When man began first to think of the material composition of his body, he naturally assumed it to be composed of special and very precious materials. The science of chemistry has, however, step by step brushed away the superstitions of the mythol-ogists and the mysteries of the alchemist, and revealed the fact that man's body is composed of the most ordinary elements, such as carbon, oxygen, hydrogen, nitrogen, phosphorus, sulphur, chlo-rin, sodium, potassium, magnesium, iron, and calcium. These elements will be recognized as the most widely distributed substances in nature. Carbon combined with oxygen, as carbon dioxid, makes an appreciable proportion of the earth atmosphere; oxygen itself makes about one fifth of the atmosphere, while nitrogen makes nearly four fifths. Hydrogen combined with oxygen in water is practically universal in its distribution, appearing on the surface of the earth, in seas, lakes, and rivers, forming great underground streams and strata in the surface rocks and soils of the earth, and floating in clouds, fogs, and vapors in the atmosphere. Those rocks which contain calcium, iron, magnesium, sodium, and potassium are most universal in their distribution. So we find that these substances of which man is constructed are universally distributed over the surface of the earth.

But man is not alone in the use of these widely distributed substances in his body. All living things on the earth, whether plants or animals, are constructed of these twelve substances.

Living things may be said to be made of the dust of the earth.

The questions that first come to the thoughtful mind are: What is the essential difference between living things and non-living things? What is the difference between a stalk of corn and the soil from which it grew? What is the difference between a clam and the mud in which it lives? What is the difference between a man and the rock on which he stands? A study of the chemical composition of the living and the non-living shows that the difference does not exist in the elements of which they are composed, but in the complexity of combination of these elements. The growing stalk of corn is composed of cellulose, chlorophyll, sugar, woody fiber, which represent complex combinations of carbon, hydrogen, nitrogen, oxygen, phosphorus, sulphur, chlorin, iron, potassium, calcium, and magnesia, while the soil and air in which the corn grew is composed of water (H20), carbon dioxid (CO2), calcium carbonate (CaCO3), nitrates (as NaNO3 or KNO3), phosphates (as CaHPO4), chlorids (as MgCL), sulphates (as CaSO4), together with many other simple compounds. Note that even the more complex molecules in the soil contain only a few atoms, while one of the simpler molecules in the corn is cane sugar (C12H22O11), which contains forty-five atoms. Some of the more complex molecules of a growing stalk of corn represent probably not fewer than two or three thousand atoms. One may, therefore, sum up as follows:

The body is composed of twelve universally distributed elements (C, H, N, O, P, S, Cl, Na, K, Mg, Fe, Ca) combined in the most complex molecules, some of which contain many hundreds, even thousands, of atoms.