Let us consider the solitary worm of man (_Tænia solium_), it will enable us to understand all the others. Known by the name of tænia, or solitary worm, it is, like all the cestodes, a marvellous association of mothers and daughters, which are developed and vegetate in a 214 peaceable community. Each segment is a complete being, which encloses within itself an entire and very complicated apparatus for the fabrication of eggs. We give (Figs. 51 and 52) the representation of a solitary worm, peculiar to man, of the natural size; and at the side the scolex, usually called the head, slightly magnified. [Illustration: Fig. 51.--_Tænia solium_, or solitary worm; _a_, head, or scolex; _b_, tape formed of many individuals, the last of which, completely sexual, separate under the name of _proglottides_, and represent the adult and complete animal. Each solitary worm is a colony.] [Illustration: Fig. 52.--_a_, Rostellum; _b_, crown of hooks; _c_ _c_, suckers; 1, scolex of the tænia solium; 2, hooks expanded; _a_, heel of the hook.] Under its first vesicular form the solitary worm is planted in a 215 provisional soil. After this it is transplanted into a richer soil, where it flowers and throws out its numerous seeds. It comes to us from the flesh of the pig, in which there lived vesicular worms, of the size of a hazel-nut. The muscles are sometimes full of them, and the pig is then said to be "measly." The ancients noticed that the sucking-pig never takes this disease; and as _Sus scropha_ is the name of the pig, the term scrophula has the same origin as the specific name proposed by Linnæus. The measles in pork have been attributed to damp, to feeding on acorns, to hereditary causes, to contagion, even to injured corn and mouldy bread. All these theories we find in pathological treatises. The only true cause, however, is the introduction of the eggs of the _Tænia solium_ into the intestines. If we wish to prevent this infection, we must not permit the animal to eat man's excrements, nor to drink water in which substances that have become decomposed on a dung-heap have been allowed to remain.