While the business of the physician is more especially the care of the sick with reference to the cure of disease, or, where that is beyond his power, as is too frequently the case, to relieve suffering and secure temporary ease for his patient, he is nevertheless often called upon to answer questions as to the causes of disease, and the best means of avoiding or destroying these causes. Not only does diagnosis often turn upon considerations of etiology, but a very considerable part of the treatment of actual disease must be hygienic in the broader sense of the word. The prescription or the surgical operation must not only be supplemented by advice as to residence, clothing, food, exercise, etc., but must, in many cases, be merely supplementary to such advice, which indicates the really essential method of treatment; and the giving this advice then becomes the most important part of the physician's work, although not usually recognized as such by his patients. The chief value of the prescription is, in fact, often to methodize the mode of life of the patient and to remind him at frequently recurring intervals of the regimen which has been ordered with it. The physician has also certain duties in relation to the public at large, as well as to his individual patients, and these duties become more numerous and important as the density of population increases, so that in the large cities of most civilized countries he finds himself, nolens volens, in almost daily contact with legally constituted authorities in the shape of registrars, health officers, coroners, etc., and is not infrequently summoned before the courts as a supposed expert in matters connected with the public health. Moreover, the physician who has become eminent in his profession is, in many cases the adviser, and, so far as professional subjects are concerned, to a great extent the guide, of those who legislate for, or execute the laws of, not only his own city or county, but his state and the nation; and he must to a corresponding degree be held responsible for the position which he takes and the advice which he gives in regard to public health matters. This is true whether his attitude on these subjects {174} be active or passive, for his silence will be taken to mean that there is no necessity for action or change. The limits of this paper do not permit the presentation of proofs and illustrations of these somewhat dogmatic assertions, but it is believed that they will meet with general assent from medical men without formal and detailed argument, and that it is unnecessary here to urge the interest or importance of practical hygiene upon the medical profession, or to enlarge upon the desirability that the practitioner, as well as the professional sanitarian, should be familiar with the conclusions of modern science and technology with regard to it.