Page:Tropical Diseases.djvu/1008

950 Two groups of protozoal organisms of doubtful validity remain to be considered, the Spirochætes and the Chlamydozoa.

Regarding the systemic position of the Spirochætes a great deal of controversy has been waged during recent years (see p. 232). The group comprises a number of types, some of which are parasitic, others free-living forms, such as Spirochœta plicatilis and Cristispira balbiani of the oyster. Both possess a crest running the entire length of the body; this structure has been wrongly termed an " undulating membrane."

The pathogenic spirochætes are slender thread-like organisms containing chromatic material. Such are Sp. recurrentis (obermeieri), S. duttoni of relapsing fever, Sp. gallinarum of fowls, etc.; these species are transmitted by various kinds of ticks (Ornithodoros), bugs, and lice. In the case of S. duttoni the spirochætes apparently break up in the body of the tick into very minute forms, and then pass into the egg, and so to the next generation of nymphs (see p. 236).

For the spirochætes of syphilis and yaws the name Treponema was proposed by Schaudinn;* the parasites are termed respectively T. pallidum and T. pertenue.

A name proposed by v. Prowazek to include a number of doubtful organisms, as the name implies. These problematic bodies are so minute that they are said to pass through a bacterial filter. They are parasites of epiblastic cells, but according to some authorities they merely represent a nuclear degeneration. It is enough to mention that such diseases as vaccinia, variola, trachoma, epithelioma contagiosa of birds, verruga Peruana, measles, and foot-and-mouth disease of animals, have been ascribed to the agency of these Chlamydozoa.