In some febrile and plethoric cases it is difficult to obtain the full action of a Purgative. This is because the absorption of the medicine is prevented by the pressure on the vascular system, and without this absorption the proper action of the Purgative cannot take place, for it has no opportunity of passing out of the blood through the glands of the bowels. In such instances it is well to combine the Cathartic with a small dose of Tartar Emetic or Ipecacuanha, which by its nauseant operation may diminish the vascular pressure, and thus favour the necessary absorption. The action of a Cathartic itself favours absorption, by draining away the fluid part of the blood, and so diminishing the tenseness of the vessels. ORD. IV. CHOLAGOQUES. Medicines which are thought to stimulate the action of the liver, and to promote the excretion of bile, are called Cholagogues. There is no doubt that the function of the liver, regarded simply as a gland, is of great importance in the animal economy. We know that certain matters are excreted from the system by that organ, which, when allowed to remain in the blood, as in the case of jaundice, are found to be hurtful. Also it appears that certain other parts of the bile are secreted or formed by the same gland, for the purpose of being re-absorbed into the blood from the intestine, and that they serve some useful purpose in the processes which go on in the circulation. (_Vide_ p. 137.) A disorder of the liver by itself, _i.e._ unassociated with diseases of other organs, is comparatively uncommon. A failure in the secretion of bile is evidenced more or less by the well known icteric symptoms. Jaundice is often caused by an obstruction in the hepatic ducts. In such cases it is worse than useless to urge the liver to an extra formation of a secretion which can find no outlet. But other cases, in which the discoloration of the skin is in general incomplete, may be due to torpidity, congestion, or chronic inflammation of the organ. In such instances Cholagogues may be cautiously used; but when there is acute inflammation they may do harm; and when there is a probability of structural change in the liver, they may be useless.