Immunity to Various Species of Trypanosomes. 



119 



intervals between them and the natural variations in the mice 

 employed. 



Against the parasites of surra of India, surra of Mauritius, 

 caderas, nagana, and a toluidin blue resistant strain of nagana, an 

 immunity was produced which was strong enough to prevent one 

 or more subsequent inoculations of virus from infecting. The im- 

 munity to dourine was less strong. 



In producing immunity to surra of India a single injection of 

 dichlorbenzidine plus amidonaphtol disulphonic acid, i, 8, 3, 6, 

 or " CI," was more efficient than one of acetylatoxyl or arseno- 

 phenylglycin. 



Even when the medicaments apparently prevented infection an 

 immunity was produced. It is interesting that two injections of a 

 mixture of " CI " and acetylatoxyl has completely protected a 

 normal mouse against an inoculation with surra of India given six 

 days after the second treatment. The mixture protected about 

 twice as long as either of its two constituents used alone had done. 



The immunity reaction distinguished with sharpness organisms 

 supposed to have had a common origin, namely, surra of India and 

 surra of Mauritius. Occasionally, however, these two species im- 

 munized against each other. With equal clearness the reaction 

 distinguished between organisms known to have had a common 

 origin, e. g., the toluidin blue resistant strain and the parafuchsin 

 resistant strain. When mice were immunized to the toluidin blue 

 trypanosomes, an inoculation with the same virus failed completely, 

 while the tests with the parafuchsin resistant strain and with all 

 others, infected and killed. 



By means of the immunity reaction it was apparently possible 

 to separate in purity organisms that had been mixed in vitro. By 

 inoculating a mixture of surra of India and surra of Mauritius into 

 mice immune to surra of India an infection with surra of Mauritius 

 was obtained. The surra of India was separated by inoculating 

 the mixture into mice immune to surra of Mauritius. In a similar 

 way caderas and surra of India were separated. 



When mice infected with a mixture of two species of trj'pano- 

 somes were cured, an immunity to both was produced. 



In securing prolonged specific immunity, frequent injections of 

 the virus at close intervals were of value. A mouse cured of 



