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Meanwhile, thousands of natives in this and other districts had died, and certain regions were practically depopulated. These did not include nearly all that were infested by fly and infected by disease. The lesson was severe, but the natives learned it, and by 1909 or 1910 a voluntary movement was under way-not so much from the infected to the non-infected regions as from the more dangerous to the safer localities in the infected zone.

By 1911 it was apparent that the disease was no longer spreading, and by 1912 that the population in the infected districts was actually increasing naturally in spite of continued mortality. Figures indicative of this were presented by the Provincial Commisioner in his annual report, and, while complete figures for later years are not immediately available, it is believed that this increase has continued. The natives moved back in numbers into the infected regions-even into those No restrictions or conditions have been which were practically depopulated.

imposed. Precautionary measures have been urged, and men have been sent to see whether or not they have been carried out. Some clearing work has been done... how much I cannot say.

The disease is still causing many deaths, but if I interpret the situation the natives are now thoroughly conversant with the cause, and every death which occurs natural balance" of a sort A serves to emphasize the need of continued caution. has thus been struck between the human and its parasitic organism, which appears to be quite stable, i.e., a recurrence of epidemic appears to be unlikely because continued heavy, but not excessive, mortality has inspired caution rather than fear.

As is natural, the birth-rate amongst the depleted population has risen: so much so that it has, possibly, not only offset the unusual mortality, but so that the actual rate of increase in population is greater in the infected than in the non- infected districts. (The Kavirondo population, unlike the Baganda, is increasing steadily and rapidly.)

59. It would thus appear:

(1) That a native population can exist, and, apparently, increase in an

infected and fly-infested region.

(2) That the native to the region much prefers taking the risk, even after he has learned to estimate and appreciate it, and to realize that escape from it is possible.

54. It also appears that that which has come about in East Africa also came about in Bunyoro, where, it is understood, numerous endemic centres of the disease were exposed by the subsidence of the epidemic which had raged prior to 1906. These were largely done away with by depopulation measures which went into effect in 1909 or 1910, but similar endemic centres are believed to have persisted to this day at points on the Nile and in the Mpologoma region in the Eastern Province, and it is as certain as any statement of the sort can be that on the lake shore and islands of Buganda the same conditions would eventually have come into being had nothing been done. As is pointed out by Dr. Hodges, in a document quoted elsewhere, the natives would have come in the course of time to realize that none incur special risk saving those who through ignorance, or deliberately, expose themselves to it. Once this knowledge becomes general ignorance ceases to be a factor favouring epidemic.

55. And, I think, we ought to give the native credit for an instinctive know- The decreasing number of deaths ledge of what is good for him in the long run. per thousand inhabitants per year must have impressed itself upon the peoples of Buvuma and Sesse, as well as the fact that they had been the unfortunate victims of an unforeseen and terrible calamity. The worst must have appeared to be over (as following the climax of an epidemic of smallpox, etc.), and, with each But for the respect year that passed, better conditions to be coming about. accorded by their more intelligent chiefs to the opinions of Europeans, who either told them or allowed them to believe that unless they left their country all would die, they would certainly have remained, and, in time, have learned, as did the With the Kavirondo, which amongst their villages and islands were the safer. death of the enormous number of victims which had contracted infection during the rise and height of the epidemic, danger of contracting infection would soon have been reduced to a minimum, increasing only with the increase of population and the reoccupation of dangerously located villages, plantations, or fishing grounds. The attitude of the native who takes risks of infection, but who stays at home and continues his fishing, is hardly stranger than that of the European

who risks infection by strange diseases in the hope of bettering his fortunes in tropical Africa.

56. In the light of later events the native's attitude can hardly be said to have added much of gravity to the situation.

(F)—Conditions favouring Transmission of the Disease.

(See excerpt, paragraphs 23 and 27.)

57. If put into syllogistic form the argument put forward in these para- graphs appears to be as follows (the italics are mine) :-

"The tsetse fly is an indispensable link in the chain of infection."

The presence of even a single infected person in a locality infested by the tsetse flies may entail the infection of the whole community."

"We should, consequently, either remove all the tsetse flies from infected areas or else withdraw all infected persons from fly-infected regions." 58. There is, I think, a fallacy in this argument, for although the conclusion is perfectly logical that, by carrying out either of the measures mentioned, further infection becomes impossible, it by no means follows that the removal of all flies or of all infected persons is necessary or necessarily desirable. It merely points out one way of preventing spread of disease, whereas, by the terms of the syllogism, an indefinite number of others may exist.

59. It is well to recall, in this connexion, that Glossina palpalis is not an indispensable link in the chain of infection, except in so far as it is or appears to be an indispensable factor in natural epidemic. There are plenty of chances for the disease being transmitted in other ways-but they occur so very rarely in nature that they can afford to be, and are, ignored. When tsetse is present the chances favouring transmission are notably increased, but it remains just as much a question of chance as ever. A fly capable of becoming infective (and many appear not to be) must feed upon an infected animal (man or any other) capable (at that moment) of infecting it, and (at a certain time) afterward it must feed upon another animal (man or another) capable of becoming infected. It happens that flies feed most freely on animals incapable of transmitting or of receiving infection, and it also appears that many animals which can transmit infection, and are infected, are actually capable of transmitting it during certain periods only. There are really a great many chances against transmission taking place, and a rather elaborate combination of circumstances is necessary to ensure it. And it is no less an indispensable factor in nature, that such combination of circumstances should come about at least once within the time limit set by the length of life of each infected animal in turn.

60. To take the example of a single infected person coming to live in a fly- infested region, the chances must turn up in favour of the act of transmission taking place at least once during the remainder of his term of life or else infec- tion dies with him. If they turn up once, and once only, they must turn up again during the period which the second victim lives, or infection dies. It might be considered that the chances were even for or against the act of transmission taking place the second or third time under such conditions.

61.

If the chances favour the act of transmission taking place two times during the life of the new comer they would be about evenly in favour of the two new victims infecting four others, and so on, and an epidemic would soon be fairly under way and would continue to increase in severity until conditions unfavourable to transmission supervened (as eventually they must).

62. Thus, on Sesse, in 1909, it can be stated with assurance that the chances did not favour transmission taking place once, on the average, during the time limit set by the average length of life of the infected persons, so that with every day that brought the death of cach nearer the danger of infection spreading became steadily less, and the epidemic must have declined to the point of dis- appearing unless conditions more favourable to transmission were to have super- vened in turn (as eventually would pretty certainly have happened).

63. If, now, the various tables prepared to show the course of the epidemic in the several sazas are referred to. it will be seen that it spread from one to another. westward from Busoga and Buvuma to Sesse. and through Chagwe and Kvadondo to Mawakota and Buddu; and that it reached its climax on different years in different sazas. Also, following its climax. that it began to decline,

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