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XII] thickness, some being twice the diameter of others ——facts suggesting a longitudinal, that is protozoal, rather than a transverse or bacterial method of division; (d) the parasite keeps alive for many days—— forty—— in the body of the bug; (e) at least in the case of the African form, it enters the egg of the tick in utero; (f) it is communicated by an arthropod. Schaudinn propounded the view that the leucocytozoon of the owl (L. ziemanni), after fertilization in the gut of the mosquito, gave rise to an enormous number of trypanosome-like forms which he regarded as spirochætes. .These he considered were a flagellated stage of an intracellular organism and, therefore, belonged to the protozoa. He stated that he had compared his mosquito-bred flagellates with S. recurrentis and S. anserinum, and that he found they agreed completely in morphological character with what he considered the spirochæta stage of L. ziemanni. Before his death Schaudinn seems to have modified his opinion, for in a later paper he states that L. ziemanni is far removed from the typical spirochætes such as S. recurrentis. Novy and Knapp claim that their observations on the cultivation of trypanosomes in the blood of birds ——which, so far as microscopical examination went, appeared to be free from these organisms—— show that Schaudinn, probably unconsciously, worked with mixed infections; and that the trypanosomes which he regarded as a stage in the life of the intracellular L. ziemanni were not in any way related to the spirochætes, but merely a trypanosome derived either from birds or from trypanosomes of the mosquito, which is itself very liable to this type of infection. This question of the place in the natural kingdom of the spirochætes of relapsing fever is still undecided. The trend of some recent investigations is to relegate them to the bacteria. Dobell,* as the outcome of improved technique, holds that the argument founded on longitudinal division for regarding them as protozoa is based on imperfect observation; and that the argument based on hereditary transmission