The explanation of the susceptibility of the third stomach in constitutional troubles has been sought in the source of its innervation. Electric stimulation of the vagus rouses the movements of the first and second stomachs, but not those of the third. Action of the third stomach is excited by stimulation of the spinal cord, and of the sympathetic nervous branches going to the ganglionic cells in the walls of the omasum (Colin and Ellenberger). Its nerve supply coming from a different source, derangement of its function may occur independently of antecedent disorder of the first or second, and its motor supply coming from a source so closely related to the vaso-motor centres, perhaps affords some explanation of the connection of disorders of the omasum with febrile and inflammatory diseases. Food is an important cause. Impaction of the omasum is a winter disease—the time of dry feeding. Dry, fibrous, innutritious fodder, and scarcity of water contribute to its production. It attacks cattle in spring or autumn on pastures in which fresh grass grows among the dead, dried, or withered stems of a previous growth. It occurs when stock are fed on corn or corn stalks (maize stalks) affected with smut or ergot, or on cereals or grasses similarly damaged, and in both cases especially when the water supply is deficient or restricted. Sheep and goats, which habitually drink little, suffer less than do cattle, which drink freely. =Other causes.= Fermented foods, microbian ferments and their products, which tend to induce torpidity of the omasum, fever, and lessened secretion of saliva, with diminished supply of liquid from mouth or rumen. Pericarditis, by causing vascular stasis in the omasum, may induce torpor and impaction. Lead poisoning paralyses action and favours impaction. Finely divided food stuffs—meal and bran—eaten greedily, may pass in quantity directly into the omasum and induce impaction. “The most acute and fatal forms occur in connection with a sudden change from dry to rich, luscious, green food in spring, the unwonted stimulus giving rise to general irritation of the whole gastric mucosa, with disordered and impaired function of all four stomachs, but especially of the third. Such cases are usually congestive and inflammatory, and the suspension of the gastric movements is a grand cause of impaction. In such cases, too, the brain or spinal cord, or both, are seriously involved, and the early death is preceded by torpor, paralysis, violent delirium or convulsions, following largely the type of acute lead poisoning.” (Law, _loc. cit._)