TRYPANOSOMA THEILERI 501 



cattle were at once transferred to uninfected animals, and in two cases 

 out of four an infection resulted. Such a transmission, if it actually took 

 place, is evidently a purely mechanical one, which might be accomplished 

 by any biting insect. The difficulty of excluding an infection in the cattle 

 apart from the culture method, which was not employed by Theiler, 

 raises doubt as to whether the experimental animals were really free from 

 infection before exposure to the flies. 



Noller (1916) succeeded in obtaining a culture on blood-agar of Cri- 

 tJiidia suhulata, a flagellate first described by Leger, L. (1904c), from the 

 gut of Tabanus glancopis, and, owing to the resemblance of the cultural 

 forms to those of T. theileri, he came to the conclusion that C. suhulata is 



Fjg. 211. — Tahatms Uvniola (T. soeius) (?) of the Sudan, with Wings extended 

 (x2-5). (After King, 1911.) 



This species very commonly harbours a crithidia, which is probably a developmental form of 

 Tryfanosoma theileri. 



really the developmental form of T. theileri in the tabanid fly, which is to 

 be regarded as the true insect host of this trypanosome. It has been 

 suggested above (p. 358) that C. hyalommce, which occurs in the tick, may 

 possibly be a developmental form of this trypanosome. If C. suhulata 

 is merely the insect phase of T. theileri, it seems probable that this applies 

 also to other similar flagellates of Tabanidse and their allies, such as those 

 seen by the writer (1909) in the Sudan. They were especially common in 

 Tahanus tceniola {T. soeius), which was a voracious blood-sucker (Fig. 211). 

 Noller (1925) appears to have established this identity in the case of the 

 crithidia of Hcematojpota pluvialis. He injected clean calves with cultures 

 of the flagellate of the flies and recovered trypanosomes from the blood 

 by culture on the fifth, sixth, and tenth days. 



