Medicinal Combination. “_Longum est iter per Præcepta, breve et efficax per Exempla._” SENECA. A COLLECTION OF FORMULÆ INTENDED TO ILLUSTRATE THE FOREGOING PRECEPTS, and to furnish the inexperienced Prescriber WITH A SERIES OF _USEFUL AND INSTRUCTIVE LESSONS_. EXPLANATION OF THE KEY LETTERS. The _Modus Operandi_ of the different elements of each formula is designated by a KEY LETTER, or _Symbol_, which is printed in a different type, (thus =B=) and placed in the margin opposite to each. This letter refers to a corresponding one in the Synopsis, and thereby shews the division containing an exposition of the principles upon which the operation of the ingredient is supposed to depend. Two or more KEY LETTERS denote that the element against which they are so placed has several modes of operation, whilst the order in which the letters succeed each other, serves to shew the relative importance of them. Where any one of the letters is _small_, _i. e._ not a capital, it denotes that the operation which it is intended to express is only _incidental_ to, or subordinate in, the general scheme of the combination. When any number of elements are included within a _vinculum_ or bracket, it is intended to shew that they operate but as one substance, or, that the virtues of each are not independent of the other; in this case the KEY LETTER within the bracket expresses upon what principle this unity depends, whilst that on the exterior shews the action of such a combination upon the base, or the part which it performs in the general scheme of the Formula. Let us exemplify it by a reference to _Formula 78_ which presents us with a Purgative, in conjunction with a Stimulant. The base is _Aloes_, which is succeeded by _Scammony_, and _Extract of Rhubarb_; these substances appear by the bracket, to act in unison, a concurrence which the interior letter =B= shews to depend upon their being SIMILAR REMEDIES; the letter also on the exterior shews that its operation upon the base depends upon the same principle. We next come to powdered _Capsicum_, and _Oil of Cloves_; these ingredients are also shewn by a bracket to act in unity, and the letter =B= in the interior, denotes that it is in consequence of their possessing a similar mode of action, whilst the letter =G= on the exterior, announces that they act in the general scheme for the purpose of fulfilling a second indication; at the same time the smaller letter _e_ informs us that the combination likewise acts as a _corrector_ of the base.[315]