The Wastes of the Body. Almost everything that the body does in the process of living means the breaking down, or burning, of food; and produces, like every other kind of burning, two kinds of waste--"smoke" and "ashes." The carbon dioxid "smoke," as we have already learned, is carried in the blood to the lungs, where it passes off in the breath. The solid part of our body waste, or the "ashes," is of two kinds--that which can be melted in water, or is, as we say, _soluble_; and that which cannot be melted in water, or is _insoluble_. The insoluble part of our solid body waste goes into the feces and is thus disposed of. The soluble part of the body waste goes by a somewhat more roundabout route. With the carbon dioxid it is poured by the body cells into the veins, carried to the heart, and pumped through the lungs, where the carbon dioxid is thrown off. Going back to the heart it is pumped all over the body, part of it going through a very large artery to the liver, part through two large arteries to the kidneys, part to the skin, and the rest all over the remainder of the body. The blood goes completely round the body-circuit from the heart to the fingers and toes, and back again to the heart, in less than forty-five seconds. Practically every drop of blood in the body will be pumped through the liver, the kidneys, and the skin, about once every half minute, so that they get plenty of chance to purify it thoroughly when they are working properly. This sounds rather complicated; but is interesting, because it shows how much of a "mind of their own" the different organs and stuffs in our bodies have, or what, in scientific language, we call "power of selection." The skin glands pick out of the blood those waste substances which they are able to get rid of. The kidneys pick out another class of waste substances, which they are best able to deal with; while the liver which is the most important of all, attacks almost every kind of waste brought to it by the blood, and prepares it for disposal by the intestines, skin, and kidneys. The Liver. The liver has a size to match its importance. It is the largest and heaviest gland, or organ, in the body, and weighs about three pounds, a little more than the brain. It buds off from the food tube just below the stomach, so that its waste tube, the _bile duct_--about the size of a goose quill--opens into the upper part of the intestine. The main work of the liver is to receive the blood from all over the body and to act upon its waste substances, burning them up so that they can be taken up, and got rid of, by the glands of the skin and the kidneys. In the process it very frequently changes these waste substances from poisonous into harmless forms; and even when disease germs get into the body and infect it, the poisons, or toxins, which they pour into the blood are carried to the liver and there usually burned up, or turned into harmless substances.