and it is considered to attain its maximum during the actual period of digestion, and especially when the chyle has reached the circulation, and is becoming converted into blood,-and, likewise, it is probable, that the secretion goes on more rapidly during sleep, than when the body is not undergoing positive exertion when awake. The exhalation from the skin is evidently to some degree antagonised by that from the pulmonary tissue, and still more so by the secretion from the kidneys. An excessive secretion of urine is always attended with a lessening of the amount of cutaneous exhalation; and, conversely, the renal functions are less energetic when the skin exhales freely. If the relative and equipoised action of the several emunctories of the system is suddenly or greatly disturbed, there is always a risk that the diminished secretion of one tissue or organ, may not be atoned for in due degree by the increased secretion from one or other of the other emulging structures, and that diminished waste, and unexpended effete matters, may lead to functional derangement, and eventual disorder of the economy of the body. Besides this necessary consequence of the cutaneous exhalations serving in so far an emulgent effect, and being a source of waste and expenditure to the system, these exhalations unquestionably serve the further purpose of diminishing the temperature of the body, and in so far aid in equalising the animal heat, under the differing circumstances of weather, season, and climate.

But this is not all. There is besides these purposes

SYMPATHETIC ACTION OF THE SKIN, ETC. 173

and effects, a sympathetic dependence between the several organs and functions of the body, that has to be recognised and allowed for a sympathy obviously communicated through the medium of the nerves which supply them with their properties and their powers. This sympathy subsists perhaps in an especial degree, between the skin and the mucous membrane. This is well illustrated by the chilled condition of the surface of the body, amounting at times to that called "goose skin," which the digestion of a heavy dinner so frequently occasions,— or which may be induced by the digestive process, whatever the quantity or the nature of the food that has been taken, when the system has been much weakened, whether from disease or over-fatigue. The converse of this is illustrated by the common occurrence of indigestion, when the surface of the body is chilled by exposure to a cold and wet atmosphere. The first of these cases might be partly explained, by the fact that so much more blood would have to be directed to the stomach, to enable it to digest so large a mass of food, or a meal that, however small, might prove to be disproportioned to the enfeebled condition of the system; but the other case involves an exclusive appeal to sympathetic action for its explanation. As further illustrations of this curious and important connection between different and remote organs and textures, it may be mentioned that when, either from excessive heat or excessive cold, the powers of the skin are depressed, those of the stomach are usually depressed too. Few men

are happy enough to retain their appetites in a hot summer's day, or in the cold and damp day of winter. On the other hand, if the cold or the heat is not sufficient in its degree, to overcome the powers of the system, but only serves to rouse it into an effort to resist such influence, the effect is to increase the energies of the skin; and the energies of the stomach are found to be, in an equal ratio, excited and increased.

The inference from such facts is obvious, that, to preserve the due balance of the circulation,—a balance which cannot be disturbed without some degree of consequent congestion, and without risk of setting up inflammation in some of the organs; to encourage the cutaneous exhalation,—a secretion which cannot be materially lessened in its degree without involving a corresponding degree of fulness of the blood-vessels, a fulness which is almost always fraught with danger; and to prevent the sympathetic disorders of other organs, which are so apt to follow a disturbance of the functions of the skin; it is necessary that the surface of the body should be protected by such an amount of clothing, as shall be uniformly proportioned to the climate and the season.

Substances part with their heat in two ways: the one by contact, the other by radiation. I have at present only to do with articles of clothing. So far as these are concerned, both modes must be briefly considered.

Some substances neither readily receive, nor readily part with heat; others receive it quickly, and part

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with it quickly. The former are called bad, the latter good conductors of heat; the former are warm to the touch, the latter are cold; the bad conductors afford the best protection against the cold, the good conductors afford the least protection against it; the bad conductors confine most completely the animal heat, the good conductors allow it the most readily to pass through them. The following, beginning with the best conductors, may be considered to be the order in which they ought to be classed :—

1. Flax.

2. Cotton.

3. Silk.

4. Wool.

Flax is a much better conductor than cotton; cotton is a somewhat better, but not much better, conductor than silk; silk is a much better conductor of heat than wool. It may prove to be at once more succinct and more useful, to name the raw materials of the several articles of clothing in this way, than to attempt an enumeration of the several fabrics individually. It is sufficiently easy to estimate the comparative warmth and protection to be expected from any article of clothing, by knowing the material or materials of which it is manufactured. Thus, all woollens, as cloths, worsteds, stuffs, merinoes, &c., are warmer articles of wear, than silks, spun silks, &c.; and these, than calicoes, common prints, &c.; and these, than linens, muslins, cambrics, &c.

It is necessary to add to these four principal raw materials of manufacture, some few other articles, which are more or less directly used to protect the surface of the body from the cold. Thus, feathers

are bad conductors; and, à fortiori, down is pre-eminently a bad conductor. The quilt lined with Eider down, is, from its extreme lightness and remarkably non-conducting property, a priceless comfort to the easily chilled surface of the invalid. Hair, when woven into a cloth, is rather a good conductor; but in the state of fur, is a very bad conductor. Wood, and more especially cork, is a very bad conductor. Leather and dressed skins are bad conductors, and might probably be classed as little less so than wool.

The position that articles made of silk should occupy in such a comparative estimate of the degree of protection afforded to the surface of the body, would be necessarily affected a good deal by the degree of thickness or thinness of the manufactured fabric. The greater costliness of the raw material, makes this a consideration of more importance in the case of this, than in that of the other fabrics. has, moreover, another physical characteristic, which adapts it pre-eminently to be an important article of clothing. It is singularly notable as a non-conductor of electricity.

Silk

However little or unsatisfactory our knowledge of the operations of this remarkable agent in the animal economy, there is no doubt that electricity fulfils important and necessary purposes in the living system, and that a certain amount of positive or negative electricity is being constantly given off from the surface of the body, in greater or less degree, according to sex, temperament, weather, the nature of the clothing, &c. It has been said, that the skin