The old methods of enquiry and thought which Hegel terms metaphysics, which by preference busied themselves by enquiring into things as given and established quantities, and the vestiges of which still buzz in the heads of people, had at that time great historical justification. Things had first to be examined, before it was possible to examine processes; man must first know what a thing was before he could examine the preceding changes in it. And so it was with natural science. The old metaphysic which comprehended things as stable came from a philosophy which enquired into dead and living things as things comprehended as stable. But when this enquiry had so far progressed that the decisive step was possible, namely, the systematic examination of the preceding changes in those things going on in nature itself, then occurred the death-blow of the old metaphysics in the realm of philosophy. And, in fact, if science to the end of the last century was chiefly a collecting of knowledge, the science of actual things, so is science in our day pre-eminently an arranging of knowledge, the science of changes, of the origin and progress of things, and the mutual connection which binds these changes in nature into one great whole. Physiology, which examines the earlier forms of plant and animal organisms; embryology, which deals with the development of the elementary organism from germ to maturity; geology, which investigates the gradual formation of the earth's crust, are all the products of our century.