MODE OF ACTION OF MEDICINES.

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p. 164,) observes, that from this inferior developement, the brain of the dog“ is not so liable to sanguineous congestion, and when this condition isobserved, it is not very intense—stupor is the only symptom of it; nevercoma, loss of consciousness, nor profound sleep.” I have observed thatthe root of monkshood does not act precisely alike on rabbits and dogs.In the latter, one of the most remarkable symptoms of its operation isdiminution of feeling; in the former, the function of feeling is much lessobviously affected, but we observe more evident paralysis of the hindextremities. Differences of this kind are to be expected^ since theyare connected with unequal developement of the nervous system. Asrabbits and horses cannot vomit, irritant poisons when administered tothem cannot act as emetics. The skin of horses is more susceptiblethan the human integument of the action of turpentine. On the otherhand, certain agents, whose operation on the human body is most ener-getic, have, comparatively, very little effect on the horse—as colocynth,briony, and jalap.— ( Moiroud, Pharmacologie Veterinaire, pp. 269 and274.)

On man.- —The action of medicines on the dead human body, or onparts separated from it, as the blood recently drawn from the veins, hasbeen examined, with the view of learning the operation of these agentson the living body. It may be of assistance to us in ascertaining eitherthe mechanical or chemical action of substances ; but as the greater num-ber of medicines act only on the living body, and quite independently ofany known mechanical or chemical influences, this mode of investigationis of very limited value.

In ascertaining the action of remedial agents on the living body,it is necessary that we examine their influence both in healthy anddiseased conditions. For, by the first we learn the positive or actual powerof a medicine over the body ; while by the second, we see how that poweris modified by the presence of disease. Moreover, in the latter conditionwe sometimes discover remedial influences which our knowledge of theeffects of medicines on the healthy body could not have led us to antici-pate. The beneficial operation of arsenious acid in agues, or in lepra,could never have been inferred from any experiments made with thissubstance in health merely; nor could we have formed a correct estimateof the effects and proper dose of opium by employing it in tetanus, norby using mercurials in fever. The homceopathists assert, and with truth,that the study of the effects of medicines in the healthy state is the onlyway of ascertaining the pure or pathogenetic effects of medicines—:sincewhen we administer our remedies to invalids “the symptoms of thenatural disease, then existing, mingling with those which the medicinalagents are capable of producing, the latter can rarely be distinguishedwith any clearness or precision.”— ( Hahnemann's Organon, translated byC. H. Devrient, p. 190.)

3. Mode of Action of Medicines.

The production of effects by the application of medicines to the livingbody, depends on the existence of two classes of powers or forces; the onein the medicine, the other in the organism.

1. Active forces of Medicines. —Bodies act on each other in one ormore of three ways, viz.: mechanically, by their weight, cohesion, exter-nal form, and motion; chemically, by their mutual affinities; and dynami-