. Animal parasites and human disease. Insects as carriers of disease; Medical parasitology. 242 THE TAPEWORMS They have been reported in a considerable number of other animals also but the cases are very doubtful. The fact that the larval stage can develop in man makes the species particularly dangerous on account of possibility of self-infection, either by contaminated hands or by a reversal of the peristaltic movements of the intestine which throws the ripe proglottids of the worm back into the stomach where the embryos in the eggs are liberated by the gastric juices. This is discussed furth
. Animal parasites and human disease. Insects as carriers of disease; Medical parasitology. 242 THE TAPEWORMS They have been reported in a considerable number of other animals also but the cases are very doubtful. The fact that the larval stage can develop in man makes the species particularly dangerous on account of possibility of self-infection, either by contaminated hands or by a reversal of the peristaltic movements of the intestine which throws the ripe proglottids of the worm back into the stomach where the embryos in the eggs are liberated by the gastric juices. This is discussed further on p. 251. The Dwarf Tapeworms. — The dwarf tapeworm, Hymenolepis nana (Fig. 90A), is_thc smallest tapeworm found in man, but it often occurs in such numbers as^to cause much irritation in the intestine. It is a common parasite in Italy, and occurs throughout the warm parts of Europe, Asia, Africa and America. It is probably much more common in the United States than is generally sup- posed, since it can easily be overlooked unless the faeces are microscopically examined for eggs. It is probably a common parasite of rats and mice as well as of man, though the rodent par- asite is believed by some parasitolo- Hi/mcnoiepis nana, X 7 (after gists to be a distinct species, UflcrkL?™"^^'"""""' ''^'''' Stiles considers the rodent parasite a sub-species, H. nana fraterna. The_adult worm^ which consists of from 100 to 200 proglottids, is usually little over an inch in length and less than one mm. (^ of an inch) in width. The scolex (Fig. 87G) has four tiny suckers and a crown of little hooks. The ripe proglottids (Fig. 84J) differ from those of the large tapeworms in being much wider than long, with the enlarged uterus in the form of a solid mass, partially divided into compartments instead of being branched. As regards life history, the dwarf tapeworm is commonly be- lieved to pass both its larval and adult stages in a single host, contrar
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectmedical, bookyear1918
