ful to 20 c.c., the Troy 3 to 30 grammes, the fluidounce to 30 c. c., and 8 fluid ounces to 250 c.c.

In prescribing Syrups or Chloroform, each Troy fluidounce should be reckoned at something more than 30 grammes-say 40; and if this be done, the difficulty of converting one scale into the other will be obviated. As to Syrups, Chloroform, etc., the following table shows the actual weight in grammes of each fluid ounce of the substances named :

A table of equivalents between Apothecaries' and Metric Weights and Measures will be found in the Appendix.

Approximate or Domestic Measures become necessary in apportioning doses for a patient, when liquid medicines are used. Of these the measure most commonly employed is the teaspoonful, which is generally taken as equivalent to a fluidrachm, though in most cases as now manufactured the teaspoon contains about 75 minims, or 25 per cent. more than the theoretical quantity. The dessertspoonful is about equal to 2 teaspoonfuls, and the tablespoonful to about four teaspoonfuls or f3ss, while the wineglass is supposed to contain about f3ij. The use of graduated medicine-glasses is strongly recommended instead of the above approximate measures. They may be obtained at a trifling cost in any well-stocked drug-store.

Drops (Guttæ) are very variable in size, though popularly supposed to equal minims, the variations in their relative dimensions being due to the viscidity of the liquid, the shape and surface of the orifice from which they escape, and sundry other circumstances. The Syrups and Mucilages produce large drops, while Bromine, Chloroform, and other heavy mobile liquids produce very small ones. These differences are well illustrated in the following table which gives the number of drops in a fluidrachm of several liquids of certain classes. [See the Appendix for a fuller table.]

Specific Gravity is the relative weight of equal bulks of different bodies. The specific gravity of water at a certain temperature (generally 59° F.) is taken as 1, and that of all other substances is expressed in terms of this unit. The Pharmacopoeia gives very complete tables of percentages. and specific gravities of Alcohol, Acetic, Hydrobromic, Hydrochloric, Nitric, Sulphuric and Phosphoric Acids, and of aqueous solutions of Potassa and Soda. The specific gravity of any substance is expressed by the quotient obtained by dividing the weight of a given measure of the substance by the weight of an equal measure of water. In pharmacy the specific gravity of solids is not of any importance, but that of liquids is a matter of constant value, and is determined in most cases by means of a specific gravity bottle or by a hydrometer, instruments which are described in any standard work on chemistry or physics. Modifications of the hydrometer with scales adapted to particular work are the urinometer, saccharometer, lactometer, etc.

Specific Volume is the relative bulks of equal weights of different bodies. In pharmacy it means the volume of the weight of a liquid compared with the volume of an equal weight of water at 59° F. The specific volume of a body is therefore inversely as its specific gravity, and is expressed by the quotient obtained by dividing unity by the specific gravity. =sp. vol., and therefore sp. gr. X sp. vol. = 1.

I

sp. gr.

[A table of the specific gravity and specific volume of several liquids will be found in the Appendix.]

PRESCRIPTIONS.

Extemporaneous Prescriptions are formula written by the physician on the instant (ex tempore) to meet the requirements of individual cases. A prescription should begin with the name of the person for whom it is designed, and the date on which it is written. Then follows the Latin word Recipe, usually abbreviated to the sign R, and signifying "Take," or "Take thou;" next the names and quantities of the ingredients to be used, which are also expressed in Latin; then the directions to the compounder, followed by the directions to the patient, the last being now usually expressed in English; and finally the signature of the prescriber.

A prescription then consists of four parts, viz.-the

SUPERSCRIPTION,-consisting of the name of the party, the date and the sign R.
INSCRIPTION,-the body of the prescription, which may consist of the-

Basis, or chief, active ingredient.

Adjuvant, to assist the action of the basis.

Corrective, to correct some injurious quality of the other ingredients.
Vehicle or Excipient,—giving it a suitable form.

SUBSCRIPTION,-the directions for the compounder, usually expressed in contracted Latin. SIGNATURE,—the instructions for the guidance of the one administering the medicine, in English, followed by the signature of the prescriber.

A prescription may however contain the base alone, or the base with the adjuvant, or the base with a simple vehicle or diluent, etc. A single ingredient may serve a double or treble office, as the Syrupus Rhei Aromaticus with Quinine, in which case the syrup serves as an adjuvant to increase the action of the quinine, as an excipient to cover the taste, and as a vehicle to facilitate the administration of the dose directed. The basis may not need any aid in doing its work, and may require no correc tive of its action nor any special vehicle. On the other hand there is no limit to the number of ingredients which may be used, provided the prescriber has a clear idea of something to be accomplished by each one, and also provided that there is no chemical or medicinal incompatibility between them. In olden times prescriptions were very complex, and contained a great many curious and incongruous ingredients. As Dr. Piffard well says, "the tendency of the present age is toward monorather than poly-pharmacy, and prescriptions with the orthodox adjuvans and corrigens are less frequently seen than formerly." There is danger however in carrying this simplicity too far, for there is no doubt but that proper combinations of medicines will often produce effects for the patient's good, which could not be obtained from the use of any one remedy.

An example will perhaps make the foregoing analysis more comprehensible, and at the same time serve to indicate the style of abbreviation usually employed. The following formula is that of the Pharmacopœia for the Compound Infusion of Senna, or the old-time "Black Draught," except that approximate weights and measures are substituted for the pharmacopoeial parts.

Signa, Mark, or Write thus-4 wineglassful every four hours till it operates.

SIGNATURE.

T. F. Wood, M.D.

Abbreviated in the style usual with physicians the above prescription

would read as follows, viz.

The above is given as an example of an ordinary compound prescription, but as the result is nearly identical with an official preparation, we might write the prescription simply as follows,—

R. Infusi Senna Compos. 3viij.

and this is the manner of prescribing the official compound preparations. It will be noticed that the term "basis" in the analysis of the formula covers two ingredients; but either of the two might be considered the principal agent, and the other one classed as an adjuvant.

As Pareira says, "These four parts of a formula are intended to accomplish the object of Asclepiades, curare cito, tute et jucunde; in other words to enable the basis to cure quickly, safely and pleasantly."

The Principles of Combination are so well laid down by Dr. H. C. Wood, that his words are appended verbatim, as follows,—

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 no powerful 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 phy-iological 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 dimin. ished 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. In the case of neurotics the principle has a very limited action, because so many of this class of remedies are physiologically more or less antagonistic; yet sometimes the principle can be advantageously applied: thus, the anesthesia of Chloroform or Ether may be prolonged by a hypodermic injection of Morphia; and Chloral and Morphia certainly make a mixture which is much more powerfully hypnotic than is either of the substances separately.

Second. To obtain the joint action of two or more diverse remedies. Thus, in a cough mixture Morphia 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 expe

rience 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 antihectic 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.

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 medical properties, having no chemical incompatibility with the medicinal 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 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 whilst 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.

In Writing an Extemporaneous Prescription, the first step is to put down the superscription, consisting of the name, date and the sign R. Next the name of each ingredient should be written in Latin and in the genitive case, each one on a separate line. Then the quantity of each article sufficient for one dose should be mentally determined and multiplied by the number of doses which the mixture is to contain, and the result set down in signs and Roman numerals. The directions to pharmacist and to patient being added, and the prescriber's name or initials affixed, the prescription is completed; but when very active agents are used, it is a good plan to go over the calculations a second time before letting it leave the hands of the person most responsible for its action. For pills or powders the same process should be employed, slightly varied according to the requirements of each case. Frequently the ingredients and quantities for but one pill, powder or suppository are named, with instructions to make a certain number after the formula. When an unusually large dose of any poisonous drug is prescribed, it is cus tomary to underline the quantity, so as to call the attention of the compounder to the fact that the prescriber is aware that the dose is above the average.

There is no royal road to prescription-writing; practice, care and knowledge of the whole subject is necessary to enable one to turn out habitually those elegant prescriptions which are properly termed "magistral," being the work of a magister, or master of his business. A fair knowledge of the Latin language is a sine qua non to every professional man, but especially to the physician. It is pitiable to see a Doctor write ignorantly of even the genitive case-endings of the drug-names which he

uses.

The teaching of Latin is not within the scope of this work, and