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XII] African cases, noted that the spirochætes of the African disease are twice as long (16 μ) as the classical S. recurrentis, and, moreover, that the former has a tendency to dispose itself in figure-of-eight coils or in perfect circles. The Indian species 'they also incline to regard as distinct. The latter, like S. recurrentis, measures about 8 p, but is apparently thinner and more flexible, forming less regular spirals, which, moreover, vary in width. Like the spirochætes of African tick fever, the Indian variety has a tendency to form loops.

For the African form Novy and Knapp propose the name S. duttoni (Fig. 61); S. carteri would be an appropriate name for the Indian form. An Egyptian and an American spirochæte, named respectively S. berbera and S. novyi, have also been described. Such a nomenclature and differentiation can be regarded only as provisional: the evidence as yet is far too limited to warrant its permanent adoption; the recent elaborate experiments of Todd and Breinl have shown that the immunity conferred through infection with the spirochretes of Indian relapsing fever does not protect against the African form, and vice versa, thereby proving that, at least pathologically, they are distinct.

Mode of transmission.—— I have already referred to the Persian disease called miana fever, and to the carapata disease of the Zambesi valley, as forms of relapsing fever. They are certainly communicated by ticks, Argas persicus, or more probably, according to Balfour, by Ornithodoros savignyi in one case, Ornithodoros moubata in the other. Marchoux and Salimbeni were the first to show that a similar disease of fowls caused by the S. gallinarum is transmitted by a tick, the A. miniatus, which Neumann pronounces to be identical with, or a mere variety of, A. persicus. The relapsing fever of Europe has been supposed to be conveyed by the common bed bug, Acanthia lectularia; that of India by lice, possibly by mosquitoes, fleas, and bugs; that of Africa by ticks. Proof of transmission by the bug is by no means complete. Breinl, Kinghorn, and Todd,