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complete in twenty-four hours. If at the end of that time another animal should come along the fly will settle on it, but it is not yet hungry, and so is in no hurry to bite. Such a fly may follow a caravan of porters (or presumably a herd of game) and be carried several miles beyond the fly-belt. At Ruwe fly was occasionally seen fourteen miles from the nearest permanent fly. Nevertheless, these following flies disappear and the enlargement of fly-belts does not appear to be due to this cause. Forty-eight hours after a meal a fly is hungry again and would probably bite at once, and so would not be carried far.

The statement the fly follows the is almost certainly incorrect if it game means that when the game treks the bulk of the fly, or a large proportion of the fly, of the district treks with it. The bulk of the fly remains behind. This was well illustrated in my recent visit to Sipani Vlei. In the dry season this is a noted place for game, but when I arrived after the rains had begun the animals were scattered. All I saw was about a dozen zebra and two or three mpala. Walking out in the gusu I went several miles, and saw nothing but a herd of sassaby and fresh spoor of a small party of elands. If I had gone a fortnight earlier I should, no doubt, have seen several herds of animals in or near the vlei. But though the animals were gone the fly was numerous close to the water, though in the gusu there was very little. The fly had not followed the game. It was waiting there, and would, perhaps, be gradually dispersed by stray animals, and a good number would probably wait and

starve.

It is true, however, that the parts of a fly-belt where game is numerous are the parts where most fly is to be found, and the reason would seem to be that where blood is plentiful the fly live and breed; where it is scarce many die, and the females will either be barren or breed slowly.

There is no evidence that the fly has any alternative food besides blood, and I only know of one competent observer (Major Stevenson-Hamilton) reporting fly present in a district where there was no game.

Conclusions as to aetiology of the sickness.

Anyone who has seen sleeping sickness of the Congo has only to look at a map showing the distribution of human trypanosomiasis in Rhodesia to realise that the two diseases are spread in quite a different way. In the Congo the sickness is worst where the population is thickest, it attacks both sexes and all ages (though it seems The Rhodesian disease appears to to run a more rapid course in young people). attack almost exclusively the men in a small and scattered population, and infection seems to take place far away from the village.

The obvious conclusion is that the wild game is the reservoir of the disease. In Northern Rhodesia Kinghorn and Yorke have found Trypanosomiasis Rhodesi- ense in 16 per cent. of the game animals, which seems to prove the case for that country. In this country the direct proof is lacking, but the known facts point irresistibly in the same direction.

Suggestions as to Prophylaxis.-I believe that the intention of the Adminis tration is to move all natives out of the fly area. It seems that this can easily be done, and it would certainly stop the sickness for a time. The question that occurs is- will not such a measure lead to the undisturbed increase of the game and the fly, joint carriers of the sickness? Then may we not expect the fly to spread, and in a few years reports of sickness from another group of villages and more removals? On the other hand, any measures that may be undertaken against the fly or the game would be obviously more costly and difficult in a depopulated country where neither labour nor food could be obtained.

Certainly the most satisfactory method would be to devise some means of reducing the number of tsetse, but we have no knowledge of how to do this. Clearing of the breeding places has been suggested, but it is only quite recently that a few breeding places have been found, and the latest reports of Mr. Lloyd in North-Eastern Rhodesia seem to indicate that the clearing would be a long and difficult business!

There remains destruction of game. There is some dispute as to whether the fly does or does not disappear when the game is destroyed. I myself think that it does, but however that may be, if it be the truth that the game is the reservoir of the sickness, it follows that a fly which has not fed on the blood of game would not be infective.

I am entirely in sympathy with those who view with regret the destruction of the wild game, and that is why I advocate shooting and frightening the animals

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away from a small area now rather than from a larger area a few years later; for I am convinced that this is the plan which will ultimately be adopted. I have dis- cussed the objection that the fly follows the game," and that, therefore, to drive the game out of the fly-belt would spread the fly.

The reports so far received from the Mafungabusi fly area seem to indicate that human trypanosomiasis is not to be found there.

It has been suggested that there might be a danger of driving infected game from the one fly area into the other. The distance between the two areas is over 60 miles. The danger, if it exists, would be avoided by simultaneous action against the

game in both areas.

(Annexure 5.)

PAPER READ TO THE ROYAL ZOOLOGICAL SOCIETY BY DR. WARRINGTON Yorke.

THE RELATIONSHIP OF THE BIG GAME OF AFRICA TO THE SPREAD OF SLEEPING SICKNESS.

Although sleeping sickness has been recognised as a disease on the West Coast for nearly two hundred years, human trypanosomiasis was unknown in Nyasaland and in the greater portion of Rhodesia until 1908. At the end of this year the first case of the disease was found in Nyasaland, and during 1909 and 1910 a considerable number of cases were discovered amongst the Europeans and natives living in Nyasaland and Rhodesia. This state of affairs was not easy to understand, as the particular tsetse fly, Glossina palpalis, which is known to transmit sleeping sickness in other parts of tropical Africa has not been found in these countries.

In 1910 it was shown that the parasite causing the disease in Nyasaland and Rhodesia differed in certain respects from that causing sleeping sickness in other portions of tropical Africa. The name Trypanosoma rhodesiense was given to this new parasite.

Since these discoveries many cases of sleeping sickness have been found in Rhodesia and Nyasaland, and in 1911 the Chartered Company decided to have the matter thoroughly investigated; it was with this object that Dr. Kinghorn and I were sent to North-Eastern Rhodesia.

The first problem that we had to solve was to ascertain the vector responsible for the spread of sleeping sickness in a country where Glossina palpalis does not exist. Now, although Glossina palpalis has not been found either in Nyasaland or in the Luangwa Valley of Rhodesia, yet Glossina morsitans, the tsetse fly which is known to cause "fly" disease in domestic stock, is present in enormous numbers, and it was soon proved by Dr. Kinghorn and myself that it is this fly that iɛ responsible for the spread of human trypanosomiasis. This discovery is one of great practical significance; for whereas the former fly, Glossina palpalis, is limited in its distribution to water-courses, and never found far from the banks of certain rivers or the lake shores, the latter, Glossina morsitans, is ubiquitous, its distribu- tion being quite independent of water. Hence, it is at once obvious that it is impossible to attempt to deal with sleeping sickness in Rhodesia and Nyasaland by any such simple method as removing the native population back from the water- courses and lake shores--a procedure which was attended with such remarkable results in Uganda. The problem of preventing the spread of sleeping sickness in these countries, which a few years ago were thought to be in no danger, is one of infinitely greater difficulty than was that which had to be faced in Uganda.

A large number of wild Glossina morsitans were examined in the Luangw Valley in order to ascertain what proportion were capable of infecting man with trypanosomiasis. This information is important as it affords an approximate idea of the potential danger of the district. We found that one in five hundred wild Glossina morsitans were infective in nature. This is an astonishingly large proportion; and

it is at once evident that some host other than man must be infected with the human trypanosome in order to account for the large number of naturally infective Glossina morsitans. With the object of ascertaining what was the chief vertebrate reservoir of the virus, we examined a large number of the wild fauna of Africa. In all, we examined 250 wild animals (including elephant, rhinoceros, hippopotamus, lion, buffalo, fourteen different kinds of antelope, caracal, galago, squirrel, genet, hunting dog, giant rat, and wild rabbit), 256 monkeys, 35 domestic stock, 142 wild rats,

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