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X] shore of Lake Victoria Nyanza to fly-free areas in the interior. It was hoped that, the human source of trypanosome supply being thus denied them, the tse-tse flies would cease to be infective. Unfortunately, this hope has been disappointed. Three years after depopulation of the districts involved, Bruce ascertained that the local flies could still convey the disease to laboratory animals. Manifestly, T. gambiense can flourish under natural conditions in vertebrates other than man. The large game is now regarded as a probable reservoir for T. gambiense, as it is known to be for the T. brucei of nagana.

The introduction of T. gambiense into other countries is a grave possibility. It is true that it must have been frequently introduced into America in the days of slave importation and that it did not spread there; but as regards India and other Asiatic countries, which hitherto have had little or no communication with the West Coast of Africa, no introduction on a large scale has occurred, and we have no assurance that, if introduced, the parasite would not find some appropriate transmitter. According to some authorities, nagana and surra are the same disease; if so, the causal trypanosome can be transmitted by blood-sucking flies other than the tse-tse. What holds good for T. evansi and T. brucei might equally apply to T. gambiense. Furthermore, the possibility of the introduction of the fly host of the trypanosome of sleeping sickness, G. palpalis, into other tropical countries must not be lost sight of.

The discovery by Stephens and Fantham that the trypanosome found in sleeping-sickness cases originating in Nyasaland and Rhodesia presented certain peculiarities when passed through the rat, that it was associated with a highly virulent and resistant form of the disease,* that animals immunized against T.gambiense succumbed to the Rhodesian trypanosome,