82 THE ANIMAL PARASITES OF MAN 



ment of the trypanosome. Kinghorn and Yorke found that the 

 trypanosomes may persist in the fly, at an incomplete stage of their 

 development, for at least sixty days when the climatic conditions 

 were unfavourable. 



The first portion of the developmental cycle of the trypanosome 

 takes place in the gut of the fly. Invasion of the salivary glands of 

 the tsetse is secondary to that of the intestine, but is necessary for the 

 infectivity of the fly. A relatively high mean temperature, 75 to 

 85 F., is essential for the passage of the trypanosomes into the 

 salivary glands and the completion of their development therein. 



Kinghorn and Yorke 1 state that the predominant type of trypano- 

 some in the intestine of infected G. morsitans was a large broad form, 

 quite different from that which is most common in the salivary 

 glands. The trypanosome in the glands resembles the short form 

 seen in the blood of the vertebrate host. The authors quoted state 

 that both the intestinal and salivary gland forms of infective G. 

 morsitans are virulent when inoculated into healthy animals. 



Bruce and colleagues 2 have quite recently (June, 1914) published 

 an account of their investigations of T. rhodesiense in G. morsitans 

 in Nyasaland. (Incidentally it may be remarked that Bruce considers 

 T. rhodesiense to be identical with a polymorphic strain of T. brncei 

 see pp. 83, 94). The development of T. rhodesiense takes place in the 

 alimentary canal and salivary glands, not in the proboscis, of the 

 tsetse fly. In feeding experiments with laboratory bred flies, as 

 well as with a few wild flies, fed on infected dogs or monkeys, only 

 8 per cent, of the flies were found to be infected on dissection. Of 

 such infected flies, however, only some allow of the complete develop- 

 ment of the trypanosomes within them, in other words only about 

 i per cent of the flies become infective. The length of time which 

 elapses before a fly becomes infective varies from fourteen to thirty- 

 one days, averaging twenty-three days, when kept at 84 F. (29 C.). 

 The dominant intestinal type of flagellate in the fly is that seen in 

 the proventriculus, which contains many long, slender trypanosomes. 

 These proventricular forms find their way to the salivary glands, 

 wherein crithidial and encysted forms are seen. They change into 

 " blood forms," which are short, stumpy trypanosomes and are 

 infective. "The infective type of trypanosome in the salivary glands 

 corresponding to the final stage of the cycle of development is 

 similar to the short and stumpy form found in the blood of the verte- 

 brate host." The cycle is thus very similar to that of T, gambiense in 

 G. palpalis (fig. 30). 



CULTURE. J. G. Thomson (i9i2), 3 and subsequently Thomson 



1 Annals Trop. Med. and Parasitol. , vii, p. 281. 2 Proc. Roy. Soc., B, Ixxxvii, p. 516. 

 * Annals Trop. Med. and Parasitol., vi, pp. 103, 331. 



