It follows, from what has been said above, that we are to treat here as cholagogues only substances which are known to increase the secretion of bile, as measured by the augmented quantity of the coloured liquid evacuated, or by the deepened intensity of the colour. Some may be disposed to doubt the possession of this specific property by any medicine; and the number of medicines is certainly not great which are known to possess it; but, when it is considered that the administration of certain substances is uniformly, or almost uniformly, followed by bilious stools, no matter what may be the state of the system, whether in health or disease, and that this effect may be repeated as often as the dose of the medicine is repeated, showing that it is not dependent on the mere evacuation of the reserved bile of the gallbladder, we cannot reasonably deny the existence of such a class.

Like all other organs, the liver may be irritated to a point at which its function is diminished or suspended. if, in this condition of the organ, medicines are administered which abate, without entirely removing the' excitement, it may be reduced to that degree at which function is promoted, and the secretion of bile may thus be increased. Hence, when the liver is actively congested, and the biliary function checked, the administration of emetic substances in nauseating doses, or of arterial sedatives, may, on the principle referred to, prove Cholagogue. Thus, antimonials promote the hepatic secretion, when it is restrained by high vascular irritation or active congestion, as in bilious fevers, and the early stage of hepatic inflammation. Warm baths have the same effect by their relaxing operation.

Any excitant influence upon the portal circulation in the liver, which moderately increases it, may stimulate the secretory function, and produce an increased flow of bile. One of the influences of this kind is mechanical agitation of the liver, such, for example, as is experienced in horseback riding, and exercise in a jolting carriage, both of which act as Cholagogue agents in a torpid or inert state of the organ; but are, on the contrary, injurious, when the function is inoperative in consequence of an overwhelming active congestion.

Of a similar nature is the operation of emetics on the hepatic function. I do not here allude to the emulgent effect produced by their pressure. This has been already noticed. But the agitation of this very pressure excites the function, and thus often positively increases the secretion of bile. Hence the use of emetics in jaundice, dependent on the suspension of this secretion. An antimonial emetic is among the most effectual remedies in that disease:

Heat, too, is a powerful excitant of the hepatic function. There is an obvious reason why this should be so. When the system is heated above the normal standard, there is less of its superfluous carbon thrown off by the lungs in the shape of carbonic acid, because the heat generated by the oxidation of the carbon is not wanted. This element, therefore, which is noxious in excess, must seek some other outlet, by which it may .escape, without undergoing this kind of combustion in the body. Such an outlet it finds through the liver, by which it is thrown off in the shape of fatty matter or cholesterin; and, to accomplish this depuration, nature has established such a relation between heat and the liver, that the former is a powerful stimulant to the secretory function of the latter. The excitation produced by heat is often carried to excess; and hence the bilious diarrhoea, and the cholera morbus or vomiting and purging of bile, so common in hot weather. Not unfrequently the stimulation passes the secreting point, producing high vascular congestion or inflammation. Often, moreover, a steady continuance of the influence at the point of increased secretion, ends, after a time, in wearing out the excitability of the organ, and a torpid or inert condition of the function results. it is only, therefore, by a moderate and intermittent action that heat proves Cholagogue. Though more powerful as a cause of disorder in this way, than efficient as a remedy, it may nevertheless be used with advantage in stimulating the torpid liver, when the torpidity does not depend upon a previous pathological influence of heat itself. A hot bath may be used advantageously for this purpose. I have already stated that the warm bath may act as Cholagogue, by producing relaxation, in an opposite state of the organ, when the function is suppressed by over-excitement of the liver.

Another method by which the secretion of bile is promoted is by the contact of irritant substances with the mucous coat of the duodenum. Reference has been already made, more than once, to the sympathetic relation existing between a secreting gland and the surface of the cavity into which its outlet opens, as, for example, between the salivary glands and the inside of the mouth. Just as irritants, applied to the buccal mucous membrane, excite a flow of saliva, so may irritants of almost any kind, remaining for a sufficient length of time in contact with the inner surface of the duodenum, produce a flow of bile; and hence numerous bodies may occasionally prove Cholagogue, without any special influence over the function. Such, probably, are most of the drastic cathartics.

In relation to the special Cholagogue medicines, I have already treated of almost all which are known to belong to the class. it will be sufficient here simply to mention these, and to refer to the observations elsewhere made, for a particular account of their mode of action and therapeutic application in this respect.

The Mercurials are beyond all comparison the most powerful Cholagogue agents, and are much and very advantageously used in this capacity. (See vol. II. p. 264.) Of these calomel and the mercurial pill are most used; the former being much the more effective of the two. As stated on a former occasion, the mercurials are much more efficient in .this way when swallowed, than when applied externally; because, in the former method, they are absorbed into the portal veins, and distributed immediately to the secretory structure of the liver, along with the materials out of which the bile is made; while, by the latter, they reach the organ in much smaller proportion through the hepatic artery, which is probably intended to nourish the liver, rather than afford it matter for secretion.