Every one is familiar with the fact that cold has a tendency to increase the secretion of urine. Whether applied to the stomach, the rectum, or the surface of the body, the effect is the same. More urine is passed in winter than summer. The drinking of a glass of ice-cold water, walking bare-foot over a cold floor, or exposure of the body to the cold air, will often in a short time be followed by a flow of urine. This effect is no doubt in part owing to the checking of the sensible or insensible perspiration, possibly also of the pulmonary exhalation, and that of the gastro-intestinal mucous membrane, in consequence of which, the blood, and the matters ordinarily eliminated by these methods, accumulate in the blood-vessels, and of course operate with increased energy on the kidneys, as the only outlet for their escape. But I believe also that such a relation has been established, in our original constitution, through the medium of the nervous centres, between the kidneys and an impression of cold anywhere upon the body, that, when the latter is experienced, the former are called into increased action. The intention is obvious. Coldness, below a certain standard, is an abnormal state of system, against which nature must provide. To prevent injury from its sedative influence, some counter-agency must be brought into operation. Of this nature is the disposition to reaction, of which I have already sufficiently treated. But there is also another. The perspiration and pulmonary exhalation, through the vaporization of the liquid eliminated from the blood-vessels of the skin and bronchial membrane, are a never-ceasing cause of reduction of temperature. But as this is not now wanted, cold has a tendency to check it; and thus one mode of obviating the effects of cold, and restoring the reduced temperature to the proper mean, is put into operation. But the accumulation of liquid in the circulation, consequent on the suspension of these two functions, might do harm, unless some obviating influence existed. This is provided for by those sympathies which determine that cold should directly increase the urinary secretion. Such is the rationale of the operation of cold as a diuretic.

We may often very happily avail ourselves therapeutically of this influence, in aiding the operation of diuretics. Thus, when medicines of this class are exhibited, the patient should take cold drinks, should expose himself moderately to the cold air, and should generally be encouraged to sit up or walk about, rather than lie warmly covered in bed. But care must also bo taken not to abuse the influence. if the cold be too strongly, or too steadily applied, independently of its depressing effects, there may be danger of a morbid accumulation internally of blood and nervous power; and high vascular irritation or inflammation of some internal organ, perhaps of the kidneys themselves, may be induced, which, instead of increasing, may diminish or suspend their function.