392 
Mammalian Trypanosomes of Africa 
with the descendants of the trypanosome which was parasitic in man at the 
time of the epidemic. A careful watch will be kept over the reinstated natives, 
and more especially over the fishermen, who will in this case also provide 
a natural experiment on a large scale. 
(23) The reintroduction of man into the fly area, without careful pre¬ 
cautions against re-establishing that close contact between man and insect 
which prevailed in the old days, would, in my opinion, lead eventually to the 
reappearance of human trypanosomiasis. Under the present scheme, however, 
the contact between man and fly is reduced to such an extent that, even if 
the existing organism is still capable of surviving in man, there will be no 
chance of the disease spreading. On the Mpologoma the disease still occurs 
endemically, and it is no great distance from this centre to the great lake; 
but every effort will be made to avoid the introduction of a fresh supply of 
human trypanosomes into the repopulated area. The scheme for carefully 
controlled repopulation of the fly zone will not fall to the ground even if 
sporadic cases of trypanosomiasis occur among the returned populations. The 
contention is that, with proper organisation, these areas can once again play 
their part in the economy of the Protectorate, without the mortality from 
this cause amounting to a serious figure. 
(24) The indication recently forthcoming from Damba, that certain of 
the wild trypanosomes are developing increased virulence in laboratory 
animals suggests a far-reaching train of thought concerning the phylogeny 
of this group of organisms. As has been pointed out above, the Sesse Islands 
present a picture unparalleled in fly bionomics in Africa. G. palpalis is here 
in the closest contact with an antelope, and is undoubtedly feeding very 
freely on this mammal in spite of the existence of reptilian hosts. The chief 
mammalian host of the polymorphic trypanosomes of Damba at the present 
day is undoubtedly the situtunga, just as the chief hosts of these trypanosomes 
in morsitans areas are the game animals. The present close relations between 
fly, trypanosome, and antelope on Damba have steadily developed since 
1909, and, at the present time, are closely parallel to those obtaining in typical 
big-game and morsitans country, always excepting the presence of reptiles. 
It is possible , therefore , that the prolonged sojourn of a polymorphic trypanosome 
exclusively in game animals through many generations iyiay result , per se, in the 
assumption by the parasite of the characteristics of the trypanosome known as 
T. brucei, irrespective of the tsetse species concerned with its transmission. 
(25) The foregoing considerations suggest that the differences between 
T. gambiense and T. brucei depend upon the predominance in T. gamhiense 
areas of hosts other than ruminant game, i.e. man and possibly the hippo¬ 
potamus and reptiles also. On this assumption is explained the failure to 
recognise the brucei type of trypanosome in pure palpalis areas elsewhere in 
Africa; for nowhere else have extensive observations been made in an area— 
if indeed such exists—where the removal of man has led to G. palpalis be¬ 
coming closely and almost exclusively associated with antelope as a source of 
