Barring a limited number of special workers, the conception of the whole of the medical profession is probably confused no more by any question than that of the intestinal protozoa. That when a physician receives a report of the presence of any of these organisms, all sorts of symptoms and conditions are attached to this fact, and it is made the basis of diagnosis and treatment of the sick, is a point of wide application. The particular importance of this fact lies in the likelihood of such a finding confusing the issue and leading away from some other existing condition. The recent war is responsible for exciting interest in, and spreading misinterpreted information about, intestinal protozoa. It stimulated the examination of feces to a much wider practice than existed before, and so intestinal protozoa are much more commonly encountered. One cannot even estimate the number of laboratory technicians who are