The treatment of any flagellate infection immediately brings up the question as to whether or not the flagellate to be treated is pathogenic to the host. Among the common intestinal flagellates found, we note the Trichomonas, Giardia, Chilomastix, Cercomonas and Waskia Intestinalis, in about the order named. Of these only the Giardia is more or less universally accepted as having definite pathogenic qualities.
The frequency of Trichomonas infections varies considerably, judging from the reports of various observers. Lynch found 20 per cent of his patients infected following a saline purge, Barlow reporting 25 per cent and Castellani about the same percentage. McNeil reported 5 per cent of patients from this clinic in 1917 harboring the flagellate but his examinations were not preceded by the usual purge. Kofoid and Swezy found only 0.1 per cent in 2400 cases of military patients from overseas and 0.5 per cent in 576 Home Service men.