Oxidation may be said to be the basis of all life processes for this reason: oxidation gives rise to heat and sets free energy, and all living things need heat and energy in order to grow and live. The heat of animals is very noticeable. The oxidation in plants also forms a slight amount of heat. In both animals and plants oxidation is much slower than in ordinary fires. That heat is formed even in slow oxidation is shown by fires which arise spontaneously in masses of decaying material. The rotting of wood is not only accompanied by heat but sometimes by light, as when “fox fire” is emitted. Rub the end of a match on your finger in the dark. Explain the result. Strike a match and notice the white fumes which rise for an instant. These fumes are not ordinary smoke (particles of carbon), but they are oxid of phosphorus. Why will water (oxid of hydrogen) not burn? Sand is oxid of silicon. Explain how throwing sand on a fire puts it out. [See also experiments with candle and breath, in The Principles of Biology.] =Inorganic and Organic Matter.=--=Test for Minerals.=--The earth was once in a molten condition, which would have destroyed any combustible material if any had then existed. Before plants and animals existed, the earth consisted mostly of incombustible minerals, known as _inorganic matter_. Substances formed by animals and plants are _organic matter_, so called because built up by organized or organ-bearing or living things; starch is an example, being formed in plants. Organic substances are composed chiefly of carbon, oxygen, hydrogen, and nitrogen. (See page 1 of “Animal Biology.”) Coal-oil, and all combustible materials have their origin in life. Hence, burning to find whether there is an incombustible residue is also a _test for minerals_. Meat, bread, oatmeal, bone, wood, may be tested for mineral matter by burning in a spoon held over a hot fire, or flame of gas or lamp. The substance being tested should be burned until all black material (which is organic carbon and not a mineral) has disappeared. Any residue will be _mineral matter_. =Protoplasm.=--Inside the cells of plants and animals is the _living substance_, known as _protoplasm_. It is a structureless, nearly or quite colorless, transparent jelly-like substance of very complex and unstable composition. Eighty per cent or more is water; the remainder is proteid, fats, oils, sugars, and salts. Protoplasm has the power of _growth and reproduction_; it can make _living substance from dead or lifeless substances_. It has the _power of movement_ within the cell, and it is influenced (or is irritable) by heat, light, touch, and other stimuli. When protoplasm dies the organism dies. =Physics= is the science that treats of the _properties_ and _phenomena_ (or behavior) of matter or of objects; as of such properties or phenomena or agencies as heat, light, force, electricity, sound, friction, density, weight, and the like.