During the past few years, the parasitic protozoa have received a great deal of attention, and now the list of diseases known to be caused by protozoa has become a long one. Through all of this, the question has frequently been raised whether the protozoa found in certain diseases were really the cause of the disease or whether they were harmless parasites, their finding being purely coincidental.
And nowhere has the question of pathogenicity or non-pathogenicity been raised more frequently than in connection with the parasitic protozoa in the intestine of man. Thus, very recently, one worker has studied the stools and the intestinal lesions in a series of cases of amebic dysentery, and on the basis of this study he maintains that amebas do not cause dysentery, but that their presence, even in the ulcers and in the tissues, is purely accidental. On the other hand, we have