Or, if it be a reaction by means of which energy is set free, it occurs spontaneously. No energy is absorbed in setting it going. All the energy liberated is effective. The chemist very frequently needs to heat a substance in order to cause it to decompose, even though it be falling from a less stable to a more stable state. Vital chemistry and mineral chemistry are so widely different in their methods that one is tempted to think of them as different in kind. We find it very difficult to look at both from the same point of view. Men’s minds are preoccupied with the things that they have to do for themselves. The chemistry of the laboratory is seen as a science circumscribed by the laboratory walls. If it were possible to stand outside, it would be evident that it is only a part of the science of molecular change. Matter changes its state under the influence of force. Many rearrangements are effected by the chemist which do not occur in nature. He has an almost infinite range of action. Yet many of the rearrangements of matter and force which are occurring in the dandelion on his window-sill (if the fumes of sulphuretted hydrogen have not killed it) he is unable to reproduce. It is largely a question of waste. Nature works with greater precision than the chemist; but the chemist could do all that Nature does if he had but the same control of force. We have spoken of the reactions which occur in protoplasm as divisible into two great series—the one ascending, constructive, endothermal; the other descending, destructive, exothermal. In the one series energy is locked up; in the other series it is set free. Synthesis and analysis are names applied to the two series respectively. Synthesis is characteristic of plants, although analysis is also perpetually occurring. Plants fix carbon from the air and liberate oxygen. They also respire, setting free carbonic acid. Analysis is characteristic of animals, although synthesis is not excluded.