This disease of the pig is due to _Cysticercus cellulosæ_, the cystic form of the _Tænia solium_ or _Tænia armata_ of man. As a disease of the pig it has been recognised from the most ancient times, and is stated to be the cause of Moses and Mohammed having prohibited the consumption of pork by their disciples. In the Middle Ages it formed the subject of legislation. It was, however, only when the investigations of Van Beneden and Kuchenmeister had completed those of the zoologists of the seventeenth and eighteenth centuries that the evolution of tæniæ became well known and the importance of the cystic phase clearly established. [Illustration: $1] [Illustration: $1] =Causation.= The cause of cysticercus disease in the pig may be summed up in one phrase—viz., ingestion of eggs or embryos of _Tænia solium_. Young animals alone seem to contract the disease. After the age of eight to ten months they appear almost entirely proof against it. It is very rare in animals reared in confinement, but is relatively common in those roaming at liberty; because they are much more likely to discover human excrement and the embryos of tænia. The eggs having been swallowed, the six-hooked embryos are set at liberty in the intestine, perforate the tissues, enter the vessels, and are carried by the blood into all parts of the body. Those alone develop well which reach the interstitial and intermuscular connective tissue. The others in the viscera usually disappear. Their presence in the depths of the muscles produces slight general disturbance and signs of local irritation, due to the development of the cyst itself. At the end of a month the little vesicle is large enough to be visible to the naked eye; in forty to forty-five days it is as large as a mustard seed, and in two months as a grain of barley. Its commonest seats are the abdominal muscles, muscular portions of the diaphragm, the psoas, tongue, heart, the muscles of mastication, intercostal and cervical muscles, the adductors of the hind legs, and the pectorals. [Illustration: $1] =Symptoms.= The symptoms of invasion are so little marked as usually to pass undetected. Occasionally, when large quantities have been ingested, signs of enteritis may occur, but these are generally ascribed to some entirely different cause. In some cases there is difficulty in moving, and the grunt may be altered.