In writing a prescription we assume that it is intended, as should always be the case, to fulfil a single therapeutic purpose only; and we are to decide first, whether the medicine shall be administered in a solid or in a liquid form; and second, whether a single remedy or a combination of remedies shall be prescribed.

The tendency to-day, among many able therapeutists and clinicians, is to prescribe single drugs or simple combinations, while the prescriptions of former times containing a large number of ingredients, the so-called "shot-gun" prescriptions, are good examples of polypharmacy. There is, however, danger in going to the extreme of sacrificing therapeutic efficiency to simplicity of form and elegant pharmacy; and it must be confessed that such compounds as Warburg's tincture and the bolus prescribed by Dr. Graves in the treatment of dropsical patients prove the efficacy of polypharmacy in many cases.

As a general rule, we prescribe only one drug to provoke emesis, and a combination of several if we wish a diuretic. A purgative is usually multiple, but if the selection be castor oil or croton oil, it will be single.

After we have selected the basis, or chief ingredient or ingredients, of our prescription, the next point to determine is whether we can add anything which will in any manner be of real assistance to that basis. This ingredient, or adjuvant - as it is called - has usually a physiological action similar to that produced by the basis, as in combining two cathartics or two diuretics to act upon different portions of the intestines or kidneys. Sometimes, however, an adjuvant may differ in its effects - as sulphuric acid serves as an adjuvant to quinine by favoring its absorption and thereby hastening and increasing its action, as mercury assists the action of squills upon the kidneys, or as iron is an adjuvant to a cardiac stimulant.

Having chosen the adjuvant, the next point to consider is whether the action of the drugs selected may not be rendered more kindly through the addition of some other substance as a corrective - that is, to correct some disagreeable effect of the active agents. For example, extract of belladonna or hyoscyamus relieves the gripinccasioned by some of the more violent cathartics, like podophyllin. Other well-known instances of this kind are those of the aromatic spirit of ammonia, which mitigates the unpleasant symptoms of iodism, and hydrobromic acid, which lessens the untoward action of quinine.

Great care and thought should be given not only to the basis, adjuvant, and corrective, but also to the vehicle, which claims equal attention. The vehicle is the diluent, generally employed to make up the quantity to a definite number of easily measured doses. It may be a substance with a pleasant flavor or aroma, for a prescription is often rendered more palatable, and no less efficient, by some substance which produces a more agreeable taste. It is a mistaken idea that medicines, in order to be effective, should be repulsive to the patient. The homeopath's success is largely due to the very agreeable taste of his remedies. The mere caprice of the patient, however, should not be considered in the choice of a remedy, when, in the best judgment of the physician, it is indicated. Still, it is well to study carefully the art of prescribing agreeable doses, so far as may be compatible with fidelity to science. It is to be noted that pleasantness of taste is far more important in the case of fluids than in that of solids.

The favorite vehicles are: The aromatic waters, such as anise, cinnamon, peppermint, rose, etc.; the aromatic syrups, orange, orange flowers and tolu; the elixirs, fluidextract of licorice, etc. Some patients dislike sweet mixtures. In many cases simple syrup, glycerin or pure water serves, after all, as the best vehicle, although the physician's choice must be governed mainly by experience.

Other things being equal, a liquid is more rapidly absorbed than a solid preparation; but for exact dosage and convenience in carrying about, pills, capsules, tablets, and powders are favorite forms of administration. These should usually be given with plenty of water to aid disintegration, or to insure their solution or dilution. Many substances administered in pill, tablet, or capsule form will be very irritating to the stomach if given without water, or may fail to disintegrate so that they are passed in the stools unchanged. Tablets with strong irritating properties, like potassium iodide, potassium bromide, or ammonium chloride, should be dissolved in water before administration.

The bitter taste of a remedy may be avoided by administering the drug in capsules, or cachets, or as sugar-coated or gelatine-coated pills; or, if a liquid, by adding syrup of yerba santa or various aromatic or sweetened liquids.

Prof. H. C. Wood, M. D., has written so clearly upon the art of combining, or, more correctly speaking, associating, medicines that we cannot do better than quote his observations verbatim:

" The art of combining medicines is not a difficult one, but in practice certain principles should not be lost sight of. Chief of these are, to prescribe as few remedies as possible, and to use nowerful drug without a very distinct idea of what it is intended to do. Whenever it is desired to give a powerful remedy in increasing doses until its physiological effect is produced, it should always be given by itself. Thus, it may be necessary to give arsenic so as to impress the system, at the same time that iron is indicated; but the two remedies should be given separately, so that the dose of either can be increased or diminished independently of the other."

The principles of combination formulated below were long ago enunciated by Dr. Paris, but are to-day as imperative as ever. Medicines are combined:

"First. To augment, correct, or modify the action of a medicine. Thus, purgatives act much more kindly when a number of them are united together. The chief reason of this probably is that, as different remedies affect different portions of the gut, the whole intestine is best reached by a union of the diverse substances. It may take an intense irritation of the mucous membrane to purge as actively as does a mild irritation of both the mucous membrane and the muscular coat.

"There are powerful medicines which act similarly upon some parts of the organism, but dissimilarly upon other parts. By combining such powerful remedies effects can be obtained at the points where the two lines of action cross each other, without influencing to a great extent other portions of the system. Thus, chloral produces sleep by its action upon the brain, and also has a distinct influence upon the heart, but none upon the intestinal tract. Morphine acts upon the brain, and does not influence the heart, but has a powerful effect upon the intestinal tract. By combining chloral and morphine we get an overwhelming conjoined influence upon the brain in producing sleep, with the least possible disturbance of the heart and of the intestinal tract.

"Second. To obtain the joint action of two or more diverse remedies. Thus, in a cough-mixture, morphine may be included to quiet the cough, whilst ipecacuanha and squill (in accordance with the first principle) are added to affect the mucous membrane. The application of this principle requires caution, or the practitioner will be led into that chief abomination - polypharmacy. It is worse than futile to attempt to prescribe for every symptom. It is the underlying cause of the disorder, or the under-stratum of bodily condition, which must be sought out and prescribed for simply.

"Third. To obtain a special combination which is really a new remedy, or which experience has shown acts almost as a new remedy. Thus, when to potassium iodide in solution corrosive sublimate is added, a new chemical compound (potassio-mercuric iodide) is formed, which experience has shown to be of great value in syphilitic diseases. Griffith's antihectic mixture (mistura ferri comp.) is another instance of the use of chemical changes, the protocarbonate of iron (ferrous carbonate) being formed out of the sulphate of the metal and the potassium carbonate. In the famous Dover's powder no chemical change occurs, but the ordinary actiof opium upon the skin is so enhanced by the ipecac that the combination may be looked upon almost as a new remedy.

"Fourth. To afford a suitable form. Thus, acacia is added to make an emulsion, or confection of rose to make a pill. In the choice of excipients care should be exercised to select a substance free from medicinal properties, having no chemical incompatibility with the medicinal agent and of suitable physical character. Breadcrumb often makes a good excipient for pills, but with silver nitrate it is chemically incompatible, on account of the sodium chloride it contains.

"When writing a prescription the utmost care should be taken to use such excipients that the combination should not only be attractive to the eye, but also as little repulsive to the palate as may be. Whenever possible the pill form should be employed with bitter or disagreeable medicines. The pill may be readily coated with silver-foil; tonic pills may be coated with iron by shaking or rolling them in ferri pulvis while soft and sticky. Sugar-coated pills and 'compressed pills' are apt to get so hard and insoluble that their use requires caution. In regard to mixtures, flavoring oils should be freely used, and the power of glycerin to conceal the disagreeable taste of many substances should be remembered."l