Although the law just referred to about the permanence and the mutability of physical forces thus seems rather to disprove materialism, it was not for this reason chiefly that we have related it. Our purpose is to find a basis in this fact from which the fundamental contrariety between organic and inorganic matter most easily may be explained, and thereafter to enter into this differentiation just as far as is necessary to decide the main point as to whether one form of matter can spontaneously produce another. We recollect that the materialists endeavored to make the difference between organic and inorganic compounds as slight as possible. The former consisted of exactly the same elements as the latter and these elements had exactly the same qualities in one compound as in another. However true this may be, is not meat nevertheless something different from limestone, although limestone may easily be found that contains nearly all the elements present in the meat? In starch, sugar, fat, etc., precisely the same elements enter as in water and carbonic acid, but no materialist denies that there are important differences between these two groups of substances. What is it, then, that essentially separates the two classes of matter (nothing but the most essential factors concerns us here)? If we ask this question of chemistry, we are answered that this quality is combustibility. Organic matter is combustible; inorganic is not. But why should organic matter be combustible? Because fuel is as necessary to the organism as to the steam engine. To both their physical source of power is heat, and even the engine receives it through the combustion of organic substances. All the fuel that is generally used is of organic origin, although we seldom think of this fact. But why can we not fire an engine with inorganic products? Because these cannot burn, and the reason again is, that they are already burned. If this be true, they must once have been fuel themselves, must once have been in a burning state. How do we know this? Because the inorganic world consists almost entirely of chemical compounds that are only formed by combustion, when this word is used in its widest sense. If these suggestions are correct, organic matter is to inorganic as fuel to the products of combustion. In the inorganic world the latter have been transformed to fuel which in a renewed combustion reproduces the same products as those of which it once was formed. If this be the case our problem may be thus formulated: Can inorganic products of combustion again form combustibles spontaneously? Can carbonic acid or water through the _spontaneous activity of physical forces_ be transformed into sugar, starch, fat, etc.? In order to decide if this be possible we must first know what combustion is, and we will therefore briefly explain what this term means.