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Also a disease (or diseases) called by the natives ruhinyo, muhinya, enya-enya, and bihimbo, the names being, apparently, used indiscriminately and interchangeably, has received attention. An epidemic called by one or more of these names had been reported from Ankole, and, when Dr. Bagshawe arrived at Lake Albert Edward to investigate the epidemic there, about the only facts that he could gather were that there certainly was an epidemic, and that it was called ruhinyo.

Since, therefore, ruhinyo or muhinya had been rumoured to exist in the interior of Toro as well as in Ankole, and I had already instructed Dr. Lowsley, the Medical Officer of the latter province, to investigate it there, Dr. Bagshawe was at once directed to examine the inland epidemic of Toro. Dr. Bagshawe thinks, and I agree with him, that there is little room for doubt that the epidemic which he then examined is beri-beri, a disease new to our experience in this country, and I append hereto his very careful and interesting report, with extracts from his later reports and also from those of Dr. Lowsley, whose description of the cases which he saw in Ankole is inconclusive, but bears some resemblance to severe dengue, a disease which was epidemic this year in the Protectorate.

I had hoped that an enquiry, as to whether Glossina morsitans and other tsetse flies can convey Trypanosoma gambiense could have been commenced ere this, but it has been found necessary to postpone it. It will, however, in all probability be undertaken shortly.

It is a matter of very grave importance, and especially so in the Nile Province, where, as I found during my term of residence, both Morsitans and Pallidipes are present, and, in some places, abound. They are to be found, probably co-extensive, from Northern Unyoro to the northern border of the Protectorate, and how far beyond this I am unable to say, but they become more plentiful just where Glossina palpalis has its limit, and, if unfortunately they can convey the infection, the epidemic may spread into the Sudan. My own belief is, however, that they will not prove to be natural carriers.

In my report already quoted (Note I.) I pointed out that there is no continuous "fly-belt" across the Uganda Protectorate, but the Glossina palpalis exists in certain circumscribed strips of narrow patches along the margins of lakes, rivers and streams. These areas I proposed to call " fly-areas," and the limit of flight from the waterside (Note 2)* at such places the "fly-range," reserving the term "fly-belt," which had been very loosely used, and had no well-defined meaning, to describe the limits of distribution across the continent. I have already used these terms above and I propose to adhere to the definitions throughout this report.

I also showed that the fly-areas and fly-ranges, both of which are local and vary with the locality, are much narrower than had previously been supposed; that, far from inhabiting swamps, the fly rather avoids them, and is absent or scanty on the true shore, even if shaded, behind wide belts of swamp, while it is practically never met with on swamps pure and simple nor on swamp-filled rivers and streams (which I shall call hereafter, for the sake of brevity, "swamp rivers"); that the conditions most suitable to them are open water, however small in extent, contiguous shade and a certain amount of raised or definite bank. I recorded also the fact that Glossina palpalis was present on most or all of the inland streams which are open, with running water, wherever there was sufficient shade, and that, in the case of very narrow streams, this might be afforded sometimes by high or over-hanging banks or even by long grass.

I described how it is probable that in most cases sleeping sickness is conveyed from place to place by man, especially along main traffic routes, and from man to man, in suitable localities, by the fly; how in any epidemic area the local intensity of infection varies with certain physical and geographical conditions such as indented coastline, peninsulas, islands, rivers, swamps, shade, cliffs, open water, &c., which affect the fly, and how these conditions again interact with others, which chiefly concern the human inhabitants, to determine the magnitude of an epidemic and the direction of its spread, these last conditions being, chiefly, density of popula- tion, relation of dwellings and occupations to local fly-ranges and the methods and frequency of intercommunication; and I showed how certain localities within or

• NOTE 2.—In the term "fly-range" the limits of flight along the water's elge are not taken into consideration. Flight in this direction may reach to long distances and is limited by local conditions. See page 16 below and also Appendix B.

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in contact with fly-ranges are reciprocally infective, while others, beyond the fly- range, can be infective only via the fly-ranges, the chances of the spread of infection varying with the distance therefrom and the frequency and facility of communication therewith; also that it is possible for settlements well outside the local fly-ranges, if so situated as to be in frequent and easy communication with them, perhaps on several sides (as often happens in an island or a peninsula), to show a very high percentage of infection among their inhabitants, although the transmission of infec- tion is impossible within their precincts, and I attached diagrams to illustrate these points and also to show the probable method of extension of the Lake Victoria epidemic, the most probable connection between it and the Lake Albert and Nile epidemic and the probable direction of spread in the near future.

I will now give a short summary of what the various medical officers engaged in the extended investigations have recorded.

All agree that the haunts of Glossina palpalis are close to open water with shade, especially that of undergrowth and 'scrub. Dr. Bagshawe notes that the banks are often steep and generally have a decided slope. Dr. Densham mentions that most of the inland streams on which the fly abound (which are always open, flowing streams) have steep or definite banks. Dr. Wiggins describes a peculiar distribution on the Mpologoma River (which is so extensive that it more nearly resembles a great lake, the greater part of which is choked with sudd), where fly is absent on the numerous creeks, which run inland often for miles, choked with swamp and having no definite banks, while, in the few places where it is present, it is found on the true shores or those parts or points nearest the main body of the lake where, in all probability, the banks would be comparatively firmer and higher and there is more likelihood of the existence of patches or strips of open water at the sites of ferries, landings and dipping-places. Dr. Van Someren describes one of the few inland streams in his district on which fly was present as having very well-defined banks. We may take it, then, that the essentials of a typical fly-area are more or less open water, with contiguous and especially overhanging shade, preferably of scrub (though in very narrow streams high banks or even high grass may be sufficient), and a certain amount of fairly well-defined bank or shore, this last being essential, in all probability, for the breeding-grounds.

All the medical officers agree as to the absence or only occasional presence of fly on the true shore behind wide belts of papyrus or other luxuriant and close- growing swamp-vegetation, even though this shore may be well shaded and other- wise favourable to it, but they differ as to the width of such a belt necessary to ensure its absence. Dr. Van Someren found in his district that 30 yards and upwards was sufficient, and that flies are seldom seen either on the lake or shore side of such a belt, while the only width of belt mentioned by Dr. Wiggins behind which fly was absent is 100 yards. No doubt the necessary width varies in different localities and with other factors such as the abundance of flies, the amount and kind of food supply, the existence of canoe or other traffic through it with neigh- bouring fly-areas from which a certain number might be "imported," and with the length or extent of the belt along the shore or bank.

All are agreed that if, as occasionally is the case, especially where the sudd or swamp has floated in from elsewhere and has not grown out from a low, swampy shore, there remain patches or strips of open water at the true foreshore behind the swampy-belt, fly may be found at these places if the other conditions are favour- able to it, but that on the outer margins of even a moderately wide belt the fly is not found. Narrow belts of papyrus or other such vegetation are not antagonistic to the fly, nor are open reeds, nor other small or sparsely-growing water-weeds. I may add that the presence of ambatch-bushes at the true shore or in the water near it, since other vegetation seldom penetrates them to any great extent, always means the existence of a little comparatively open water, and is thus favourable to the fly, but by no means an invariable sign of its presence.

All are agreed that Glossina palpalis does not exist on swamp-rivers; and it is either absent or very scanty on the swampy parts of comparatively open rivers. Since practically all the inland waters of Uganda proper, Buddu, South and East Unyoro, and Western Usoga are of this nature, the very important fact remains that practically the whole interior of these regions is fly-free, and therefore "safe," country. The only notable exception to the above rule is part of the main trunk or basin of the Mpologoma which, as has just above been mentioned, is really a lake. There are also streams in South Usoga, apparently of a swampy nature, on some

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