TRYPANOSOMA THEILERI 143 



and found that the long form had no free flagellum, but that 

 in the long and short forms the protoplasm extended to the end 

 of the flagellum. The parasites are found in small numbers (to 

 10 in a field of the microscope) in the peripheral blood, or are not 

 found for several days at a time. 



TRYPANOSOMA THEILERI 



The parasite, named Trypanosoma theileri, was found by 

 Theiler in 1902 in the blood of cattle. It is the largest of the 

 pathogenic trypanosomes, measuring 20-70 by 2-6 /a, and is di- 

 morphic. In the ordinary form (Theiler) the centrosome is situ- 

 ated at the posterior end of the body at some distance from the 

 nucleus; morphologically it resembles Tr. brucei except that it is 

 much larger. In the rarer form the centrosome is near or even 

 attached to the nucleus. This form is broader and shows ab- 

 normal shapes, — round, oval, lacerated, etc., while the nucleus is 

 larger and generally less compact. 



The parasites are most quickly found in living blood. They 

 are present in the blood a varying length of time. The longest 

 period observed by Theiler was 13 days, the shortest one day, the 

 average nine days. The number of parasites in 

 the peripheral blood varies a good deal. In one 

 case Theiler found 30 per field (objective No. 6 

 Zeiss); in other cases none could be found on 

 microscopical examination. Theiler considers 

 about five per field as a fair average. 



Frequently the parasites have been transmitted 

 in the process of immunizing cattle against 

 rinderpest, the blood injected containing the 

 trypanosomes. Theiler showed experimentally 

 that flies, Hippobosca rufipes and H. maculata, Fig. 22 - Tri J' 

 may transmit the disease. Tr. theileri is at pres- \™°°°l™ theileH 

 ent regarded to have very little if any pathogenic 

 properties. A similar trypanosome, perhaps the same species, has 

 been found in the blood of apparently healthy cattle in America. 



Changes in the blood. — The effect on the animal varies greatly. 

 In some cases no symptoms are produced; in others there is a 

 marked reduction in the number of red corpuscles. In one of 



