I need not suggest the importance, in the use of this class of medicines, possessed as they are of such diversified qualities, of selecting, on every occasion, the one best adapted to the particular demands of the case. it often happens that a complaint, which is benefited by one cathartic, might be materially injured by another. in their administration, moreover, it should be borne in mind that they may often be advantageously modified by combination. Very frequently two or more may be conjoined to meet coexisting indications. Thus, magnesia and sulphate of magnesia are often given together, when the object is at the same time to correct acidity, and procure the effects of a depletory and refrigerant cathartic. Calomel is administered with castor oil, to ensure at once an operation upon the liver, and a thorough evacuation of the bowels.

There is an important principle which regulates the combination of the more powerful and drastic cathartics, by which their irritant property is diminished, without impairing their purgative efficiency. The fact has long been familiar to the profession, and numerous combinations of the kind have been made from time to time. The explanation of this apparently singular result, which I have given since I first began to teach Materia Medica, is that, as the several cathartics operate on different parts of the alimentary canal, or on different tissues, and the irritant effect is diminished for each with the diminution of the dose, the conjoint irritation is little felt, because diluted and spread over a large extent, while the purgative effect must necessarily be the aggregate of that of the several ingredients of the compound. A degree of irritation which, concentrated within very narrow limits, might produce the most serious mischief, may be so weakened by extension as to become quite imperceptible. The compound cathartic pills of the U. S. Pharmacopoeia, of which more will be said hereafter, were formed upon this principle, and have been found to answer well in practice.

The purgative effect of the cathartics is thought to be increased by tonics, and especially the bitter tonics. Thus, it has long been admitted, that senna will act on the bowels in smaller doses, when associated with columbo, than when given alone. Bitters are often themselves cathartic in very large doses, and a part of their auxiliary effect, in the present case, may possibly be ascribed to that fact; but it is supposed, and as seems to me justly, that they are chiefly useful by the increased capacity of acting which they impart to the tissues. Nux vomica, which is an excellent tonic in small doses, is an admirable adjuvant of laxative cathartics, in atonic states of the bowels. it probably operates simply by giving due nervous tone to the relaxed tissue, so as to cause it to respond more readily to its peculiar stimulus.

Many cathartics are apt to cause griping pain, or nausea. These disagreeable effects may be in great measure counteracted by suitable measures. The object may be attained in two methods; first, by combining with the cathartic some substance which may so far alter its chemical nature as to obviate the griping or nauseating property; or, secondly, by administering other medicines, which may prevent or relieve these effects by their physiological action. Thus, in reference to the first method, senna, which is very much disposed to gripe, becomes comparatively mild, in this respect, when combined with one of the alkaline salts, as sulphate of magnesia, or tartrate of potassa; and the irritant properties sometimes exhibited by aloes are supposed to be ameliorated by the addition of soap. Examples of the second kind of qualifying influence are offered by the effects of the aromatics in obviating nausea and griping, when given with the cathartics. Nothing is more common than this association. It is the antiemetic and antispasmodic action of the aromatic which, in this case, counteracts the contrary operation of the purgative; and not any influence of the one medicine directly upon the condition of the other. On the same principle, carbonic acid water is an excellent vehicle for the saline cathartics, which it renders much more acceptable to the stomach, and less liable to be rejected in irritable states of that organ.

Cathartics should, as a general rule, be given upon an empty stomach. They not only act more rapidly in this way than when given on a full stomach, but also much more kindly, and with less irritation. They come into more easy and complete contact with the mucous membrane, and have neither the task of extricating themselves from the load of partially digested food, nor that of carrying it with them.

When the most speedy and most powerful effect is required from a certain dose, the medicine should be given in the morning, before breakfast, when the susceptibilities of the stomach and bowels have been recruited by rest. Very small doses of cathartics will often act efficiently, if given at this time.

If, on the contrary, it be desirable to operate as mildly, and with as little inconvenience to the patient as possible, and speedy action be not requisite, the cathartic should be given at bedtime. The susceptibility is diminished during sleep; and it not unfrequently happens that the medicine shows no disposition to act until the time of awaking in the morning; the patient having, in the mean time, been conscious of no nausea, pain, or other disagreeable effect.

Not unfrequently, opium or some one of its preparations, when indicated on other grounds, may be usefully added to a cathartic at bedtime. It generally secures a night's rest; and, when its restraining influence ceases in the morning, the cathartic will act very kindly.

During the operation of a brisk cathartic, or somewhat before it begins, the effect may be rendered more lenient, by the exhibition of some mild beverage, as barley-water, molasses and water, thin gruel, chicken-water, etc.

Hypercatharsis may be best counteracted by from five to fifteen drops of laudanum, or an equivalent quantity of some other preparation of opium, given by the mouth, or twice or three times the quantity adminvol. ii.-32 in the constipation of dyspepsia, there is generally an indication for something more than a mere laxative effect. The bowels usually participate in the inertness which gives character to the complaint; so that medicines somewhat tonic or stimulant, such as rhubarb and aloes, are generally preferable to the pure laxatives. But to the constipation of convalescence, and that of pregnant women they are peculiarly adapted; as well as to that attended with hemorrhoidal affection, or prolapsus ani. in the latter complaints, which are often aggravated if not produced by the hardness of the feculent masses evacuated, even though there may be a passage every day, the laxatives are indicated in consequence of their effect in loosening or softening the stools, without rendering them in the least irritant a. Laxatives Operating Physically.

Cathartics, in conformity with their degrees of activity, may be arranged in the three divisions of laxatives, purges, and drastic purges.