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856 reintroduced per os or through a reverse peristalsis, because, as in Oxyuris vermicularis, the embryo will not hatch unless the egg be subjected to the action of the gastric juices. Young white rats proved most susceptible to the infection, whilst rats already harbouring the parasites were refractory. Grassi's observations do not entirely disprove the possible agency of an intermediary host as in other tapeworms, but they certainly show that it can be dispensed with, and indeed that as a rule the rat acts both as definitive and intermediary host. Experiments in man were not conclusive. Out of eight persons fed with eggs or mature segments of the parasite both from man and rats, only one became infected. This occurred, however, in a region (Catania) where many harbour this tapeworm. Pathogenesis.—H. nana is very minute, but as a rule it occurs in large numbers— usually hundreds, not infrequently thousands. When attached to the intestine it fixes its rostellum deeply into the lumen of a Lieberkiihn's follicle, thus altering and destroying many of the epithelial cells. It is obvious, therefore, that a number of these worms must give rise to considerable irritation and possibly favour secondary infection. According to Grassi, H. nana may bore deeply into the mucosa; and at the post-mortem of a case in which 400 specimens were found in the ileum, Visconti and Segré noticed that the mucosa throughout the small intestine was tumefied, hypersemic, and covered with a thick layer of greyish mucus, through which the worms were scattered. The most frequent symptoms reported by authors are abdominal pain, which may or may not be associated with diarrhœa; convulsions of various sorts,frequently epileptiform; headache and strabismus. The nervous phenomena are ascribed to the absorption of toxic products elaborated by the parasite. On account of its small size this parasite is easily overlooked. Diagnosis is based 011 the presence of the characteristic ova in the fæces. Some care is requisite in looking for the eggs, because, owing to their transparency, they may escape observation.

Treatment.—H. nana is readily expelled by male fern. If a patient harbours this parasite he should not be allowed to sleep in the same bed with another person. On prophylactic grounds, rats and