PUBLIC RECORD OFFICE
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C.O.885
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18 PUBLIC RECORD OFFICE, LONDON
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Owing to the situation chosen no direct sunlight fell on the place of observation after 3 p.m., when it was found that no flies were obtainable. These counts show fairly well the influence both of weather and of the time of day.
Investigations have also been made into the numerical proportions of male to female flies in various fly-areas, which varies greatly, and probably bears some rela- tion to the breeding-season (if there be such), or to the proximity of the breeding- grounds, or to both. In most cases males have predominated, and Dr. Bagshawe is He is inclined to the only observer in whose experience the reverse was the case. think that females are more numerous where human (vertebrate?) blood is easily obtained, and that they wander further than do the males in search of food. Some figures which he gives seem to support this view, but nothing definite has yet been proved, and the sex of such flies as have been taken at unusual distances from water has been recorded in too few instances at present to be of any decided value though, so far, they seem to have been more often females.
I do not propose to relate here the deplorable ravages of sleeping sickness which have been recorded in their reports of certain localities by those medical officers who have examined the most highly-infected districts. The state of things existing in such places has already been sufficiently well described for the situation to be well understood, it is not materially altered with regard to them, nor do I think it is under-estimated at present, either in existing accounts or in the general impression which prevails among the public. I will only state here that, however great the past ravages and however high the existing percentage of infection' (and in some of the worst localities I fear this is very high) recent investigations show areas, those areas in which the disease is communicable to that the "infective man, are much more circumscribed than was supposed, while the "safe" or fly- free area in the Protectorate is very much more extensive than at one time it was dared to hope.
These are facts which are not only reassuring in themselves as limiting the possible area of epidemic, but are also distinctly favourable to the successful application of preventive measures.
I decided that it was of no immediate importance to collate, as I at first intended, elaborate statistics of cases, death-rate, percentage of present infec- tion, &c., from the several districts which are being investigated. This would have been not only extremely difficult to carry out in the first instance among our native population, but would have involved a very great expenditure of time and labour which, I considered, could be for the time being more profitably employed, especially since no records exist of sufficient accuracy with which to make useful comparison, and I wished to concentrate our investigations at first on such points as might elicit or determine facts which appeared to be of more immediate practical value.
I saw, too, that if, as I had reason to hope and believe, the results of further investigation should favour the successful application of any form of segregation or deportation from infective areas, any such figures would, if collected, be rendered practically useless by the shifting of inhabitants entailed by such a measure. I consider that now, however, with our present knowledge, the time will soon arrive when such statistics must be collected. They should be as accurate as it is possible to make them, and should prove of the greatest value for comparing with similar figures which may be obtained later on, after the application of preventive or curative methods, or of both, for any given period. I should propose that they bo taken only from one or two definite and not too extensive areas, which should be selected with regard to the reliability of the figures likely to be obtained in them, their existing conditions as regards sleeping-sickness and fly-distribution, and the facilities which they offer for being dealt with by preventive and curative measures.
Sufficient time has not yet elapsed for the medical officers to be able to report the effects of the local clearings which have been, or are being, carried out in their districts, but sufficient practical knowledge has been gained of the effects of clear- ing at Entebbe, Jinja and elsewhere, where some considerable time has elapsed since it was undertaken. Dr. Bagshawe, however, records the fact that the clearing of scrub for a space of about 100 yards by 50 yards on only one side of the ferry on the lower Mpanga River immediately banished all the flies, which were previously numerous, from the ferry itself, and this although all the large trees were left standing. This, no doubt, is a particularly favourable instance, and probably a success so marked would not be lasting in its completeness, but it nevertheless serves to show the immediate detrimental effect which clearing of foreshore or river-bank has on Glossina palpalis.
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Dr. Bagshawe has collected Glossina fusca in the country bordering on the north and east of Lake Kafuru (Albert Edward), and Dr. Densham has collected Glossina morsitans from the neighbourhood of Nimule and Glossina palpalis and morsitans from between there and Wadelai. The localities will be found marked on the accompanying map (No. 1.), and on another map, also attached, which I have compiled of the distribution of the several species of tsetse flies found in the Protectorate. (Maps No. II. and III.)
The general distribution of Glossina palpalis in the Uganda Protectorate will be best seen on the accompanying map, No. I., where it is recorded as accurately as is possible, and also that of sleeping-sickness, which, most intense in the infected fly-ranges, radiates or shades off from these and penetrates inland to a greater or less distance, according to the prevalence, intensity and reaction on one another, at the corresponding coast or river-side, of the various conditions which I have quoted above (on p. 14) from my former report as governing the spread of an epidemic (see Appendix E.).
I will now endeavour to deal with several points which remain to be explained or discussed in connection, chiefly, with the fly-range, which, it will be readily understood, is one of the most important factors to be considered in all measures of precaution or prevention used against sleeping-sickness.
I have already made use, above, of the term "natural range," and by this I mean the distance from the waterside (Note 2, p. 14) within which the flies naturally wander in their search of victims on whom to feed, as distinguished from the much greater distance to which they will follow victims who have come in contact with them by the fact of having passed through their "natural range" or feeding ground. It may not, at first sight, seem important to distinguish between these but, as a matter of fact, a distinction becomes most important, for example, in carrying out such a preventive measure as clearing, for, as we shall presently see, if the natural narrow range be constantly borne in mind in its application, the wide "following" range may practically be disregarded.
a
In order to be followed by a fly for long distances, such as have been mentioned above, a person must first come in contact with it in its natural range and, con- versely, a fly would never reach these long distances inland unless it had first found, within its natural range, a victim to follow. Let us take the case of a village the water-supply of which is from a stream or lake at a distance from it of 300 yards. The village itself may be (and practically always is) well outside the natural fly- range, but, if there are fly at the dipping-places, a certain number will follow far enough to reach the village more or less frequently, and thus this is brought within the "following" range. Yet, in order to protect this village from fly, there would be no necessity for clearing a width of 300 yards from the water-side, since a clear space of 50 yards, or perhaps even half that width, would banish the fly from the natural range, so that they could then no longer be brought from the dipping-places (or from any other bank or fore-shore which had been cleared to the village. Take, again, the natural range from any given fly-arca or feeding-ground, say, at a ford. If you clear this Ay-area, which is probably 20-30 yards wide, and so make it uninhabitable for the fly, or if you divert traffic from it to some fly-free ford near by, the corresponding "following" range, no matter how wide it has been, will now no longer exist, since persons crossing the cleared natural range or the new fly-free ford will no longer encounter flies which might follow them. In brief, therefore, in clearing or abolishing the natural range you also abolish the
following" range.
I have never myself seen Glossina palpalis more than half a mile from water, except where they were being brought in by natives, daily and in large numbers, for scientific purposes, and there was the possibility of occasional escapes. More- over, the few instances when I have seen it at this distance occurred at a station where the water-supply was half a mile away, and water was being constantly brought from a jungle-fringed, fly-infested shore. Those cases in which flies have been observed at considerable distances (from 300 yards to 2 miles) from any known water have, so far (apart from those reported as following" flies), occurred only in the most thickly jungle-covered districts, such as South Usoga and the Islands, and usually under abnormal conditions of rain and flood. In some instances their presence has been explained by the discovery of forest-streams or pools near by, and it is possible that such hidden waters may have been present in other cases, but a proportion remains in which apparently there is no such explanation. I think
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