ABSTRACT
The essential functions of the nervous system are two: first, to mediate the sensibility of the organism to those changes in its surroundings which are significant to it; and, second, to initiate the responses of the contractile parts of the organism to those changes. The organism must, however, be also sensitive to the details of its own movements, if it is to respond adequately; and this is made possible by the proprioceptors, special organs of sensibility lying in and delicately affected by the conditions of muscle, joint, and tendon. The organism tends always to seek stimuli which are accompanied by pleasure, and to avoid those which bring pain. This is indeed one of the basic laws of the behaviour of living creatures. The organism is not passive clay in the hands of the environment; it is because the organism is dynamic that the environment can impose these conditions upon it.
