Of the heat generated within the body by exercise, stimulation, rich diet, friction, etc., I shall not here treat, because it is a result of other measures, and, though it may be one of the means by which those measures prove remedial, it cannot be itself considered in the light of a remedy.

There are two modes of obtaining the direct influence of heat; first, by preventing the escape of the natural heat of the body, and thus causing its accumulation, and secondly by imparting it to the body from other heated substances.

1. Confining the Heat of the Body

This is effected by surrounding the person with a badly conducting medium in the form of clothing, or bed-covering at night, or in that of a dry atmosphere, which is a very slow conductor.

a. Clothing. Much may be done in the management of morbid tendencies, and even of disease itself, by a proper regulation of the clothing.

Furs, feathers or down, and wool are the worst conductors of heat; tissues made of raw silk are, perhaps, next in order; then tissues of cotton, and after this linen, which is the most rapid conductor of all the materials used for clothing. It is obvious that, when the object is to keep the surface warm, a selection should be made from these substances, whether for body clothing, for bedding and bed-covering at night, or for occasional use under extraordinary exposures to cold, according to the degree of protection wanted; the worst conductors being chosen when it is most important to confine the animal heat. Upon the whole, the most suitable under-clothing for keeping up an equable temperature of the body is flannel, or the elastic woollen tissue now so much worn, which has the advantage over flannel that it shrinks less by washing, and is not apt to become so hard and stiff. When it is specially important to preserve an equable temperature, this should be worn through the whole year, summer as well as winter; the quality being accommodated to the degree of heat. The fabric may be had of every diversity of texture, from the coarseness of the heaviest flannel, to the fine almost of gossamer; and the lightest should be chosen for summer wear. It is scarcely less important in the warm than the cold season; for the changes of summer are very great, and the surface is even more suserp-tible to cold than in winter, in consequence of its frequent relaxation under a high temperature. Should even the lightest woollen fabric be insupportable in the most intense heat of the season, a similar tissue made of raw silk may be substituted, or, if this cannot be had, of cotton; but, in cases of delicate health, where the preservation of the temperature is important, linen should never be worn next the surface of the body, unless when the skin is excessively irritable; and, in that wool, silk, or cotton should be worn over it. Persons in whom this kind of caution is essential, should be peculiarly careful to keep the feet warm and dry, either by woollen stockings, or, what is sometimes preferable, double stockings, one pair of silk, and the other of cotton. Oc-casionally, woollen hose keep the feet in a constant perspiration, which moistens the covering, and serves to convey away the heat; so that these parts are always cold. This evil may often be corrected by wearing the double hose just referred to. In wet weather, the boots or shoes should always be water-tight, when the person is exposed out of doors; but they should be exchanged for others within doors, as they confine the perspiration, and cause the feet to be cold by making them damp. The outer covering should always be proportioned to the degree of cold, when the body is necessarily exposed to it. Some delicate individuals think they can harden themselves against cold, by habitual exposure; and hence encounter the severest weather with insufficient covering. This is a great mistake. They frequently, I believe, expose themselves in this way to the great danger of aggravating a morbid diathesis into positive disease. The proper rule is never to allow one's self to become chilled for any length of time. An excellent mode of preventing the evil results of the present fashion of open dressing over the chest, is to suspend from the neck, under the shirt, a piece of doubled silk with cotton wadding quilted within, or a dressed rabbit's skin. At night, equal attention is necessary to preserve a due degree of warmth. The covering should be sufficient to render the person comfortable; and, with delicate persons, it is better to err on the side of excess of warmth than that of cold. The habit of using mattresses in summer is very well; but feather beds should be employed, in winter, by all persons in whom the indication for sustaining a warm temperature of the body exists. I think I have known the most serious evils result from an attempt, on the part of individuals of scrofulous predisposition, to harden themselves to the influence of cold; and carelessness on this point may be equally injurious. It will be observed that I am not applying these remarks to the healthy and robust. For these, equal caution is not necessary; though even they would do well to exercise some care in the point under consideration.

The predispositions and affections to which these observations are especially applicable are those of a scrofulous or tuberculous character. A continued depression of temperature beneath that of full health is peculiarly injurious in all the forms of tuberculosis, whether before or after the deposition, and in all cases of a strumous character or tendency. Hence the advantage, on the part of such individuals, of a residence in warm climates; but, when this is impossible, much can be done by a due attention to clothing, by day and by night, and at all seasons. I do not say that temporary exposures to cold may not sometimes be useful in these persons, through the tonic influence of the reaction. But such exposures should always be purposed, not accidental; should be employed in a remedial capacity, and not left to the caprices of chance; and, when they are resorted to, the utmost care should be taken that due reaction shall ensue. When this takes place with difficulty, they should be at once abandoned. The above remarks may seem trivial to the inexperienced; but those who have seen much of disease know, that influences of the kind here alluded to are quite as important as medi-cines, and will agree with me in the necessity of attention to them.

But it is not in the scrofulous cachexia only that a due preservation of warmth is important. All low forms of disease, and especially the low fevers, are promoted by constant chilliness; and no fact is more universally admitted in medicine, than that change of temperature, and especially exposure to cold after heat, is one of the most fruitful causes of the various inflammations. The preservation of a moderate warmth of surface, not sufficient to induce perspiration, is one of the great hygienic rules which should be attended to under all circumstances.