In an article on this subject published in 1935 (1) the writer recorded that fecal smears made with water would bring out certain differential characteristics of the intestinal protozoa. Since then we have used this aqueous smear extensively and have found that for certain purposes it can be used advantageously in the routine fecal examinations for the intestinal protozoa and that it is particularly helpful to the student technicians and inexperienced workers.
We therefore desire at this time to present the aqueous smear as one of the routine laboratory procedures for the search and identification of the intestinal protozoa.
First of all, it should be understood that the trophozoites (vegetative forms) are killed and destroyed in the aqueous smear. This applies not only to the trophozoites of the amoebae but also to the flagellates and the ciliates. The process of destruction apparently is one of osmosis in which the ectoplasm acts as a dialysing membrane.