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PUBLIC RECORD OFFICE

C.O.

Reference :-

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PUBLIC RECORD OFFICE, LONDON

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of Entebbe or Jinja, was unnecessary as a sanitary measure, and, therefore, unde- sirable from an economic or practical viewpoint. The only practical experiment which could be devised would be one planned in conformity with actual condi- tions in the Bukakata or Entebbe Districts--in the Bukakata District preferably to Entebbe, because less expenditure would be required. Accordingly, an experi- ment was planned on these lines, but it was not approved, because official approval of it would have entailed official repudiation of the original premises upon which the suppressive and preventive measures had been based.

The most important part of these studies in the bionomics of tsetse-the experiment to confirm the accuracy and demonstrate the practical value and applicability of the knowledge acquired is, therefore, in abeyance, and must remain so until a decision is reached on the main point at issue. Until then it is impractical to proceed with further investigations (it is not even practicable to report in detail upon those already made), because there is no practical objective to work towards. According to the theory upon which earlier work was based extermination of fly was prerequisite to reclamation of infested territory. There- fore, as already stated, the knowledge required for application concerned the factors of which operate naturally, or which can be operated artificially, to restrict range the insect. But in practice it has been found unnecessary (up to the present time, at all events) to do more than to reduce density of fly in populated districts, or density of population in fly-infested districts, or, in one phrase, to reduce breadth of contact between fly and population to within moderate limits. If this is really sufficient, knowledge concerning factors which control range of the insect is more or less superfluous, whereas knowledge of factors which operate to control breadth of contact between fly and population--equivalent to frequency of contact between hungry flies and men-is specifically required.

Two very different lines of study are thus outlined. Which of them ought to be followed?

As a matter of fact, both were followed: the first up to 1915, and the second during the last months of field work. One of them was impractical, and the specific results of it are practically valueless, except as disjointed fragments of Which of in formation gained can be salvaged for use in the other connexions. these two lines of investigation ought to be reported upon?

In the accompanying manuscript neither has been reported upon, because this question has not been answered, nor any specific object for the preparation of any report defined. It contains a mere mass of unapplied, and, for the present, inapplicable, information of no practical value until a decision has been reached on the following points :-

(1) Shall the original plan for these investigations be followed, and an experiment be planned and conducted to test the accuracy and applicability of the conclusions reached?

(2) If so, shall the object be

(a) to exterminate fly and prevent all contact between fly and popula-

tion, in accordance with the theories held in 1906-07; or

(b) to reduce excessive density of fly and to prevent excessive breadth of contact between fly and population, in accordance with present practice as in the Bukakata District in 1915-16?

Unfortunately the decision cannot rest on the results of these studies in tsetse bionomics, which have only the most indirect bearing upon the point at issue. Every bit of information which seemed, even remotely, to bear upon them, and which could be gleaned from any available source, was included in a report pre- sented in 1916, upon which no action has been taken at this date of writing. The one phase of tsetse bionomics having any bearing on these points is the fly's choice of hosts and host preferences. This is enlarged upon in the accompanying manuscript.

Methods. The methods used in conducting these studies consisted in the main of what is termed in the following pages a fly survey" of the lake shore and islands. This survey was designed to measure as accurately as possible all pecu- liarities and variations in the range of the insect, and all variations in its density as they occurred from time to time in the same localities, or from one locality to another at the same time. Coincidently observations were made and notes kept concerning every factor known or suspected to operate in the "natural control" of range and density, with the object of identifying those of major importance, i.e., such

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as are responsible for easily measurable peculiarities in range or variations in

natural enemies density. No attempt was made to study specific factors-such as -unless they were indicated to be of sufficient importance to account for measurable variations in density. By this procedure much useless work was avoided.

Factors

These methods were especially applicable to studies having as their ultimate But after the readjustment or practical objective the extermination of the insect. of old ideas and preconceptions of the economic problem, made necessary by the discovery that it is practically unnecessary, and even, for economic reasons, unde- sirable, to undertake extermination of fy, entirely different methods of study were demanded. The questions to be answered involved less the range and density of tsetse and the factors controlling them than the injuriousness of the tsetse and the factors in its control. The injuriousness of the insect, or its injurious status in relation to a population occupying the same or adjoining territory, is, in part, but only in relatively small part, determined by density of infestation. of equal or even greater importance are those which control the frequency of con- tact between flies and persons, and these include the relative abundance of host animals (such as crocodiles), the principal occupations of the population, the precise location of points of occupation or concourse of the population with respect to colony centres of fly, and various others to which the original fly surveys had accorded only incidental attention or had left out of consideration entirely. Reduction in density of fly is one object; reduction in the injuriousness or injurious status of fly is, in actuality, a totally different object, and methods of study must vary accordingly.

Finally, it was disclosed that the question of paramount importance was one that required yet different methods of study. It is to define the extent to which frequency of contact between flies and persons inhabiting a given region must be reduced in order to bring human trypanosomiasis under effective and satisfactory control. It is a question which can only be answered by measuring the frequency of contact and the coincidence of trypanosome infection in the population. It is, I regret to say, impossible for me to carry on investigations along this most necessary line unaided. It is for the entomoligist to measure density of fly and frequency of contact between flies and men, and to identify and study the factors in control, but unless he is specifically trained to diagnose and detect trypanosome infection, his studies are incomplete and of relatively little value.

Every effort was made in 1915 to secure the co-operation of a Medical Officer for a tour along the coast and islands of Nyanza Province (British East Africa), where the riparian populations had not been removed: but, on account of the War, nothing could be done. Some little information on this point was gleaned from old (manuscript) reports of Medical Officers employed on "Sleeping Sickness extended Investigations" in Uganda, which, as far as it went, strongly confirmed the presumption that the disease is incapable of spreading unless there is exces- sive breadth of contact between fly and population-in excess, for example, of that encountered in the survey of the Buddu shore in the Bukakata District--and a few other scraps of information have been found in literature-for example, in Todd and Walbach's survey for human trypanosomiasis in the Gambia, which contains a few brief references to prevailing density of fly and frequency of contact-but it is a line of investigation which has yet to be systematically followed.

A BRIEF SUMMARY OF THE CONTENTS OF THE REPORT.

1. Disparity between the Sexes :—

(a) Experiment to determine if variations in sex ratio are due to differences in the purely local, or in the climatic or seasonal, conditions of life.

Diagram I.-The Konu-Damba group of Sesse Islands.

P

Table I. Catch of fly from Bulago and Tavu. Islands, showing relatively constant difference in sex ratio (such as can only be due to difference in the purely local conditions of life on the two islands).

Table II.-Showing extreme range in variation of sex ratio (observed) between

different islands in Victoria Nyanza.

Table II. (a).-Absolute extremes in sex ratio as encountered on islands and

mainland.

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