1. Each organism is characterized by a definite form and we shall see in the next chapter that this form is determined by definite chemical substances. The same is true for crystals, where substance and form are definitely connected and there are further analogies between organisms and crystals. Crystals can grow in a proper solution, and can regenerate their form in such a solution when broken or injured; it is even possible to prevent or retard the formation of crystals in a supersaturated solution by preventing “germs” in the air from getting into the solution, an observation which was later utilized by Schroeder and Pasteur in their experiments on spontaneous generation. However, the analogies between a living organism and a crystal are merely superficial and it is by pointing out the fundamental differences between the behaviour of crystals and that of living organisms that we can best understand the specific difference between non-living and living matter. It is true that a crystal can grow, but it will do so only in a supersaturated solution of its own substance. Just the reverse is true for living organisms. In order to make bacteria or the cells of our body grow, solutions of the split products of the substances composing them and not the substances themselves must be available to the cells; second, these solutions must not be supersaturated, on the contrary, they must be dilute; and third, growth leads in living organisms to cell division as soon as the mass of the cell reaches a certain limit. This process of cell division cannot be claimed even metaphorically to exist in a crystal. A correct appreciation of these facts will give us an insight into the specific difference between non-living and living matter. The formation of living matter consists in the synthesis of the proteins, nucleins, fats, and carbohydrates of the cells, from the split products. To give an historical example, Pasteur showed that yeast cells and other fungi could be raised on the following sterilized solution: water, 100 gm., crystallized sugar, 10 gm., ammonium tartrate, 0.2 gm. to 0.5 gm., and fused ash from yeast, 0.1 gm.[7] He undertook this experiment to disprove the idea that protein or organic matter in a state of decomposition was needed for the origin of new organisms as the defenders of the idea of spontaneous generation had maintained. [7] Pasteur, L., _Annal. d. Chim. et d. Physique_, 1862, 3 sér., lxiv., 1.