See Dobell (1920), where these observations are considered in detail. * The discovery was reported by Virchow in i860. See Dobell (1919) for further details.f This discovery is usually incorrectly attributed to Lambl (i860). Cf. Dobell (1919 a, pp. 8-9, and 71 et seq. ) where additional details will be found.(2) The Phylum Mastigophora consists of all those Protozoa which move, in their fully developed and typical condition, by means of whip-like filaments or flagella-familiar to all who have studied Euglena, or any other common flagellate.(3) The Phylum SPOROZOA contains a number of exclusively parasitic forms, which in their motile stages-when present-move without the aid of any special external locomotory organs. The several common species of Monocystis, parasitic in earthworms, supply familiar examples-with their slow, worm-like motions, performed by the body as a whole.(4) The Phylum Ciliophora contains all the Protozoa which move, in their typical active stages, by the agency of many little hair-like threads or cilia -exemplified in the familiar Paramecium and other common ciliates.Each of these Phyla contains a vast array of species, variously collected into genera, families, orders, and higher groups. It will be unnecessary, however, to discuss their classification in detail here, and we shall limit ourselves to a consideration of the systematic position of those species alone with which the present work is concerned. It will suffice to note the general grouping of our forms, and their more obvious relations to one another.The human intestine harbours protozoa belonging to all the four Phyla just enumerated. As these groups contain organisms as different * See especially Yorke, Carter, Mackinnon, Matthews, and Smith (1917), Smith (1919, 1919a), Dobell (1921).tSee Dobell (1921). % Among more recent contributions to this subject the reader may be referred to the following : Galliard and Brumpt (1912), Paviot and Garin (1913), Landouzy and Debrd (1914), Bloch (1916) -French cases; Kuenen (1918) -Dutch cases; Fischer (1920) -German cases; Yakimoff (1917)-Russian cases; Kofoid, Kornhauser, and Plate (1919), Cort and McDonald (1919) -United States cases. There are also numerous other works dealing with the occurrence of intestinal protozoa in the inhabitants of temperate climates, but it would lead us too far to discuss-or even to attempt to citeall of them. See also the papers on French cases of Balantidiosis cited on p. 119 infra.* Numerous references will be found in the Tropical Diseases Bulletin. The reader interested in this subject may be referred to the following recent works, which will also supply him with numerous further references to the immense literature dealing with the incidence of intestinal protozoal infections :
