possible, the solid portion packed in a percolator, as before described, and the liquid poured on, until all has passed from the surface, when immediately a sufficient quantity of the original menstruum should be poured on to displace the absorbed liquid, until the required quantity has been obtained.

"Authority is given to employ, in the case of fluid extracts, where it may be applicable, the process of repercolation without change of the initial menstruum."1

Fractional percolation is the same process applied to two successive portions of the powder, the result being identical with repercolation.

Expression is the process of forcibly separating liquids from solids. It is a very ancient method, the best-known form being the wine- or fruitpress. After macerating a crude drug for the desired length of time, the full amount of tincture is obtained by decantation and expression.

Precipitation is the process of separating solid particles from a solution by the action of physical or chemical means. If the precipitate is of lower specific gravity than the liquid it will float upon its surface; if, as usually is the case, it is of higher specific gravity it will sink to the bottom of the receptacle. Precipitates may be curdy, granular, flocculent, gelatinous, crystalline, amorphous, etc. A magma is a thick, more or less tenacious, precipitate. Substances containing albumin are precipitated by heat; light precipitates silver salts; but the most frequent method of precipitation is by chemical action. This is resorted to (1) for the purpose of obtaining substances in the form of a powder, (2) as a means of purification, (3) for testing chemicals, and (4) to isolate chemicals. In assuming the crystalline form some salts take up considerable water, which is known as water of crystallization; the amount varies in different salts, but it is important to bear this in mind with some salts like sulphate of iron or alum, as the water should be expelled by heat before making them into pills or powders. Such salts are liable to deliquesce and become moist or liquid by absorbing more moisture from the air, or in a dry atmosphere they may effloresce from loss of water.

5. Pharmaceutical testing and analysis is the method followed in ascertaining the presence of certain constituents and determining the proportion. if present. The methods followed are not different from those employed in organic chemistry and in the laboratory. The pharmacopoeia supplies a list of standard reagents for the purpose of applying the tests prescribed in the text. As the processes of analysis are not peculiar to pharmacy, the space will not be taken here to consider them in detail. In practical pharmacy the microscope is indispensable for the recognition of drugs and adulterants and for the examination of crystalline deposits and sediments.

6. The preparation of extemporaneous formulæ is not different in principle from the official, except that some extemporaneous preparations may be ordered which have no relation to the pharmacopoeia. For instance, some preparations of the English, German, or other pharmacopoeias are occasionally prescribed, or formula which are original with the physician. Unofficial articles, or new remedies, are also often included in the magistral prescription, but care should be taken that this is not done to excess.

It

1 Pharmacopoeia of the United States of America, 7th Decennial Revision, p. xl et seq.

is by no means creditable to a physician to be constantly trying muchvaunted new remedies or proprietary preparations, and neglecting to use the older remedies of established reputation and of standard composition, which have received the sanction of the pharmacopoeia. The art of prescribing will now be taken up for consideration.

PRESCRIPTION-WRITING AND FORMULA.

In the progress of the science of medicine it has been found necessary, owing to the accumulation of knowledge, to institute special departments of study, as well as specialties in practice. It having become inexpedient for a physician to collect his own herbs in the fields, to make his own preparations, and to dispense his own prescriptions, these duties have been delegated and entrusted to the trained pharmacist and his assistants, who have special qualifications for the task, to which they devote their whole time and attention. This division of labor is to the advantage of scientific medicine, as the practitioner of medicine is relieved of routine work and has more leisure to devote to the study of pathology, diagnosis, and therapeutics.

The Prescription. The physician usually writes his directions, regarding the medicines which the patient is to take, according to a general form, the writing being called "the prescription" (præscribo, præscriptum, præscriptio, in Latin,-something written for, or ordered; in French, ordonnance). As a prescription furnishes very tangible evidence of the attainments of a physician, and, being preserved on the prescription-file of the pharmacist as a matter of record, may confront him in the courts of justice, it is of considerable importance that students should be well drilled in prescription-writing before graduating, so that they may be spared mortification and possibly the loss of reputation, caused by blunders or carelesslywritten formulæ, to say nothing of the risk to the patient.

The first point to be settled, in composing a prescription, is to determine the therapeutic indication and to decide upon the drug to be employed, and in what form it shall be given,-whether solid or liquid, and whether alone or combined with other remedies. Following this is the question of dosage and the number of doses and length of time during which the remedy is to be given, which determines the quantity to be ordered in the prescription. The body of the prescription, or the formula, may have the quantities written according to the metric system, but, as pharmacists and physicians are more familiar with apothecaries' weights and measures, it is better-for present purposes, at least-to follow the prevailing method, as a matter of precaution, and to prevent mistakes. It has been found that, by adopting a certain form in writing prescriptions, the work of compounding and dispensing is made easier and more certain, and the task of translation facilitated. In framing a prescription, certain principles should be kept in mind, in order that the product shall be creditable and accomplish the purpose for which it was written. The tendency of the day is toward simplicity, the elegant pharmaceutical preparations at our command having removed the necessity of the resort to polypharmacy, as it is called, when a large number of agents are combined in one prescription. As remedies

are modified in their action by association with others, it is often advantageous to make such a combination, and knowledge and experience are sometimes displayed to a marked advantage in originating such complex formulæ. Instances of this will be abundantly given in the section devoted to the consideration of drugs. It used to be the rule that a prescription should contain four parts,-(1) the base, (2) the adjuvant, (3) the corrigent, and (4) the vehicle; the dose of the first having been decided upon, the quantities of the other ingredients were made to correspond with it, so as to make the desired quantity of the medicine to be taken at a dose. The preparations of the pharmacopoeia, as a rule, may be prescribed without addition, except with water, or some other convenient diluent, when administered.

The first rule in prescribing should be to make a judicious selection of the active remedy or remedies to constitute the basis of the prescription, always taking a single remedy, unless a distinct advantage can be gained by using others in conjunction with it. In this connection, it should be noted that some drugs can be given in larger doses when thus combined, whereas others must have their doses reduced. As a general rule, where agents are from the same therapeutical class they mutually enhance each other's effects, and must be given in smaller doses than when given alone; when they belong to different classes, and especially when they act upon different organs, the dose can often be largely increased with advantage. Having settled upon the main remedy and its associate, and the quantity desired to be given, the question of eligibility comes up, in deciding upon the special pharmaceutical form to be employed. There are frequently representatives of the drug in question in several pharmaceutical classes,some in solid form, others liquid,-each having, or supposed to have, some special application or advantage in certain cases, and offering favorable opportunities for combination. It may be a matter of indifference which form or preparation of the remedy is chosen, but the probabilities are that it is not; and that some are better suited than others. Thus, some of the preparations of iron are astringent, others acid; others contain alcohol, or are combined with tonics and alteratives; one combination is especially diuretic, another is used as styptic, and rarely given internally; one is used only as an antidote for arsenical poisoning, and so on.

Having decided upon the principal therapeutic agent, if we conclude to give it alone, that will complete the prescription formula, and we have only to add the directions to the pharmacist and to the patient (the latter directions being simply what is desired to be copied upon the label of the medicine-bottle or package). If we wish to combine our remedies, the following objects may govern our selection: First, an addition may be made of some agent which will assist the action of the main ingredient, or two or more may be selected which mutually aid each other. This aid may be chemical in character, as where dilute sulphuric acid is added to quinine sulphate to help in its solution, or hydrochloric acid is added to a digestive mixture containing pepsin; or it may be physiological, and intended to act upon some associated organ, so as to make the effect of the remedy more favorable; or thirdly, to prevent some incidental, disagreeable result. An example of the former is where resin-bearing purgatives, or cholagogue agents, and a sedative like belladonna or hyoscyamus are introduced into a purgative pill; an example of the latter is where hydrobromic acid is added

to a cinchona preparation to prevent noises in the ears, or where carminatives are combined with a cathartic remedy, or the unpleasant effects of morphine are prevented by combining with it a small proportion of atropine. The object, not infrequently, may be purely pharmaceutical, as where a dry powder, as an excipient, is added in making pills. The third object of administering remedies in combination is to obtain as pleasant, or at least as unobjectionable, a form as possible.

When a remedy is exhibited in a form that the patient is utterly unable to swallow it, or is so repulsive that each dose causes nausea or vomiting, no matter how correct the prescription may be from the therapeutic standpoint, the patient will pronounce it a failure, and will probably relieve his feelings by uttering maledictions upon the doctor. On the other hand, if the remedy be attractive in appearance and pleasant to the taste, it will be regarded as a signal success, even though of less therapeutical activity. An agent is sometimes given merely for the mental and moral effect, without having any medicinal action directly. Such a combination is called a placebo, because it is administered simply to please the patient. Although placebos are rarely resorted to, patients should always be well treated, and with a little care much can be done toward making preparations pleasant. In choosing a physician, the voice of the patient would, in the majority of cases, be given, without hesitation, in favor of the prescriber who orders pleasant medicine, over him who has a special reputation for giving intolerably nasty ones. The young physician can get a hint from this which may greatly contribute to his success in after-life. Hence, a practical acquaintance with the expedients which modern elegant pharmacy offers, for overcoming the objectionable character of remedies, is of the highest service, has no mean intrinsic value from a financial point of view. A few suggestions for prescribing may be given here. Solid medicines may be given in compressed pills, coated with chocolate, in pills sugar- or gelatin- coated, in hard or soft capsules, or in suppositories. Powders can be given in cachêts de pain, gelatin capsules, or suspended in a dense syrup or other vehicle (such as stewed fruit or currant-jelly). Soluble or fluid agents, if unpleasant, are more difficult to hide, but they may be given in combination with aromatic or orange elixir, some fruit-syrup or in aromatic water. Many illustrations will appear, and formula will be given of good forms of combination, in the discussion of individual drugs under each head. A proper understanding and appreciation of this principle of combination will not only make the remedies more effective, but the patient will be less likely to forget to take his medicine, and thus will co-operate with the physician rather than oppose him in every possible way. This is seen to the best advantage in the management of sick children, where the remedies must be palatable or the struggles of the child to escape a nauseous dose may cause the attendant to give up in despair and conclude that the excitement may do the child more harm than the medicine will do him good.

In combining our remedies the question of incompatibility demands. consideration. Remedies may be (1) pharmaceutically incompatible, (2) chemically incompatible, or (3) physiologically incompatible. Agents are pharmaceutically incompatible when the proposed combination is either impracticable or extremely undesirable. Thus, the addition of water to a tincture of a resin-bearing drug precipitates the resin, or oleoresin, which floats upon the surface, thus spoiling the appearance of the preparation, and

possibly permitting too large a quantity of the active principle to be taken with the first doses from the bottle. As a rule, such tinctures should not be combined with solutions, aromatic waters, or infusions. Preparations of vegetable drugs containing tannic or gallic acid should not be prescribed. with iron, as this combination produces an unsightly mixture, and the iron is precipitated in an insoluble form. A survey of the Materia Medica will afford many instances of the ineligibility of particular remedies in certain forms of combination. Volatile and corrosive substances, or hygroscopic bodies, should not be given with powders; bulky drugs should not be added. to pills. In alkaloids of great physiological activity, such as strychnine, delphinine, or aconitine, the pill-form should not be resorted to on account of the danger of unequal mechanical division, and, in solution, it should be seen to that nothing be added that would render them insoluble. Some of the combinations, inexpedient from a pharmaceutical standpoint, are as follows:

(a) Form Explosive Compounds.-Chlorate of potassium and tannic or gallic acid. Bromide and alcohol. Nitrate of silver and creosote, or vegetable extracts containing glucose. Iodine and solutions of ammonia. Chromic acid and glycerin. Chloride of lime with sulphur. Spirit of nitric ether with certain fluid extracts. Calcium or sodium hypophosphite, with dry powders, or when triturated alone.

(b) Form Unsightly or Undesirable Mixtures.-Chloral with solutions containing alcohol. Vegetable tinctures containing oils and resins with water. Spirit of nitrous ether with potassium iodide, iron sulphate, tincture of guaiac, antipyrin, mucilage, tannic and gallic acids. Compound infusion of gentian with infusion of wild cherry or of cinchona. Copaiba and oils. with watery preparations (unless suspended by acacia or other emulsifying agent). Acids with ammoniated glycrrhizin.

Chemical incompatibility is caused by chemical decomposition with the production of a compound (salt) having characters and reaction different from its components. It should be avoided, as the rule, except where expressly intended by the prescriber. A knowledge of chemistry will generally put the physician upon his guard, but there are special illustrations, which must be borne in mind, where the combination is particularly undesirable, and, when ordered in a prescription, will defeat the object of the treatment and bring discredit upon the attendant. The general rules of chemical incompatibility are usually stated as follows:

As a rule, a remedy is not to be ordered in combination with its antidotes and chemical tests, especially if the latter depend upon the formation of an insoluble precipitate or a corrosive or poisonous salt. Thus, alkaloids are usually precipitated by mercurials and other metals, and may be destroyed by compounds containing free chlorine, caustic alkalies, or potassium permanganate. Tannic and gallic acids usually precipitate the alkaloids in a nearly insoluble form. The alkalies usually cause precipitation when added to solutions of metallic salts. Glucosides are decomposed by free acids or by emulsions.

Special incompatibilities will be studied in connection with individual drugs. Among those that are most likely to give trouble are preparations containing corrosive chloride of mercury, silver nitrate, solutions of iodine and iodides, arsenic, lead, quinine, strychnine, and tannic acid, and, as the rule, such combinations should be avoided and the agents given by them