H. L. Duke 387 
In the total of infected flies nourished on monkey blood in these parallel 
experiments the infective fly of Exp. 94 is not included. 
Taking by themselves the positive flies in the paired experiments with 
the human strain we have: 
on reptile blood: Total flies dissected ... 213 
Containing flagellates ... 1; 
on monkey blood: Total flies dissected ... 190 
Containing flagellates ... 7; 
i.e. 0-46 per cent, as against 3*68 per cent, infected flies on reptile and monkey 
blood respectively. 
Mangabey sp.: 
Mangabey.Number of flies dissected after the 19th day ... 134 
Flies containing flagellates ... ... • • • 2 
Ordinary species ... Number of flies dissected after 9th day ... 142 
Flies containing flagellates ... ... • • • 1 
These dissections, limited though they are, indicate that a continued diet of 
blood of this resistant species does not harm the developing flagellates. 
The number of flies used in these experiments is unfortunately small; it 
is hoped to continue investigations on these lines on my return from leave. 
(e) Conclusions as to the effect of reptile blood on 
developing trypanosomes. 
As far as conclusions are warranted by the limited evidence it seems that 
reptile blood exerts a relatively unfavourable influence on polymorphic try¬ 
panosomes developing in laboratory-bred G. palpalis. This unfavourable effect 
is especially noticeable in the case of the human strain of trypanosomes. 
Flies can, however, become infected and infective on such a diet. 
PART VI. GENERAL REVIEW AND SUMMARY. 
A consideration of the above experiments, and of the available literature 
dealing with the distribution of trypanosomes and tsetse flies in nature, has 
suggested certain general conclusions which will now be put forward. 
(1) Glossina palpalis is essentially not a game tsetse in the sense that 
G . morsitans and G. pallidipes are. Its main food-animals, undei primitiv e 
African conditions, are reptiles, possibly birds, man and his stock, the hippo¬ 
potamus, and such game animals as may visit its haunts. 
(2) In inhabited regions, wherever the wild G. palpalis are known to carrj 
a polymorphic trypanosome with “anterior station” in the salivary glands, 
cases of trypanosomiasis of the gambiense type will generally be found to occur 
in man. The polymorphic trypanosomes so far recovered from game, stock, 
and man in inhabited palpalis areas, fall into line rather with T. gambiense 
