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Microscopical examination of the fæces for ova of intestinal parasites.—If the fæces of the natives of warm climates, and of Europeans coming from warm climates, are systematically examined with the microscope, in a large proportion of cases they will be found to contain the ova of one or other of three species of nematode worms—Ascaris lumbricoides, Trichiuris trichiura (T. dispar), and Ankylostomum duodenale. The ova of tapeworm and of the common thread-worm (Oxyuris vermicularis) are



rarely found in the stools, as these parasites do not, as a rule, part with their ova until the joints of the former, or the entire body of the latter, have left the alimentary canal; but as the three nematodes first mentioned pass their eggs directly into the bowel, these eggs habitually appear in the fæces and constitute unequivocal evidence of the presence of their respective parental forms. Occasionally the ova of hepatic and intestinal parasites, such as Schistosomum japonicum, S. mansoni, Clonorchis sinensis, Fasciola hepatica, Fasciolopsis buski, and other rarer helminths, are encountered. Without large experience the ova of the rarer parasites cannot be identified off hand; but if the practitioner has learned to recognize those of the three common species, he will at one know when he comes across the ova of any of the rarer species, and, on referring to some special work on helminthology, will have little difficulty in arriving at a correct diagnosis.

The microscopical examination of fæces for ova, though somewhat disagreeable, is by no means a difficult matter. All 808