MASTIGOPHORA 



1085 



plasm, free from granules, except when propagated in white mice, 

 when they are plentiful. 



Diagnosis by Complement Fixation. E. A. Watson, 4 of Canada, 

 has shown that it is possible not only to diagnose the disease when 

 the clinical signs are clear, but also to determine the existence of 

 its non-clinical, obscure and latent forms. Horses may tolerate an 

 infection for one to three years, during which time they arc capable 

 of conveying the disease and yet remain normal in health and 



FIG. 137. DOURINE. Showing swelling of genitalia and plaques on the skin. 

 (After Kolle and Wassermann, "Handbuch der Pathogenen Mikro-organismen," 

 2te Aufl., 1913.) 



general appearance, and this method of diagnosis is, therefore, 

 invaluable. 



Watson obtains the antigen by inoculating a large number of 

 white rats with Trypanosomv, equiperdum, collecting their blood when 

 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 intraperi- 

 toneally, and at about the end of the third day, when the organisms 

 are very numerous, the rats are bled into citrate solution. By 



. A. Watson, Parasitology, Cambridge, Eng., 1915, VIII, 156. 



