Nor can the intelligent reader be unaware that the nutrient portion of the food we eat, after undergoing the process of digestion performed in the mouth--where it is masticated and mingled with the solvent saliva-- in the stomach, where it is reduced by muscular action, and the gastric juices to the pulp called chyme--in the upper portions of the intestines--where it receives the secretions of liver and pancreas and becomes chyle, is collected by a series of absorbent vessels which unite at last to form the thoracic duct, or grand chyle canal, which empties itself of its valuable contents directly into one of the largest veins in the body, and is thus mingled with the general circulation. He knows, too, that the pure life-giving arterial blood, which, rushing onwards from that mighty force-pump, the heart, is distributed to every atom of the system, returns at last laden with the used up particles of the tissues; that, in fact, a constant change is going on in the system, a constant deposit of new matter, a constant discharge of old. And that the dark venous blood, containing the effete matter, rushes through the lungs, therein to be spread out, and chemically united to the oxygen of the air that we breathe, before it is again pumped out towards the tissues to supply them with heat and life. But it must not be forgotten, that not the lungs only, but the kidneys, the liver, and the spleen have each and all of them their duties to perform towards the blood; and last, but not least, that the skin, when in a state of health, assists them in no small degree in performing their several functions. But there are other glands which receive assistance from the skin in the performance of their duties. We refer to those distributed here and there in the frame-work of the body, notably in the axilla, the groin, and under the skin of the neck, and whose functions are to purify, in some way or other, the matter collected by a series of vessels called the lymphatics, before it is again applied to the purposes of nutrition. "The amount of fluid," says a well-known physiologist, "exhaled from the skin and lungs in twenty-four hours, averages about three or four pounds. And there is good reason to think that this excretion is of the greatest importance in carrying off certain substances that would prove injurious if allowed to remain in the blood. "That which is called the Hydrophatic system, proceeds upon the plan of increasing the cutaneous exhalation to a very large amount; and there seems much evidence that certain deleterious matters, the presence of which in the blood gives rise to gout, rheumatism, etc, are drawn off from it more speedily and certainly in this way than in any other." If space permitted, the utility of the skin as one of the greatest emunctories of the system might be much enlarged upon; we trust, however, we have said quite enough to establish its importance in the animal economy. CHAPTER TWO.