Whether or not these so-called elements are really true elementary forms of matter, which are absolutely indivisible, is a problem for the chemists of the coming centuries to solve. The classification has the approval of the present age. What new elements may be found no one may predict. Mendelejeff’s _periodic law_, however, suggests great possibilities in this field. Allotropism, in which the same element will present entirely different physical aspects, is also a significant and suggestive phenomenon, for in it we see carbon appearing at one time as a crude, black and ungainly mass of coal, and at another it appears as the limpid and flashing diamond. In more than one mind there is a lurking suspicion that there may, after all, be only one form of primordial matter, from which all others are derived by some wondrous play of the atoms, and if so the old idea of the alchemist as to the transmutation of metals may not be entirely wrong. The Twentieth Century may give us more light. CHAPTER XIX. FOOD AND DRINK. THE NATURE OF FOOD--THE ROLLER MILL--THE MIDDLINGS PURIFIER-- CULINARY UTENSILS--BREAD MACHINERY--DAIRY APPLIANCES--CENTRIFUGAL MILK SKIMMER--THE CANNING INDUSTRY--STERILIZATION--BUTCHERING AND DRESSING MEATS--OLEOMARGARINE--MANUFACTURE OF SUGAR--THE VACUUM PAN--CENTRIFUGAL FILTER--MODERN DIETETICS AND PATENTED FOODS. If called upon to name the most important of all factors of human existence, that which underlies and sustains all others, even to life itself, everyone must agree that it is _food_. A remarkable fact in this connection is that all animal life lives and thrives by eating some other thing that is or has been alive, or is the product of organic growth. The vegetarian may pride himself upon his higher ideals of living, but after all his fruit, vegetables, and cereals belong to the great category of living organisms, and are to a certain extent sentient and conscious, for even the plant will turn to the sun. The beasts of the field and fowls of the air live by preying upon other weaker animals and birds, these upon plants and grasses, and the plants and grasses upon the decaying mosses and organic mould of the soil, and the mosses upon still lower organisms. The big fish of the sea eat the little fish, the little fish the small fry, and these in turn live upon worms and animalcula, and so on all the way down to protoplasm. Omniverous man, in spite of his boasted civilization and enlightment, not only eats them all, flesh, fowl, fish, grain and plants, but lives exclusively upon them. But he can _only_ live on that which has been produced by the mysterious agency of life, and this furnishes a significant suggestion for the philosopher, for it may be that life itself is only an accumulated active power or unitary force regenerated in some metamorphic way from vital force stored up in the bacteria of organic food, and necessarily connected therewith in an endless chain of