Everything that has sensation lives. As life depends upon particular combinations of particular elements, so sensation is the characteristic mark of such combinations, and a higher form of that simple reaction common to nature in general. Reaction has its reason in the motion arising from the endless divisibility of matter, through which the most different combinations and reactions are produced. Since we have before us, in our contemplation of corporeal nature, not abstract matter in general, but some sixty or more special chemical elements, we must, in thinking of atoms, have in mind atoms of these particular elements, and not atoms of abstract matter in general; of such atoms of matter in general, or, if one will, of primordial matter, we can know only that they would in general attract and repel. Only by degrees can a particular reaction of the elements have been developed; and since our known elements have particular different reactions, they must be the product of different combinations. Sensation is due to certain combinations of these elements; when the combinations no longer exist, the atoms of these elements still react according to their characteristic method as atoms of particular elements, but the sensation dependent on their peculiar combinations is destroyed. The atom as such is devoid of sensation, and we may convert our earlier proposition, making it read: Only that which lives is sensible. We know quite well how much of this course of reasoning is of hypothetic nature; but the strictest consistency cannot be denied it. The method which explains life by the assumption of sensible atoms is a much shorter and easier one; but is it not likewise a method of greater risk? And is there no danger that, in rejecting a method by which all changes in phenomena are referred to functions of combinations of elements, we may seek, in matter itself, something that is not matter? The above theory of life, also, takes its departure from the assumption that all was, originally, in the formation of the world, living in the broader sense of the word. But here we are concerned with life in the narrower sense of the word, as distinguished from what we call dead nature.