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Table of Apothecaries' or Wine Measure.
Table of British Imperial or Pharmacopeial Measure.
The Metric, or Decimal System of Weights and Measures, is generally used on the continent of Europe, and also by French and German physicians in the United States. Its three standard units are the following, viz. :—
A Meter, the standard unit of linear measure and also of the whole system, is the tenmillionth part of the quadrant of the earth, i. e., the forty millionth part of the earth's circumference around the poles. One-tenth of the meter is the Decimeter, one-hundredth is the Centimeter, and one-thousandth is the Millimeter.
A Liter, the unit of measure of capacity, is the cube of a decimeter. One-thousandth of a liter is the Cubic Centimeter, which measure of pure water at its maximum density weighs one Gramme.
A Gramme, the unit of weight, is the weight of the one-thousandth part of a liter of water at its maximum density. Its tenth is the Decigramme, its hundredth is the Centigramme, and its thousandth part is the Milligramme.
The metric measures above noted are those used chiefly in pharmaceutical practice, but the system embraces many other terms of increase which are set forth in the following table :
I gramme =
.001 Cubic Centimeter.
The relations between the Metric Weights and Measures and the Apothecaries' are as follows, viz. :—
= 0.0161613 cubic centimeter.
.1 Decigramme. .OI Centigramme. .001 Milligramme.
The Metric System is making way but slowly in this country although its progress is aided by every process of forcing which scientific bodies can bring into action, and it remains to be seen how much its adoption in the last edition of the U. S. Pharmacopoeia will influence the medical profession in its favor.
With all the influence brought to bear in its favor it certainly has not yet been adopted by any considerable proportion of native-born and home-educated physicians and pharmaceutists. Its chief disadvantage is one which is inherent to any decimal system, viz.-that the number ten cannot be divided more than once without producing a fraction. This is partly compensated for by the practice of dividing five into the three parts of 2, 2 and 1, and on this principle metric weights are usually constructed. In writing or reading prescriptions it is sufficiently accurate to consider a gramme as equivalent to 15 Troy grains, and a cubic centimeter (milliliter) as equivalent to 15 minims, or one-fourth of a fluidrachm. All other terms, units or prefixes belonging to the metric system may be wholly ignored by the physician and the pharmacist. The decimal point after the gramme or the cubic centimeter should always be replaced by a line, so as to avoid errors which in many cases might prove serious, from the misplacement of a point, the dropping of a spot of ink or the intrusion of a fly-speck. The simplest method of writing a metric prescription for one not practiced in the system is to first write for one dose of the medicine in grains and minims, then by substituting the same number of grammes and cubic centimeters (fluidgrammes) we get fifteen doses in metric terms. Of course, when a mixture or solution is desired the proper quantity of vehicle must be added to give the dosage in such measures as may be deemed convenient for administration. For example:
B. Quinine Sulphatis,
. gr. j,
gr. or 0.016,
Massa Ferri Carb., .
One dose. gr. j, gr. ij, gr.
Ft. pil. No. xv. Sig.-One pill thrice daily after meals.
This gives a two-ounce mixture approximately, of which the dose would be “a teaspoonful thrice daily."
15 doses metric.
The above rule will answer for all liquids except those which are very heavy (as Syrups and Chloroform), or very light (as Ether). Measures may be entirely discarded, and all fluid quantities expressed in grammes. The average drop of water may be considered equivalent to 0.05 cubic centimeter (or gramme), the average teaspoonful to 5 c. c., the tablespoon
ful to 20 c. c., the Troy 3 to 30 grammes, the fluidounce to 30 c. c., and 8 fluidounces 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:
Tinctures. (Grammes.) 28.00
Syrupus Acaciæ, 44.
236.16 A table of equivalents between Apothecaries' and Metric Weights and Measures will be found in the Appendix.
Tinctura Aconiti, 146.
Liquor Potassæ, 62.
Liquor Hydrargyri Nitrat., 131.
Vinum Opii, 100.
Tinct. Opii Deodorat., 110.
Tinct. lodi, 148.
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 4 teaspoonfuls or fass, while the wineglass is supposed to contain about fij. 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.]
Ether. (Grammes.) 22.14
Oleum Ricini, 77.
Ext. Hyoscyami Fluid., 160.
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. 1 = sp. vol. and therefore sp. gr. X sp. vol. = I.
[A table of the specific gravity and specific volume of several liquids will be found in the Appendix.]
Extemporaneous Prescriptions are formulæ 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 ingredient 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.
Basis, or chief, active ingredient.
Adjuvant,-to assist the action of the basis.
Corrective, to correct some injurious quality of the other ingredients.
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 corrective 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 comprehensive, and at the same time serve to indicate the style of abbreviation usually employed. The following formula is that of the Pharmacopoeia for the Compound Infusion of Senna, or the old-time "Black Draught,' except that approximate weights and measures are substituted for the pharmacopoeial parts:
July 6th, 1886. SUPERSCRIPTION.
For Mrs. Steele. Recipe, Take,
Of Senna, half an ounce;
Of Fennel, one drachm;
Of Boiling Water, eight fluid ounces.
Signa, Mark, or Write thus-A wineglassful every four hours till it
T. F. Wood, M. D.
Abbreviated in the style usual with physicians the above prescription would read as follows, viz. :—