The peculiarities of constitution and temperament, and par' ticular susceptibility to external impressions and influences, possessed by different individuals and included in the general category of idiosyncracies, have been a puzzle and a snare to the theoretical physiologist since the days of Galen. Such peculiarities are not confined only to the body, but are frequently to be detected in the mind. The writer of this article is a descendant of families distinguished through several generations, both on the maternal and paternal side, for idiosyncracies, and is himself affected by a peculiarity to which his family physician can testify, and which will hardly be credited by other physicians. Opium in large doses is to him a cathartic. Very few cases of this peculiarity are to be met with. We once heard a distinguished professor of materia medica, assert in a lecture the possibility of this action of opium upon persons of peculiar constitution, unconscious that a living example of the fact was listening to his words. All idiosyncracies are of course remarkable as seeming exceptions to general laws, and there is nothing more so about the one mentioned than anyothei,exceptthe rarity of its occurrence. We hav e met, indeed, with a physician of this city, who has known a similar case in Europe, but this is the only other case of the kind we ever heard of. On the whole we are inclined to think idiosyncracies much more common than is generally supposed, many escaping notice on account of their unimportant character. One of the most common classes of idiosyncracies are those connected with eating and drinking. Almost every one is ac quainted with somebody who cannot eat honey without subsequent distress at the stomach. Not quite so common are those who cannot eat the flesh of certain kinds of animals. A number of cases are recorded of those who could not eat mutton without poisonous effects. An instance* of this kind once came within our personal knowledge. Supposing it to be purely the effect of imagination, the mutton was once smuggled into mince pies, usually made with beef, and thus disguised was eaten, by the person affected, withquite serious results. Violent pain in the stomach and sickness, followed by copious vomiting, in fact nearly all the symptoms of irritant poisoning succeeded the eating of the mutton in this case, and although the vomiting relieved the more distressing symptoms, the effects were felt for several days. Similar effects from eating mutton are recorded in the books. Even the most mild, and apparently most harmless, articles of food may prove baneful to some people. Rice, cheese, eggs, and various kinds of fruits, as strawberries, oranges, and melons, have been known to invariably produce ill effects upon some peculiarly constituted individuals. There is scarcely one of our physical faculties that may not exhibit these idiosyncracies. Sight, smell, the sense of touch, and even hearing, may be thus perverted. How often we hear of cer tain sounds that the " set ones teeth on edge." We have read somewhere of women so sensitive to the effects of such, sounds that the whistle of a thread drawn through stiff cloth in sewing was positively unendurable. Nay, there seem to be instances where deleterious effects are produced by commonly harmless objects, when their presence is recognized by no sense in particular. Instances of the latter kind are perhaps as well or better authenticated than any others. Effects of this class are generally connected with the presence of animals, as cats, rabbits, etc, the near approach of which is noxious to the persons affected, as is also quite frequently the touch of their furs. All that we have stated is based upon the best authority and may be relied upon as perfectly credible. Now, how, we ask, disregarding such facts, can medicines be prescribed by rule, as is the too common custom, without occasionally -evil, nay, even disastrous results ? We have often had opium prescribed in the ordinary full dose with the view to produce the ordinary, but exactly the opposite effect, invariably resulting to us from its use. We have seen the feet and limbs of a young lady whose skin is peculiarly susceptible to poisonous effects, so swollen and inflamed from the effects of mustard drafts, as to excite fears of .the worst consequencss. We have seen similar effects from the application to the skin of carbolic acid. We have stood by hundreds of sick beds and have seen numberless doses prescribed, and hardly ever have heard a physician ask how certain medicines usually effect the patients. As a consequence, we have seen patients completely prostrated by the action of drastic purgatives, in doses that would not per-hapS have seriously injured the average patient. We have seen others completely narcotized by doses of morphine, that would only have quieted a cough in most; and so on to the end of the chapter. We are well aware that book doctoring is held at its proper Valuation by the leaders in the medical profession, and that to such, the really skillful, even the slightest peculiarity of temperament is not deemed unworthy of attention ; but there are too many, far too many, who put all patients on the same plane, and confine themselves rigidly to one routine of treatment. No less are idiosyncracies of mind and disposition to be regarded in imparting instruction to the young, or in our everyday dealings with our fellow men. Most mental peculiari ties are easily discovered by the practiced student of human nature, and it as much our duty in our attempts to instruct and reform others, to avoid nauseating them mentally as it is that of the physician to avoid over-dosing those he is attempting to heal.