The experience of the profession must, I think, run parallel with that of the wisest of its individual members.  Each time a plan of treatment or a particular remedy comes up for trial, it is submitted to a sharper scrutiny.  When Cullen wrote his Materia Medica, he had seriously to assail the practice of giving burnt toad, which was still countenanced by at least one medical authority of note.  I have read recently in some medical journal, that an American practitioner, whose name is known to the country, is prescribing the hoof of a horse for epilepsy.  It was doubtless suggested by that old fancy of wearing a portion of elk’s hoof hung round the neck or in a ring, for this disease.  But it is hard to persuade reasonable people to swallow the abominations of a former period.  The evidence which satisfied Fernelius will not serve one of our hospital physicians.

In this way those articles of the Materia Medica which had nothing but loathsomeness to recommend them have been gradually dropped, and are not like to obtain any general favor again with civilized communities.  The next culprits to be tried are the poisons.  I have never been in the least sceptical as to the utility of some of them, when properly employed.  Though I believe that at present, taking the world at large, and leaving out a few powerful agents of such immense value that they rank next to food in importance, the poisons prescribed for disease do more hurt than good, I have no doubt, and never professed to have any, that they do much good in prudent and instructed hands.  But I am very willing to confess a great jealousy of many agents, and I could almost wish to see the Materia Medica so classed as to call suspicion upon certain ones among them.

Thus the alien elements, those which do not properly enter into the composition of any living tissue, are the most to be suspected, —­mercury, lead, antimony, silver, and the rest, for the reasons I have before mentioned.  Even iodine, which, as it is found in certain plants, seems less remote from the animal tissues, gives unequivocal proofs from time to time that it is hostile to some portions of the glandular system.

There is, of course, less prima facie objection to those agents which consist of assimilable elements, such as are found making a part of healthy tissues.  These are divisible into three classes,—­foods, poisons, and inert, mostly because insoluble, substances.  The food of one animal or of one human being is sometimes poison to another, and vice versa; inert substances may act mechanically, so as to produce the effect of poisons; but this division holds exactly enough for our purpose.