We have spoken of Air and Water, in a former chapter, and their constituent atoms have been named. And from these three great reservoirs of Substance--the Earth, the Air, and the Water--are obtained all the material that goes to form the bodies of the animal and vegetable kingdoms. The plant draws its nourishment from the soil, the air, and water, and in its wonderful chemical laboratory is able to transform the elements so drawn from these sources into a substance called "Plasm," which consists principally of carbon, oxygen, nitrogen and hydrogen, being nearly identical in composition to the white of an egg, and which constitutes the basis of animal and plant bodily structures. All the material of the physical bodies, of men, animals and plants, are but forms of Plasm. The animals, and man, obtain their nourishment, directly or indirectly, from the plant body, and so at the last we are seen to draw from the soil, air and water all our bodily nourishment, which we convert into bodily structure, bone, muscle, flesh, blood, veins, tissue, cells, etc. And the chemical atoms of our bodies are identical with those in the rock, the air, the water. And so you see the universality of Substance and its countless forms and appearances. Chemistry resolves Substance back into about seventy-five simple substances, of which Atoms are the Units, which simple substances are called "Elements." From these Elements (by their Atoms) all other substances are formed by combinations, the number of such possible combinations being infinite. An Element (in order to be an element) must be a "simple" substance, that is, must be incapable of further analysis into some other elements. The seventy-five elements, now recognized by science, have never been resolved into other elements, by chemical analysis, and therefore are accepted as "simple." But, it is true that other substances that were formerly considered as simple elements were afterward decomposed by electricity, and found to consist of two or more simpler substances or elements. Thus new elements were discovered, and old ones discarded as "not-elemental." And this fate may be in store for a number of the elements now on the list--and many new ones may be discovered. For a long time Science was endeavoring to trace all elements back to Hydrogen, the latter being considered the "Ultimate Element," and its atoms composing all the other atoms, under varying conditions, etc. But this theory is now almost abandoned, and Science rests on its list of seventy-five elements, the atoms of which are composed of "Electrons." Some have hazarded the theory that the Elements were all forms of Ether (see next chapter), their apparent differences resulting merely from the varying rate of vibration, etc. And, in fact, such theory was about finally adopted as a working hypothesis until the discovery of the Corpuscle. Everything in Substance now seems to be moving back to the Corpuscle, as we shall see a little further on.