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234 through the tick is equally inapplicable, seeing that we now know that a bacterium, B. cuenoti, is hereditarily transmitted by passing into the germ cell of the cockroach. Moreover, Noguchi has succeeded in cultivating two strains of pathogenic spirochætes—S. duttoni and S. obermeieri.

Cultivation.—The successful cultivation of this as of other spirochætes has been performed by Noguchi, and more recently with simplified technique by Hata. For information as to the method, see p. 655. According to Noguchi the organisms multiply by longitudinal division in artificial culture.

Different species, or strains, of relapsing-fever parasites.—Having had the opportunity of examining the blood of a patient from Gibraltar suffering from her eighth paroxysm of relapsing fever, I suggested, on the

Fig. 61.—Spirochæta duttoni.

ground of the unusually large number of relapses and the locality in which the infection was acquired, that there might be several forms of this type of disease, due to different species or varieties of spirochætes. In 1905, in the discussion following the reading of Dutton and Todd's paper on tick fever (Brit. Med. Assn., 1905), Sambon made a similar suggestion, basing it on the wide geographical distribution of relapsing fever, the apparent clinical differences of the disease in different places, and the diversity of animals believed to transmit the infection. Koch pointed out that in African tick fever the febrile stages are shorter (under three days) than in European relapsing fever, and that the spirochætes in the blood are comparatively scanty; similar observations have been made by Philip Ross and Dutton and Todd. Novy and Knapp, in comparing specimens of spirochætes from European and