Now the very possibility of such a material organism as this depends upon a highly complex form of matter termed protoplasm, which is at once extremely plastic and of extreme instability, and is yet capable of secreting or building up its atoms into such solid and apparently durable forms as bone, horn, and hair, besides the various liquids and semi-solids which build up the organism. This fundamental organic substance consists of only four chemical elements--nitrogen, hydrogen, oxygen and carbon, and almost all animal and vegetable structures and products have the same elemental constitution, though with such widely different characteristics. Four other elements--sulphur, lime, silicon, and phosphorus--also occur in small quantities in organic tissues, to supply special needs; but these are not essential to all forms of life, and are only taken up and utilised by the living protoplasm when required. Protoplasm is undoubtedly the basis of physical life, yet it only exists in, and is produced by, living organisms. The moment such an organism dies, disorganisation and decay set in, and the whole mass becomes gradually changed into more stable compounds, or into its constituent elements. It appears, therefore, that some agency--usually termed “vital force”--must be at work, first to produce this wonderful compound, then to form it into “cells”--the physiological units of all organisms--and afterwards to direct the energies supplied by heat and light so as to build up the excessively complex structures, with all their wonderful powers and potentialities, which we term animals and plants. All this seems to imply not “a force” only, but very many forces, all of which must have some kind of mind in or behind them, to direct these forces to such infinitely varied yet perfectly defined ends. [Sidenote: A Marvel of Every Day]