3. Temperament

Temperament should receive some attention in the administration of medicines; but the judicious physician will probably be influenced in relation to it more by his general principles than by any special precepts. The sanguine temperament obviously demands caution in the administration of stimulants, and the nervous in that of evacuants: while the phlegmatic, being characterized by a general deficiency of susceptibility, admits and requires a freer use of medicines in reference to a given effect.

4. Idiosyncrasy

Individual peculiarity, technically denominated idiosyncrasy, is of much greater importance, and can scarcely receive from the physician a too careful attention. In very many individuals, perhaps it may be said in nearly all, there is some peculiarity, in relation to the effects of a particular medicine, or possibly of more than one, which, if unknown or neglected, may lead to serious inconvenience or injury, and even to fatal results. This peculiarity sometimes consists merely in an excessive susceptibility, or in an abnormal insusceptibility to the action of the medicine or medicines; so that an ordinary dose might, in the former case, act with dangerous violence, and in the latter not act at all. This is strongly illustrated in the not unfrequently unex-pected results from the use of the mercurial preparations. In more than one instance that might be adduced, a moderate dose of calomel or other mercurial has acted so powerfully, in consequence of a remarkable constitutional susceptibility to its influence, as to occasion death; and ever}* experienced practitioner, who has used this medicine habitually, must have witnessed instances of unexpected violence in its action; while, in other cases, from defective susceptibility, it is quite impossible to bring about its peculiar effects on the system by any quantity that can be given, with any regard to prudence. The instance of rnercury has been brought forward simply as a striking example; but there is scarcely an efficient article of the materia medica, in relation to which there does not exist, in some one or more persons, a similar excess or deficiency of susceptibility. But the idiosyncrasy is not unfrequently also of such a nature as to render the effects of a medicine altogether different from those which it ordinarily produces. The well-known and often-cited example of ipecacuanha, in causing by its mere smell an asthmatic paroxysm in certain persons, is strikingly illustrative of this fact. Other examples are offered in the cutaneous eruption produced in some individuals by copaiba and the turpentines, the irregular and very inconvenient effects sometimes resulting from opium, and the occasional peculiar and poisonous operation of mercury, altogether different from its proper action. I have known so innocent a medicine as pipsissewa (Chimaphila umbellata), given in the form of decoction, in the dose of a wineglassful, to cause a most violent attack of erythematous inflammation of the mouth and face.

These idiosyncrasies are sometimes also developed by disease, so as to render individuals susceptible to effects from medicines quite different from those expected, and sometimes even directly opposite.

Whether original or acquired, they should claim the careful attention of the practitioner, who should never neglect information in reference to such peculiarities that may be volunteered by the patient, and should lay up in his memory, for future use, all that he may witness in his own experience or observation. A physician thoroughly acquainted, from habitual attendance, with all the constitutional peculiarities of his patient in reference to the effects of medicines, often has great advantages in treatment over others without any experience of the kind.

5. Disease

Reference has already been more than once made to the influence of disease in modifying the effects of medicines. Not only is the susceptibility to their influence greatly increased in some instances, and greatly diminished in others, but new susceptibilities are occasionally awakened, and effects wholly abnormal, or at least apparently so, are experienced. Thus, inflammation of the stomach so much increases the susceptibility to the influence of emetics, that a minute fraction of the ordinary dose will often operate; while, in certain nervous affections. as delirium tremens for example, there is an almost equal diminution susceptibility, and, in some instances, enormous doses are required to produce vomiting. In certain morbid conditions of the brain, a little opium will excite to phrensy; in others, it is with the ulmost difficulty that the medicine can be brought to operate, as in tetanus and certain forms of mania. In diarrhoea, opium often checks the evacuation colic, on the contrary, favours the action of cathartic medicine. Certain conditions of disease have a powerful influence over the effects of medicines by impeding their absorption. Thus, any morbid state of the liver, which retards the circulation of the portal blood through that organ must produce general congestion of the bowels, and consequently offer a strong impediment to the entrance of the medicine into the circulation. But, in this place, all that is necessary is simply to notice the modifying influence of disease, and to impress on the mind of the student the indispensable necessity of attending to it. The peculiarities in this respect of different morbid states, must be studied along with the several diseases in which, or the several medicines in reference to which, they are displayed.

6. Climate

Climate acts by altering the state of the system. Sometimes the change is so great as to amount to disease; and then the influence of this modifying cause is merged in that of the one last considered. But climate also affects the functions in a manner which can scarcely be considered pathological; as the result is experienced more or less by the whole community; and, though the state of system under any particular climatic influence may be less vigorous, or less perfectly balanced, than under more favourable circumstances, it is nevertheless the health of that region where the influence prevails. The following may be mentioned as examples of the modifying influence of climate over the effects of medicine. In cold climates the susceptibility to alcoholic stimulants is much less than in the hot; probably because, in the former, much of the stimulant is consumed in the lungs for the production of heat, and thus thrown off from the system; while in the latter, in which heat is already in superfluity, none of the alcohol is consumed in the lungs, and more of it is consequently retained to act upon the brain. In hot climates, calomel acts less energetically on the liver than in cold, probably from the diminished general susceptibility of that organ, consequent upon its habitual over-excitement. In miasmatic districts, blood-letting and other evacuant measures are, in general, not so well borne as in regions exempt from malarial influence; while quinia may be given with a freedom which elsewhere might be hazardous. But the modifications produced by climate in the operation of medicines have not been investigated with sufficient accuracy and precision, to justify anything more than very general statements upon the subject.