type of infection is composed of an incuba- 

 tion period and acute rise, with no crisis or developed infection. It 

 sometimes occurs in the rat. Its continuous nature was clearly pointed 



