Of the parasitic protozoa that infest the gastrointestinal tract, the flagellates merit more attention than is usually accorded them. American observers, who have interested themselves in gastro-intestinal parisitology, and particularly with the monocellular group of organisms, have attached little importance to this by no means uncommon group. English writers, too, have published scarcely any reports of intestinal diseases with which this class of organisms is associated. Continental clinicians, on the other hand, have been more active. Every now and then reports of cases of "intestinal catarrh," "protozoan diarrhea," and the like, find the flagellates playing a not inconsiderable rôle.
The flagellates come under the large group of Plasmodroma (Doeflein), and are of the class of Mastigophora (Diesing). We find the subclass of Flagellata (Bütschli) divided into two divisions of Monadina and the Isomastigoda. Of the former the cercomonas is the representative. The latter is divided further