The fact that a boy is a boy makes him heir to all of the characteristics that man has developed. These characteristics are his birthright. He responds in a particular way to stimuli because the race before him has so responded. There is no need here of entering into a discussion as to how great a controlling factor heredity may be in a man's life, or how potent environment may be in modifying that life--we are concerned rather with the result--that man is as he is. It is essential that we know his characteristics, particularly as they manifest themselves in youth, so that we may know what to expect in his conduct and so that we may proceed to modify and control that conduct. Just as the first task of the physician is to diagnose his case--to get at the cause of the difficulty before he proceeds to suggest a remedy--so the first consideration of the teacher is a query, "Whom do I teach?" Man may normally be expected to respond in a particular way to a particular stimulus because men throughout the history of the race have so responded. Certain connections have been established in his nervous system and he acts accordingly--he does what he does because he is _man_. We cannot here go into a detailed discussion of the physiological processes involved in thinking and other forms of behavior, but perhaps we may well set down a statement or two relative to man's tendencies to act, and their explanations: "The nervous system is composed of neurones of three types: Those that receive, the afferent; those that effect action, the efferent; and those that connect, the associative. The meeting places of these neurones are the synapses. All neurones have the three characteristics of sensitivity, conductivity, and modifiability. In order for conduct or feeling or intellect to be present, at least two neurones must be active, and in all but a few of the human activities many more are involved. The possibility of conduct or intelligence depends upon the connections at the synapses,--upon the possibility of the current affecting neurones in a certain definite way. The possession of an 'original nature,' then, means the possession, as a matter of inheritance, of certain connections between neurones, the possession of certain synapses which are in functional contact and across which a current may pass merely as a matter of structure. Just why certain synapses should be thus connected is the whole question of heredity. Two factors seem to affect the functional contact of a synapses,--first, proximity of the neurone ends, and second, some sort of permeability which makes a current travel on one rather than another of two neurones equally near together in space. This proximity and permeability are both provided for by the structure and constitution of the nervous system. It should be noted that the connection of neurones is not a one-to-one affair, but the