TAPEWORM. An elongate flattened rib bon-like parasitic worm belonging to the class Cestoda (q.v.) of the phylum Plathelminthes. In the large majority of forms the body is divided tranversely by septa into links, seg ments or proglottids which are usually am spicuous externally although in a few less common genera such partitions are lacldng and there are rare species in which the body con sists of but a single joint or section.
The tapeworms are common in all verte brates and from their considerable size and length are the most conspicuous of all parasites. Three of the 24 species found in man are 10 meters or more in length and yet certain other species are so insignificant that they have long been overlooked. The large human tapeworms were lcnown to the Greelc and Egyptian phy sicians although all were regarded as of one kind and it was 1602 before the famous Basel clinician, Felix Plater, distinished two ldnds of tapeworms from man. The large bladder worins from various domestic animals were also well known to Greek writers on medicine but were considered as growths until Redi in Italy demonstrated their animal nature. They were, however, placed in a special class (Cystici) until about 1850 Kiichenmeister by feeding experiments established their relation as larval or immature forms of certain tape worms. The proscription placed by Moses on the use of certain flesh had its ground un questionably in the prevalence in such animals of bladder-worms. Hippocrates writes of the evacuation of pumpkin-seed-llice fragments as diagnostic of tapeworm and Aristotle showed that in contrast with round worms which are free the tapeworm is attached to the wall of the alimentary canal by means of its head.
The body of a tapeworm has at one end a bulbous enlargement known as the head or scolex which in other types has a different con struction but is oval with two elongate grooves in the fish tapeworm of man and more rounded with four cup-shaped suckers in the beef and pork tapewortns of man. (Cf. Figs 1 and 3). Following the scolex comes a very slender region, usually undivided; this is the peck. It changes very gradually into the Jointed body which becomes heavier and more conspicuously divided toward the large end where in the full grown intestinal parasites pro glottids are being regularly set free and evacu ated from the intestine of the host. Since the
body is highly muscular and has no hard skele ton, it varies constantly and conspicuously in shape, especially at and near the scoleic and neck so that the entire appearance of the an terior may be radically modified. (Fig. 1). The head may be armed with hooks as well as suckers, as in the human ihrasite often designated the pork tapeworm.
Most tapeworms are found in the intestine and in man this is the only normal location; the reports of their occurrence in the stomach being purely imaginary or due to reversal of the normal movement of the alimentary canal. They have been found in the bile duct and with the scolex embedded in the wall of the intes tine, but all such occurrences are rare and rank as abnormal. The effect of this parasite on the host is measured first by the loss of nutriment which must be relatively great .as the tapeworm is large and grows with striking rapidity. In the beef tapeworm the growth measures about 72 millimeters per diem which is equivalent to the formation of 13 to 14 proglottids daily. This factor is, however, inadequate to explain the results produced by the presence at times of only a single parasite. These symp toms are prominently of a reflex nervous character and are usually explained on the sup position that the tapeworms produce toxic substances which are absorbed by the host and induce a marked toxemia. One human tape worm produces a severe anaemia of the per nicious type recognized as characteristic of the presence of this species.
The symptoms of tapeworm disease are rather general and not well defined so that a in successive segments. The large bush-like masses are ovaries and the slender flattened structure near the posterior margin is the yolk gland. Between it and the ovaries lies the small spherical Mehlis gland formerly known as the shell gland, but incorrectly designated as such since investigations show that the material diagnosis must be made by the demonstration in the faces of loose proglottids which are discharged either singly or in groups of three or four. The abundance and distribution of tapeworms are not accurately known and statistical data exist only for a few localities and for selected groups such as hospital patients, inmates of public institutions and soldiers.