So, too, in the corporate life of the individual man it is the association of the nerve cells, their lines of connection and communication, that is responsible for the most of the differences between the ignorant and the educated, the savage and civilized man. The neurone, however, is a little unicellular animal, like the amoeba or the paramecium. Its life consists of: (1) eating, (2) excreting waste products, (3) growing, (4) being sensitive, and (5) movement, and, as Thorndike expresses it: "The safest provisional hypothesis about the action of the neurones singly is that they retain the modes of behavior common to unicellular animals, so far as consistent with the special conditions of their life as an element of man's nervous system." In the widest sense of the term, behavior may be said to include all the chemical and physical changes that go on inside the organism, as well as every response to stimulus either from within or from without the organism. In recent studies of animal behavior, however, the word has acquired a special and technical meaning in which it is applied exclusively to those actions that have been, or may be, modified by conscious experience. What the animal does in its efforts to find food is behavior, but the processes of digestion are relegated to another field of observation, namely, physiology. In all the forms of behavior thus far referred to, human and animal nature are not fundamentally distinguished. There are, however, ways of acting that are peculiar to human nature, forms of behavior that man does not share with the lower animals. One thing which seems to distinguish man from the brute is self-consciousness. One of the consequences of intercourse, as it exists among human beings, is that they are led to reflect upon their own impulses and motives for action, to set up standards by which they seek to govern themselves. The clock is such a standard. We all know from experience that time moves more slowly on dull days, when there is nothing doing, than in moments of excitement. On the other hand, when life is active and stirring, time flies. The clock standardizes our subjective tempos and we control ourselves by the clock. An animal never looks at the clock and this is typical of the different ways in which human beings and animals behave. Human beings, so far as we have yet been able to learn, are the only creatures who habitually pass judgment upon their own actions, or who think of them as right or wrong. When these thoughts about our actions or the actions of others get themselves formulated and expressed they react back upon and control us. That is one reason we hang mottoes on the wall. That is why one sees on the desk of a busy man the legend "Do it now!" The brutes do not know these devices. They do not need them perhaps. They have no aim in life. They do not work.