MASTIGOPHORA 



749 



keratitis, and ultimately paralysis, leading to death in two to eighteen 

 months. 



The trypanosome is found most readily in the serous exudate from 

 the ulcers, as it is infrequent in the peripheral circulation; in this 

 respect it resembles the treponema of lues. The organism is about 

 twenty-five microns in length and possesses a clear cytoplasm, free 

 from granules, except when propagated in white mice, when they are 

 plentiful. 



FIG. 171. DOURINE. Showing swelling of genitalia and plaques on the skin. 

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

 2te Aufl., 1913.) 



Diagnosis ~by Complement Fixation. E. A. Watson, 1 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 are capable of convey- 

 ing the disease and yet remain normal in health and general appear- 

 ance, and this method of diagnosis is, therefore, invaluable. 



Watson obtains the antigen by inoculating a large number of 

 white rats with Trypanosoma equiperdum, collecting their blood when 



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



