The cell is the first step in the specialisation of protoplasm, the outer layer of which, in contact with the surrounding environment, becoming hardened so as to form an enclosing cell-wall, while a portion of the enclosed protoplasm condenses into a nucleus, in which a further condensation makes what is called the nucleolus or second smaller nucleus. This constitutes the nucleated cell, whose repeated subdivision into other similar cells in geometrical progression furnishes the raw material out of which all the varied structures of the world of life are built up. Plants and animals, bones, muscles, and organs of sense, are all composed of modified cells, hardened, flattened, or otherwise altered, as the case may require. If we trace life up to its origin in the individual instead of in the species, we arrive at the same result. All plants and animals, whether of the lowest or highest forms, fish, reptile, bird, mammal, man, begin their individual existence as a speck of protoplasm, passing into a nucleated cell, which contains in it the whole principle of its subsequent evolution into the mature and completed form. Protoplasm is, therefore, evidently the nearest approach of life to matter; and if life ever originated from atomic and molecular combinations, it was in this form. To suppose that any more complex form of life, however humble, could originate from chemical combinations, would be a violation of the law of evolution, which shows a uniform development from the simple to the complex, and never a sudden jump passing at a bound over intermediate grades. To understand life, therefore, we must understand protoplasm; for protoplasm, closely as it approximates to colloid matter, is thoroughly alive. A whole family, the Monera, consist simply of a living globule of jelly, which has not even begun to be differentiated. Every molecule, as in a crystal, is of homogeneous chemical composition and an epitome of the whole mass. There are no special parts, no organs told off for particular functions, and yet all life-functions—nutrition, reproduction, sensation, and movement—are performed, but each by the whole body. The jelly-speck becomes a mouth to swallow, and turning inside out, a stomach to digest. It shoots out tongues of jelly to move and feel with, and presently withdraws them. With these attributes it is impossible to deny to protoplasm the full attributes of life, or to doubt that, like the atom in the material world, it is the primary element of organic or living existence. Given the atom, we can trace up, step by step, the whole evolution of matter; so given the protoplasm, we can trace up the evolution of life by progressive stages to its highest development—man. To understand life, therefore, we must begin by trying to understand protoplasm.