Since then these investigations into protoplasmic sensibility have been pursued with much ardour among micro-organisms. These beings, sometimes animal, sometimes vegetable, are simple masses of protoplasm, generally monocellular, appearing homogeneous, without differentiation of tissues. Now very varied _tendencies_ have been found among these organisms. Some seek light, others flee from it persistently. The protoplasmic mass of myxomycetes which live in the bark of the oak, if placed in a watch-glass full of water, remain there in repose; but if sawdust is placed around them they immediately emigrate towards it as if seized by home-sickness. The actynophrys acts in the same way with regard to starch. Bacteria can discover even the trillionth part of a milligram of oxygen in a neighbouring body. Certain sedentary ciliated creatures appear to choose their food. Some also have thought that they detected an elective tendency in the movement which draws the male ovule towards the female ovule. I have only recalled a few of the many facts which have been enumerated. If it is necessary to mention other examples, I may refer to the case studied in our own days under the name of “phagocytosis.” The struggle for life goes on, not only among individuals, but also among the anatomical elements which constitute the individual. Every tissue—muscular, connective, adipose, etc.—possesses phagocytes (devouring cells), of which the duty consists in devouring and destroying old or enfeebled cells of the same kind. Besides these special phagocytes there are general phagocytes, such as the white corpuscles of the blood, which come to the help of the others when they are not equal to their task. They stand against the pathogenic microbes, waging upon them an internal struggle, and opposing the invasion of infectious germs. This apparently teleological property seems at first very surprising. Later investigations have shown that the phagocytes are endowed with a sensibility (called chemiotaxic), owing to which they are able to distinguish the chemical composition of their environment and to approach it or leave it accordingly; deteriorated tissues attract certain of them which incorporate the feeble or dead cells, while the healthy and vigorous elements are perhaps able to defend themselves by secreting some substance which preserves them from phagocytosis. These facts, taken from among many others to which I shall again have to refer when dealing with the sexual instinct, have been interpreted in two very different ways: one psychological, the other chemical. For some there is in all these phenomena a rudiment of consciousness. Since the movements are adapted and appropriate, varying according to circumstances, there must be choice they say, and choice involves a psychic element; the mobility is the revelation of an obscure “psyche” endowed with attractive and repulsive tendencies.