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which parasitise Musca domestica. It would be well worth while to make an effort to obtain a good supply of pups of all the species of Spalangia mentioned, and to endeavour to establish these parasites in a Glossina mursituns area, and watch the result. The Spalangia pupe could be conveyed in cold storage, in infected Hy-pups. The fact that both Musca domestica, Stomorys calcitrans, and more than one species of Lyperosia are found plentifully in parts of Tropical Africa infested by Glossina would seem to increase the possibility of establishing one or more species of Spalangia in these regions. For details of a method of artificially propagating Spalangia mucidarum, see H. Pinkus, The Life-History and Habits of Spalangia
cidarum, Richardson; a parasite of the Stable-Fly" (Psyche (Boston, U.S.A.), Vol. x., No. 5, Oct. 1913, pp. 148-158, 1 pl., 1 fig.): see also C. H. Richardson,
Studies on the Habits and Development of a Hymen- apterons Parasite, Spalangia muscidarum Richardson (Journal of Morphology (Philadelphia, U.S.A.), Vol. xxiv., No. 4, Dec. 20, 1913, pp. 813-549, 4 pl.j. For abstracts of both papers, see The Review of Applied Entomology, Series B., Vol. II., Part 2, Feb. 1914, pp. 22-24.
(viii) Food. A large series of G. morsitans caught where game is plentiful should be examined to determine the percentages which have fed respec tively on mammals, birds, and reptiles. Mr. Lloyd in Rhodesia examined 310 flies and found mammalian corpuscles in the gut of 70, and nucleated red corpus. cles, reptilian or avian, in the gut of 12, ie., in 15 per cent. of those which contained undigested blood. This is a considerable percentage, seeing that these flies are believed by many to depend on game for their subsis. tence. The examination should be repeated over a larger series, and an effort should be made to distin- guish, a Dr. Carpenter did, avian from reptilian blood.
Further, a large series of G. morsitans in an area free from game such as that described by Major Stevenson Hamilton (para. 1885) should be examined to determine on what food they subsist, and whether they contain trypanosomes pathogenic to laboratory animals or stock. This might be done in an "experi- area, if the flies remained ment-of-game-destruction
in it and no favourable opportunity occurred under natural conditions, but a naturally game-free area is preferable, because here the flies have had time to adapt themselves to their environment and possibly have learned to attacl animals which ordinarily they disregard.
Medica. Research.
(i) Reservoirs. (a) There are certain species of mammals which have not been examined at all or only insufficiently. Such, besides smaller mammals, are bush-pig, baboon, aardvark, hippopotamus. Attention should be directed to these creatures whenever they are found in fly areas. It is important that a sufficient number of young animals be examined, because old animals may have acquired immunity and rid them- Belves of the parasites.
(b) From evidence which came before the Committee it is possible that man himself may, under special conditions, be tolerant of T. rhodesiense and hence an A large series of apparently important reservoir. healthy young adult natives in an infected area should therefore be subjected to examination, their blood being scrutinised under the microscope, and inoculated There are difficulties in into susceptible animals. carrying out such examinations owing to the prejudices of the natives, but these could be overcome.
or
(c) Can birds harbour trypanosomes of man stock, and do they do so in nature? The importance of this investigation depends on the extent to which taetse feed on birds; this has not yet been satisfactorily ascertained for G. morsitane nor even for G. palpalis. Dr. Durham in London inoculated a kestrel (Falco tinnunculus) with rat's blood swarming with nagana. The blood of this bird was infective to rate 31 days later. He concluded that birds of prey might con- ceivably be reservoirs of infection.
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(d) A fresh test of the infectivity of the fly on the hors and islands of the Victoria Nyanza should be made (the last was in 1911), and more vigorous efforts should be exerted to prevent the clandestine visits of possibly infected natives to these places, for such visite may vitiate any conclusions drawn from the experiment.
(a) There is abundant evidence that native herda in certain parts of Central and West Africa are, like wild animals here and in other parts of Africa, tolerant of the presence of the trypanosomes which are continually injected into them by the local tsetse flies. Whereas domestic animals which are introduced rapidly sicken and die, the animals which have been long subject to infection take no harm. These animals, cattle, sheep, and goats, are easily handled, and their infection can be studied under natural conditions, but little attention has hitherto been paid to them. A study of their serum might lead to knowledge of the cause of their tolerance and enable us, by injections of serum or vaccines or otherwise, to produce a similar condition in introduced cattle, if immunitas sterilisans is not attainable.
(ii) Transmission Experiments.-Transmit T. gam- biense by G. morsitans and study carefully the infection produced in laboratory animals, with a view to the detection of a change in virulence or in the morphology of the trypanosomes. This experiment has been sug- gested by Professor Mesnil. It may be that with a chauge of invertebrate host there is a change in the biological character of a trypanosome. It is not yet certain that posterior nuclear forms may not be detected in T. gambiense infections even when trans- mitted by G. palpalis.
In transmission experiments with tsetse-flies and human trypanosomes it is not found possible to obtain a permanent infection in more than 5 to 10 per cent. of the flies. Miss Robertson, who has especially studied this problem, believes that the failure of the 90 to 95 per cent. to become infected is due to the tendency of the flies to digest their parasites. This problem is worth further study. It is possible that the small incidence of sleeping sickness in parts of Africa where the disease has been long established is due to the low percentage of flies which is capable of becoming infested rather It should be noted that than to immunity in man.
the few attempts which have been made to transmit T. gambiense by G. palpalie in West Africa have failed, and that all our data concerning transmission of this species by G. paipalis were obtained in regions where T. gambiense has only recently established itself, e.g., Uganda and German East Africa.
(iii) Action of Human Serum-Test in Africa the effect of healthy human serum on T. rhodesianse, both in vitro and in vivo. The recorded work has been mostly done in European laboratories. It is considered to be an important point of distinction between the two human trypanosomes that one is susceptible (like T. brucei), the other much less susceptible, to the action of hunian serumi,
The work in Africa is to some extent contra. dictory. Dr. Weck, in German East Africa (Rovuma), found that injection of human serum did not prevent the infection of monkeys with 7. rhodesiense. Dr Duke, on the other hand, found that when human serum was injected into a monkey infected with T. gambiense the trypanosomes disappeared from the circulation for a longer or shorter period. Probably rate or mice should be used in such experiments.
(iv) Diagnosis by Cultivation. There is doubt whether the method of diagnosing the presence of trypanosomes by keeping suspected blood in contact with artificial media, with a view to obtaining a multiplication of the parasites, has had a sufficient trial. There are difficulties in the field, but the method should have a further trial in places where there are well-equipped laboratories. The advantages of this method are obvious, the main disadvantage being that when more than one species of trypanosome may be present in the blood there is no means of telling which has developed in the culture; that is, the test serves for the diagnosis of trypanosomiasis, but not of the kind of trypanosomiasis. This, however, is of no
case of man. It may be pointed moment in the
that in kala-azar, 租 disease caused also out by a protozoal parasite, the cultivation method has been found of value, and that improvements in media have lately been introduced by the numerous workers who have cultivated malarial parasites.
(v) Racial Immunity.-Dr. Wade, who has studied Aleeping sickness in Ashanti, where he found two per thousand natives infected, concludes that most of the infected persons are strangers from the north, who are
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less resistant to infection than the indigenous natives. He believes that the disease would die out, or at least much diminish, if these north country ustives were to It would be worth while to cease to visit Ashanti. study carefully the racial history of natives found infected with T. rhodesiense in Rhodesia and Nyusa- land. It may be that those are the descendants of ustives who had not long been in contact with tsetse and hence had not developed meial immunity, as the mass of the natives may have done.