In practice certain principles should not be lost sight of. Chief of these, are to prescribe as few remedies as possible, and to use no powerful drug without a very distinct idea of what it is intended to do. Whenever it is desirable to give a powerful remedy, in increasing doses until its physiological effects is produced, it should always be given by itself. Thus, it may be necessary to give arsenic, 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 may be summed up as follows:

1. To augment, correct, or modify the action

℞ Pulveris Ipecacuanhae.............................gr. xx. Divide into 10 powders. S. One thrice daily.

What is the nature of the case? Evidently a lesion of the mucous surface. Let us report a hypothetical case. The patient has a dry cough, is bilious, dyspeptic, has anorexia, tympanitis, and constipation, alternating with dysenteric discharges. He has some fever, or rather hot flashes with a hot dry skin. Urine scant and high colored. He is likewise annoyed with a dull headache, sleeps poorly and is easily fatigued, etc.

What therapeutical remedy is here required? An expectorant, laxative, alterative, diaphoretic, febrifuge, sedative and tonic. Any simple rem-edy having these medical properties, judiciously 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.

*Prof. H. C. Wood.

There are powerful medicines which act similarly upon some parts of the organism but dissimilarly upon other parts. By combining such remedies powerful 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, producing sleep, with the least possible disturbance of the heart and of the intestinal tract.

2. To obtain the joint action of two or more diverse remedies. Thus, in a cough mixture, morphine may be included to quiet the cough, while ipecac 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 understratum of bodily condition, which must be sought out and prescribed for simply.

3. 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 iodide of potassium in solution, corrosive sublimate is added, a new chemical compound is formed, which experience has shown to be of great value in syphilitic diseases. Griffith's anti-hectic mixture is another instance of the use of chemical changes, the proto carbonate of iron being formed out of the sulphate of the metal and the carbonate of potassium. In the famous Dover's powder no chemical change occurs, but the ordinary action of opium upon the skin is so enhanced that the combination may be looked upon almost as a new remedy.

4. 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 in selecting a substance free from medical properties, having no chemical incompatibility with the medical agent and of suitable physical character. Bread crumbs often make a good basis for pills, but with nitrate of silver they are chemically incompatible on account of the chlorides in them. When writing a prescription, the utmost care should be taken to use such excipients that the combination shall not only be attractive to the eye, but also as little repulsive to the palate as may be.*