It not unfrequently happens that abbreviations are productive of direful errors, and there are some special instances to which I will now ask your careful attention. If you desired to prescribe acidum hydrochloricum, you might possibly write "acid. hydroc."—an abbreviation which would equally stand for acidum hydrocyanicum, and grave consequences might ensue from such a reading. Again, in writing the words aqua fontis, the n should be perfectly legible, lest the words might be mistaken for aqua fortis. You should be careful when writing colchicum or colocynth not to use the abbreviation "col.," for the dispenser would then be left in doubt as to which drug was intended. I have seen several prescriptions in which the contraction "hydr." occurred—a word which might mean either hydrargyrum, hydras, hydriodas, hydrochloricum, or hydrocyanicum. The abbreviation "hydr. bic." might be intended for the bichloride or bicyanide of mercury, and "hydr. bin." would equally signify the

biniodide or the binoxide of that metal.

Short a time as hydrate of chloral has been in use, the words “hyd. chlor.," which were written for it, have been taken to indicate corrosive sublimate.

The foregoing are some of the more important instances of the errors which might ensue from the careless or injudicious use of abbreviations. I trust that they will demonstrate forcibly the necessity of carefully considering the significance which might be attributed to every abbreviation you make use of

LESSON V.

THE PRINCIPLES OF MEDICINAL COMBINATION.

Over sixty years ago Dr. John Ayrton Paris published his Pharmacologia,' many copies of which can yet be had. In this work the principles of medicinal combination have been treated in so exhaustive and masterly a style, that no subsequent writer has found room for improvement. I shall not attempt originality, therefore, in this lesson, but will endeavour as briefly, but as faithfully as possible, to give you the pith of Dr. Paris's teachings. I should, however, advise you to endeavour to procure for yourselves a copy of this work, which is as intelligible to the most junior student as it is pregnant with interest to the veteran practitioner, every page of it teeming with fact, observation, and suggestion,

The objects which we seek to obtain by combining medicines are fourfold :—

Ist. To augment, correct, or modify the action of a medicine.

2nd. To obtain the joint operation of two or more medicines.

3rd. To obtain a new remedy.

4th. To afford a suitable form.

These objects we will consider seriatim.

I. TO AUGMENT, CORRECT, OR MODIFY THE ACTION OF A MEDICINE.

are

We can AUGMENT the action of a medicine by combining different preparations of it, as, for instance, when the infusion and tincture of the same substance are ordered, a combination which is indicated when all the active principles are not soluble in the same vehicle. Another means of increasing the action of a substance is by combining with it substances which produce similar effects. To Dr. Fordyce we indebted for the enunciation of the law that "combination of similar remedies will produce a more certain, speedy, and considerable effect than an equivalent dose of any single one." Neither ipecacuanha nor tartar emetic alone are so certain as a mixture of the two when we desire to produce emesis. Every class of therapeutic agents affords numerous examples of the truth of this law. I trust that I have only to mention that the subject offers a wide field for original research to stimulate you to seek out for yourselves fresh illustrations of the law of Fordyce. A third and last

mode of increasing the action of a medicine is by combining with it substances of a different nature which can in some unknown manner enhance its action. The diuretic effect of squill is increased by a mercurial; ipecacuanha assists the purgative action of jalap; and opium renders more certain the action of mercury. Other examples innumerable might be quoted as afforded both by officinal and magistral formulæ.

We can CORRECT or MODIFY the action of a medicine by chemically neutralising, or mechanically separating, the offending ingredient, or by combining with it some substance capable of protecting the stomach or system against its injurious effects. Thus, we correct the griping tendency of purgatives by combining with them aromatics or essential oils; the drastic properties of colocynth may be obviated by admixture with camphor. The griping of senna and resinous purgatives may be prevented by alkaline salts; and several substances can be deprived of acrimony by trituration with mucilage, barley-water, or milk, as exemplified by the mistura scammonii of the Pharmacopœia. Again, the tendency of mercurials to affect the bowels. may be corrected by opium, while the constipating effects of the latter drug may be best combated by combination with aloes.

II. TO OBTAIN THE CO-OPERATION OF TWO OR MORE MEDICINES,

This we do by combining substances which have a different mode of action, and which effect the same or different results. As an example of a combination of