750 



PATHOGENIC PROTOZOA 



teeming with trypanosomes, and separating them from the erythro- 

 cytes and plasma by washing and centrifuging. Each of ten to twenty 

 rats receive 0.3 c.c. of blood rich in trypanosomes intraperitoneally, 

 and at about the end of the third day, when the organisms are very 

 numerous, the rats are bled into citrate solution. By repeated washing 

 the organisms may be separated, as a pure white layer overlying the 

 erythrocytes. This mass of organisms is killed and preserved by a 

 formalin-glycerin mixture, after which its antigenic strength is stand- 

 ardized by titration in the usual way. The test, a pure culture of 

 trypanosomes being used as antigen, is specific and is not positive 

 in any other disease of horses. 



Trypanosoma avmm. This parasite was first described by Dani- 

 lewski in 1885. In 1905, Novy and MacNeal * found trypanosomes 



FIG. 172. TRYPANOSOMA AVIUM IN BLOOD OF COMMON WILD BIRDS. (After Novy 

 and MacNeal. MacNeal, "Pathogenic Microorganisms," published by P. Blakis- 

 ton's Sons & Co.) 



in 8.8 per cent of 431 American birds. Although there are doubt- 

 less several species, the most common is Trypanosoma avium, a para- 

 site twenty to seventy microns long and four to seven microns wide. 

 They are found in the blood over long periods of time and do not 

 appear to be pathogenic. Cultures are easily made and kept alive 

 for long periods by weekly transfers. The mode of transmission is 

 unknown. 



This was the parasite which was confounded in 1904 by Schaudinn 

 with developmental stages in the life cycle of Hemorproteus noctuce 



1 Novy and MacNeal, Jour. Infect. Dis., Chicago, 190.5, ii, 256. 



