A review of the literature shows that isolation of protozoa from bacteria does not present any formidable difficulties. Such isolation has been accomplished by methods based on principles involving positive or negative geotropism of protozoa, migration of protozoa away from bacteria through semi-solid media, mechanical separation of protozoa and bacteria by micro-isolation, or the differential action of poisons on cysts of protozoa and certain non-spore-forming bacteria.
In cultivating isolated protozoa, provision must be made for a gradual adaptation to new conditions.
Physical and chemical considerations which must be taken into account to provide a favorable medium include isotonicity of the fluid part of the medium with those of the tracts parasitized by the protozoa, a balanced food supply and a balanced interaction of various respiratory factors, vitamins and catalysts.
The L.E.S. medium, providing both solid and liquid food, is probably the best for general use that has thus far been devised. Eutrichomastix colubrorum, Trichomonas foetus and T. Columbae, which may be considered as representative flagellate parasites of the digestive, urogenital and respiratory tracts, respectively, all find adequate nourishment in this medium in the absence of bacteria. However, for the growth of Endamoeba histolytica without bacteria the medium lacks certain essential factors, the discovery of which awaits future investigations.
Dr. Th. von Brand of the Catholic University of America and Dr. R. P. Hall of New York University have kindly read the manuscript and have offered helpful criticisms and suggestions.