Besides the bowels, there are several other channels by which the waste materials of the body pass out. The most important of these are the skin, the lungs, and the kidneys; and in certain circumstances, where the action of the one is impaired or repressed, the natural alliance subsisting among their respective functions, enables the rest to come to its assistance, and even for a time to supply its place. Thus, when, by continued exposure to cold, the exhalation from the skin is much diminished, the blood is thrown in upon the internal organs in larger quantity, and, as a consequence, the urinary secretion and the exhalation from the lungs are both increased, and full relief to the system is temporarily obtained. During hot weather, on the other hand, when the skin is in high action, and perspiration flowing freely, the urinary secretion is greatly lessened. The same principle applies equally to the case of the bowels; and hence the sudden application of cold to the surface of the body, and consequent suppression of perspiration, often increase the intestinal secretions to such an amount as to induce bowel-complaint. On the other hand, the excited action of the bowels by laxatives, tends equally to diminish the activity of the skin; and hence, indeed, one source of the _cooling_ effect of saline purgatives administered in fever and inflammations. The bowels being thus the outlet of the indigestible portion of the food, and of waste matter from the system, it follows that, in health, their action ought to bear a relation to the kind of aliment used, and to the state of the other excretory functions; and consequently, that what may constitute healthy action at one time, and in one individual, may be very far from presenting the same character at another time, and in a different individual. If, for example, a person be fed chiefly on milk, rice, or farinaceous aliment, which is almost entirely appropriated to the purposes of nutrition, and leaves very little residue, the bowels, having little to throw out, will naturally act seldomer and less fully than when the diet consists chiefly of bulky and innutritious vegetables, which leave a large portion of indigestible matter to be evacuated. Most persons are aware of the difference of effect between the two kinds of diet, but, from not being acquainted with the principle on which it depends, are apt to conclude that, because in the first case the bowels act less, therefore they ought to be assisted by laxatives. The inference, however, is by no means necessarily sound; because the diminished intestinal action consequent on an exclusively farinaceous diet is then the natural and healthy result; and accordingly, _where such diet is required_, the mere costiveness is attended with no injury to the constitution. The proper conclusion to be drawn from it is, that the permanent and exclusive use of concentrated food is not in harmony with the structure