Now, it is supposed that, in the beginning of the world, there was, in space, such a nebula or mass of incandescent vapour, which, as it was destined to cool down and form a world, philosophers have called “cosmic gas.”

This cosmic gas, in the course of time, began to lose its heat, and consequently to liquefy and solidify, according to the different nature of its components; and thus a globe with a solid crust was formed, the surface of which was partly dry and partly occupied by water, and diversified by the abundant production of the various earths, gases, metals, and other substances with which we are familiar.  These substances, in time, and by the slow action of their own laws and properties, combined or separated and produced further forms.  But to come at once to the important part of the theory, we must at once direct our attention to four substances; these would certainly, it is said (and that no doubt is quite true) be present; they are oxygen, hydrogen, nitrogen, and carbon.  The first three would be, when the earth assumed anything like its present conditions of temperature and air-pressure, invisible gases, as they are at present; the fourth is a substance which forms the basis of charcoal, and which we see in a nearly pure form crystallized in the diamond.

Now, if these substances are brought together under certain appropriate conditions, the oxygen and hydrogen can combine to form water; the carbon and the oxygen will form carbonic acid; while nitrogen will join with hydrogen to form that pungent smelling substance with which we are familiar as ammonia.  Again, let us suppose that three compound substances—­water, carbonic acid, and ammonia—­are present together with appropriate conditions; it is said that they will combine to form a gummy transparent matter, which is called protoplasm.  This protoplasm may be found in small shapeless lumps, or it may be found enclosed in cells, and in various beautifully shaped coverings, and it is also found in the blood, and in all growing parts or organs of all animals and plants of every kind whatsoever.

Protoplasm, then, is the physical basis of life.  Simple, uniform, shapeless protoplasm, combined out of the substances just named, first came into existence; and as, however simple or shapeless, it always exhibits the property of life, it can henceforth grow and develop from simpler to ever increasingly complex forms, without any help but that of surrounding circumstances—­the secondary causes which we see in operation around us.

If some readers should say they have never seen protoplasm, I may remind them where every one has, at some time or another, met with it.  If you cut a stick of new wood from a hedge, and peel off the young bark, you know that the bark comes off easily and entire, leaving a clean white wand of wood in your hand; but the wand feels sticky all over.  This sticky stuff is nothing more than transparent growing protoplasm, which lies close under the inner bark.