CO885-(18-19) — Page 1

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C.O.88

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(3) Indirectly by destroying their haunts and breeding-grounds, i.e., by clearing jungle and undergrowth, especially in the various fly- areas connected with places of human concourse or traffic. (4) Possibly by destroying or diminishing their food supply. C.-(1) Control or surveillance of travellers, traders, and emigrants from epidemic areas, and especially of their settlement or residence in or in contact with non-infected fly-ranges or potential epidemic

areas.

(2) Regulation and surveillance of camping places, transport-stations, &c., on traffic-routes by land and water, including effective clearing or diversion where these come in contact with fly-ranges. Before discussing the above I may perhaps mention that I have from the first been struck with the important bearing on preventive measures of the fact or accident of the relative immunity from sleeping sickness of Europeans and of certain of the better class of natives, and by the necessity for ascertaining on what conditions this immunity depends and how the protection which they afford can be extended, to any useful degree, to the ordinary native. It soon became evident that this apparent immunity depends on one main governing condition only, viz., exposure to the bite of Glossina palpalis, and on certain subsidiary ones such as clothing, customs, habits, occupations, dwellings, and especially the situation of dwellings, which determine the amount of such exposure.

I, therefore, drew attention, in May, 1904 (Note 3)* to this relative immunity of Europeans as pointing the direction in which was to be discerned the greatest hope for the native, and recommended, in connection with it, the systematic clearing of the usual places of human resort in infected areas and the removal of the sick to open spaces beyond the fly-range, as measures which would greatly diminish the risk of infection run by the majority of natives, especially the women and children, and would lessen the probability of the future occurrence of widespread epidemics.

After further investigations (Note 1) which showed, what I had already hoped might be the case, that the range of the fly from water was far narrower than had previously been supposed, at least in the region then examined and at the season in which the observations were made (these observations also pointing to the proba- bility that the breeding-grounds were always very close to the waterside) I again put forward the above measures as being the most practical and the most likely to produce satisfactory results, laying special stress on the importance and apparent feasibility by the natives themselves of "local segregation" of their sick beyond the bounds of the neighbouring fly-ranges.

I have now, after comparing the observations then made with the reports received in the course of the present investigations, come to the conclusion that some such measures as these are not only the most important which can be undertaken at the moment but that the time has arrived when their general application should be begun, since, as I have already stated, our knowledge is now sufficient for their practical use, and they seem, besides, not only to decrease in magnitude and difficulty with further investigation, but also to give, at the same time, greater hope of beneficial results. Moreover, I am convinced, for my own part, that the natives, if they were willing and would be guided, could apply both these measures, locally, to a sufficient extent to check the present epidemic, and to avoid future outbreaks of any magnitude without any great hardship or expense. I fear, however, that this will remain a possibility only, since their attitude is that of the negro generally, and they seem to expect to be paid by Government for any labour which they are recom- mended to undertake to save themselves from extermination. In some parts, especially in the Uganda Kingdom, the more intelligent will in time, perhaps very soon, appreciate the value of the advice that is now being given them, but it is doubtful if, even then, they will be inclined to carry it out for any useful period except under strong pressure.

Clearing and segregation, then, I place first of all the measures enumerated above, and the former, because it has already been applied locally and its utility proved, and because it also has an important bearing on many of the others, I will first discuss in detail.

• NOTE 3.-Islington Medical Society, May 17th, 1904; "Lancet," July 30th, 1904.

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In

No doubt this measure would occur, as an obvious method of extermination of Glossina palpalis, to any one who has been engaged in the study of sleeping sickness or has been especially interested in its prevention, but it is only of late that it has appeared to be either possible or worth while as a more or less general measure. order to apply it scientifically there is no doubt much that remains to be done by experiment and research to enable us to combine the amount and method which shall be at once the most effective and the most economical, but I hope to show, never- theless, that it should be applied as generally and as speedily as possible to all places in or in contact with infective areas the use of which is necessary for human resort, concourse or traffic.

At first the clearing of the forests and jungles for the purpose of exterminating Glossina palpalis, or even of appreciably diminishing its numbers, seemed a task too gigantic to be considered, except for a few special circumscribed localities. It was supposed that the whole of the vast forest and jungle-covered areas of the country, and even the immense swamps, might have to be dealt with in order to insure success. Further investigation has shown, however, that the haunts of Glossina palpalis, or fly-areas, are narrow and circumscribed, and their situations localised strictly by certain physical conditions; that their natural range from the waterside is limited, and probably never exceeds 50 yards, and that this, in the scientific application of clearing, is practically the only distance that need be considered, since the wider "following" range, which itself amounts to only a few hundred yards on the average, may almost be neglected.

More than this, it is extremely probable, though its larvæ have not yet been discovered (Note 4)* in natural conditions, that the breeding-places of Glossina palpalis are always close to the water's edge, and that a very narrow strip of clearing would suffice to destroy them as breeding-places.

-No doubt the general distribution of Glossina palpalis is governed by the presence or absence of suitable breeding-grounds, and its local range and numerical prevalence by the physical and climatic conditions prevailing at the breeding-grounds and by the opportunities for feeding. That these breeding-places must be very near to water seems practically certain, because the presence of the fly at any given spot is determined, chiefly at all events, not by the general facts of climate, but by the extremely local physical conditions which exist at the very margin of the water where it is found. It would even seem that the necessary conditions may vary more widely on the water than on the land side of the line of the water's edge. Hence it may prove that the strip of clearing which will be necessary on fly-infested banks and shores may be even narrower than the average fly-range, and it will have to be undertaken only on 'open" rivers and on shores free from wide swamp-belts (where, in fact, there is a certain amount of open water with contiguous shade, and with, in places, more or less defined banks for breeding-grounds), and may be limited chiefly to places of human concourse, where the fly is most liable to become infected. Morcover, as soon as we can recognise their limits with sufficient accuracy, it will probably be sufficient to attack the fly only or chiefly by destroying the breeding- places with their pupæ.

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But, even when the extent or distance of the breeding-grounds from water is accurately known, as it is hoped will be the case ere long, the exact width of clearing necessary on the average (for it is practically certain to vary somewhat in different localities) can only be determined by careful experiment.

Although vertebrates of various kinds have been artificially inoculated with Trypanosoma gambiense, yet, so far as is known at present, there is no wild or domestic animal which, itself almost or quite immune, carries this Trypanosoma so habitually as to act as a "reservoir" for the infection of sleeping sickness, as do the big game in the case of the Trypanosoma Brucei of Nagana. No animal, indeed, except the native dog,† and that in only a few instances, in places where the degree of local infection has been intense and the epidemic has been of considerable duration, has been found to be naturally infected; on this point, however, further research is much needed, for, if there be such a reservoir, it is most likely a domestic animal, and might possibly be the native dog itself; at any rate it is unlikely to be an animal which ranges, and would therefore carry the infection, very widely. It

• NOTE 4-See Appendix (B). Discovery by Dr. Bagshawe since the above was written. † Vide Appendix C. Professor Koch informs me that in the Serre Islands one monkey has been found, by one of his staff, to be naturally infected.

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