While your body is alive, there is a hard frame-work inside of it, upon which the soft flesh is fixed, in order that it may be kept in a convenient and durable form, and around which the water is packed in a countless myriad of chambers, and vessels, and porous fibres. The hard internal frame-work is composed of what are called bones. In the dried mummy, left when the moisture is all gone from the body, there are rather more than nine pounds of this mineral bone-substance. But there are also nearly three-quarters of a pound of other mineral substances, which were scattered about in various situations, and which were employed for various purposes. There is salt which was in the saliva, in the gristle, and in the blood. There is flint which was in the hair. There is iron which was in the blood. There is potash which was mixed with the flesh-substance. There are lime and phosphorus in the hard millstones—the teeth; and there is phosphorus, which was in the nerves and the brain. These mineral substances with the bone-earth, which is principally a kind of lime, form together the ash or dust which is returned to the ground after the body has decayed. It is the flesh-substance which flies away to become poison-vapor in the air. But besides water to do transporting work, flesh substance to do active mechanical or moving work, and mineral substance to do passive mechanical or supporting work, there is yet another kind of material within the body. You have as much as six pounds of fat, scattered about or packed away amid the seventeen pounds of dry flesh. What can that be for? What use do you think you make of your fat? You have, I dare say, a sort of comfortable sense that it keeps you warm. You know that some of your lean neighbors cast envious eyes towards you in severe winter weather, and have chattering teeth and goose’s skins, when you are quite free from such tokens of chilliness. But you will nevertheless be surprised when I tell you what a really fiery piece of business this warming by fat is. Your fat is a store of fuel, which you are going to burn to heat your body, exactly as you burn coal in the grate to heat your room in the winter. It is oil laid by, to be consumed gradually, as a sort of liquid coal, in the furnace of the living machine. Of this, we shall, however, have to say more, by itself, by and by. For the present merely bear in mind that fat is the fuel substance which furnishes warmth to the body. It also combines with the phosphorus and with water to make up the nerve-substance and the brain-substance, which do the feeling and thinking work. These too, however, will have to be spoken of hereafter by themselves. Let us now then take stock of the stores we have on hand, within the skin of a living body of 150 pounds weight. We have