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756 drinking-water, and boiling, lysol, creolin, or creosol (1-10,000) for bathing- water. The free cercaria lives but a short time— at most forty-eight hours— in water, but a molluse once infected continues infective for months. The free cercariæ readily pass through the ordinary municipal filter-bed; they can traverse 30 inches of fine sand in five hours, but they perish, as has been stated, if they do not get access to an appropriate host within forty -eight hours. These facts should be taken into account by the sanitarian.

The occurrence of a schistosomum producing lateral-spined ova (Plate XIII. } Fig. 2) was noticed by Bilharzin 1851, but, believing the ova to represent peculiar capsules formed by the larvae after hatching, he confounded it with S. hœmatobium. After Bilharz several observers encountered female worms with lateral-spined ova in utero, and the idea of a dis- tinct species suggested itself to Sonsino and others, but this idea was at once discarded for other hypotheses. The lateral-spined ova being found only* in the fæces of Egyptian patients suffering from hæmaturia, the majority of physicians held that the peculiar position of the spine was due to distortion of the eggshell in passing through the muscular coat of the rectum, forgetting that oviposition takes place in the submucous layer, and that lateral-spined ova are found in the uterus of the parent worm. Sonsino suggested that the two kinds of eggs might represent respectively male and female embryos. Looss surmised that the lateral-spined ova might be the product of unfertilized females; but if the lateral-spined are merely unfertilized ova as he suggests, it is difficult to explain the presence of the species in America, where the lateral-spined ova are the only ones found.

In 1903, in examining a patient who had long resided in Antigua and other West India Islands