34

ELEMENTS OF MATERIA MEDICA.

declines; but this certainly does not generally hold good with respect toemetic tartar, as will be mentioned hereafter. Dr. Marshall Hall{Researches relative to the Morbid and Curative Effects of Loss of Blood ,1830, also, Introductory Lecture, 1834,) maintains, that while a man inhealth can lose a given quantity of blood (say Sxv.) without fainting,the same individual, affected with congestion of the brain or inflammation,can bear a much larger quantity (as from Sxxx. to SI.) before inci-pient syncope,—while in fever, intestinal irritation, dyspepsia, or cholera,a smaller quantity (as from *vi. to gxii.) will occasion fainting:—so thatcongestion and inflammation augment, while fever, cholera, &c. diminishthe tolerance of blood-letting; he therefore makes use of this circumstanceas a diagnostic to enable him to distinguish irritation from inflammation.

9. Circumstances which modify the effects of Medicines.

The circumstances which modify the effects of medicines may bearranged under two heads; those relating to the medicine, and thoserelating to the organism.

1. Relating to the Medicine. - —Under this head are included,—

a. State of Aggregation. —The state of aggregation of a medicine mo-difies the effect. Thus morphia is more active in solution than in thesolid state.

b. Chemical combination. —The soluble salts of the vegetable alkalisare more active than the uncombined alkalis, and vice versa, the insolublesalts are less active. Lead and baryta are rendered inert by combinationwith sulphuric acid.

c. Pharmaceutical mixture. —The modifications produced by medi-cinal combinations have been very ably described by Dr. Paris.—(Pharmacologia , 6th ed. vol. i. p. 267.) The objects to be obtained, heobserves, by mixing and combining medicinal substances, are the fol-lowing :—

I. To promote the action of the basis or principal medicine : —

A. By combining together several forms or preparations of the same substance : aswhen vve conjoin the tincture, decoction, and extract of cinchona in one formula.

B. By combining the basis with substances which are of the same nature, that is,which are individually capable of producing the same effect, but with less energythan when in combination with each other: as when we prescribe a compoundof cassia pulp and manna.

C. By combining the basis with substances of a different value, and which do notexert any chemical influence upon it, but are found, by experience, to be capableof rendering the stomach, or system, or any particular organ, more susceptible ofits action: as when we combine mercury with antimony and opium, to increasethe activity of the former.

II. To correct the operation of the basis, by obviating any unpleasant effects it might

be likely to occasion, and which would pervert its intended action, and defeat the

objects of its exhibition.

A. By mechanically separating, or chemically neutralizing, the offending ingre-dient ; as by digesting Cetraria Islandica in an alkaline solution, in order toremove the bitter principle, and to enable us to obtain a tasteless, but highlynutritious fecula.

B. By adding some substance capable of guarding the stomach or system againstits deleterious effects ; as when we combine aromatics with drastic purgatives, tocorrect the griping qualities of the latter;—or opium with mercurials, to preventthe latter affecting the bowels.

III. To obtain the joint operation of two or more medicines.

A. By uniting those substances which are calculated to produce the same ultimateresults, although by totally different modes of operation: as when we combine