Page:Popular Science Monthly Volume 69.djvu/419

Rh the history of some Trypanosoma. At the present time, however, it appears much more likely that they are more nearly related to the hæmosporidia than to the flagellates, and Laveran and Mesnil's view assigning them to the genus Piroplasma, the same genus as the parasite of Texas fever, may be accepted.

Closely allied to Trypanosoma is the genus Spirochæta, a similar flagellate belonging to the order Monadida. In its general cork-screw shape it resembles Spirillum, one of the bacteria, but differs from this by reason of its plastic body and general mode of life. Many different species have been described, and considerable difference of opinion exists as to whether they should be classed as bacteria or as protozoa. One well-known form—Spirochæta obermeieri—has long been recognized as the cause of relapsing fever, and has been recently shown to be the cause of human tick fever in Africa, which is carried from man to man by the tick (Ornithodorus moubata). The organism of relapsing fever, however, does not seem to have a typical flagellate structure; there is unmistakable evidence of transverse rather than longitudinal division; its nucleus is distributed like that of a bacillus, and Novy has shown that it reacts like some bacteria during plasmolysis. The need of an intermediate host in the case of African tick fever seems to be the one distinctive protozoan characteristic.

While Spirochosta ooermeieri is perhaps a doubtful protozoon, there is less doubt in the case of other species, some of which have unquestioned flagellate characters, including typical nuclear structures, longitudinal division and the like, while in a number of species an undulating membrane analogous to that of a trypanosome can be made out. Some of the better known species are: Spirochæta dentium of the mouth; S. refringens of ulcerating tumors; S. gallinorum a blood parasite of fowls, and S. anodontæ, parasitic in the crystalline style of the mussel Anodonta mutabilis. A similar parasite, described first as S. balbiani, is found in the crystalline style of the oyster, but it has so many trypanosome characteristics that it is now called Trypanosoma balbiani. It serves to illustrate the close relationship between these two genera.

It is to this group of parasites that Spirochæta (Treponema) pallida, the cause of syphilis, belongs. The organism was discovered a year ago, and since that time has been submitted to the widest range of pathological research. A full life history has been published by Siedlecki and Krzyszakowicz, and some of the stages described by them are strikingly similar to those of Trypanosoma. Schaudinn regards it as sufficiently distinct from other Spirochæta species to justify a new generic name and calls it Treponema pallidum.