MODE OF ACTION OF MEDICINES.

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also, by removing the obstacles to cure, become indirectly vivifying orrenovating stimuli ; and they may themselves, by disturbing the balancein a part, produce symptoms of irritation. If used in excess, they eithergive rise to the injurious effects of the heterogeneous stimulants, or, byinducing a sudden change of composition, annihilate the vital force, as isthe case with the narcotics. Since, however, such alterative medicinesaffect the composition of an organ each in its own way, one alterativemay, after a time, lose its influence, as it were, by saturation, while theorgan may still be susceptible of the influence of another. A great num-ber of the instances of habituation are referable to this cause.”

Such are the statements, as to the operation of medicines, made hy oneof the first physiologists of the age. They deserve careful and attentiveexamination. But however plausible they may appiear, the student is notto be unmindful that, for the most part, they are opinions merely, andthat the chemical changes in the tissues, so frequently referred to, havenot been as yet demonstrated by chemical analysis. Furthermore, Iwould refer those who are desirous of becoming acquainted with thearguments which have been adduced against the chemical action ofmedicines on the system, to Vogt’s Pharmakodynamik, bd . i. p. 9, et seq.The only chemical change which this author will admit medicines to becajpable of producing, is that which takes place in the parts to which theyare applied.

c. Dynamical. —The above-mentioned mechanical and chemical in-fluences are considered by many writers insufficient to explain the effectscaused by the greater number of the articles composing our MateriaMedica; principally on the ground that substances which exercise amost potent influence over the organism, frequently do so without pro-ducing any obviously mechanical or chemical changes in the conditionof the body. A third mode of operation has, therefore, been admitted,which is unattended with any recognizable changes of form or ofcomposition.

In the inorganic kingdom we have also evidence of an influencewhich cannot be denominated either mechanical or chemical. The com-munication of magnetical and electrical properties to iron by merecontact with another body, without the production of any change of formor of composition, either of the iron itself or of the imparting body, isan example of this. Now to influences of this kind the term dynamicalhas been applied; and in several pharmacological works, (among whichare Burdach ’s System der Arzneymittellehre, C. II. E. BiscliofFs Hand-buch der Arzneimittellehre, and Vogt’s Lehrbuch der Pharmakodynamik ),it is employed to indicate those influences of medicines over the organismwhich are ascribable to neither mechanical nor chemical causes.

Some have attempted to account for the action of medicines on elec-trical principles. All bodies, says Bischoff, (op. cit. bd. i. p. 158,) bycontact with each other, act as electrics, without, however, necessarilyundergoing any chemical changes. Therefore, when a medicine isapplied to the organism, its action is electrical (p. 162.) But though,says this writer, a medicine may produce electrical without chemicalchanges, yet the reverse of this docs not hold good, for no chemicalchanges can occur without the production of alterations in the electricalcondition of bodies (p. 163); and, consequently, the operation of causticsis an electro-chemical process.