The unit response motives are imposed upon the behaviour of the animal by the integrative mechanisms, their innate laws of functioning, and the existing conditions of tonic nervous excitation natural to that particular organism. The drive motives are imposed upon the animal’s behaviour by the hormones and other spontaneous bodily stimuli causing changes in the natural or usual state of tonic nervous excitation. Human motives present, a much more complex picture than do animal motives, and are consequently much more difficult to analyze experimentally. There undoubtedly exist a great number of human acts which spontaneously seek self-enlargement, and which are not attributable by any stretch of the imagination to the influence of environment outside the organism itself. These actions are motivated by hunger drive from within.