1086 



PATHOGENIC PROTOZOA 



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 an- 

 tigenic strength is standardized 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 avium. This parasite was first described by Dani- 

 lewski in 1885. In 1905 .Novy and .MacNeal 5 .found trypanosomes 

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

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



FIG. 138. TRYPANOSOMA AVIUM IN BLOOD OF COMMON WILD BIRDS. (After Novy 

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

 Blakiston's Son & Co.) 



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 

 and Hemorproteus ziemani with resulting confusion in the study of 

 trypanosomes and hemocytozoa, and it is only recently that the error 

 has been generally acknowledged. 



Trypanosoma gambiense (Sleeping Sickness). Two names have 

 been given to the disease caused by this parasite, both of which are 



9 Novy and MacNeal, Jour, Infect. Dis., Chicago, 1905, ii, 256. 



