The adequate stimulus for the ticklish points of the ribs, the loins, the abdomen, and the neck is deep isolated pressure, probably the most adequate being pressure by a tooth-shaped body. The response to tickling in these regions is actively and obviously self-defensive. The horse discharges energy in the form of a kick; the dog wriggles and makes a counter-bite; the man makes efforts at defense and escape. There is strong evidence that the deep ticklish points of the body were developed through vast periods of fighting with teeth and claws (Fig. 9). Even puppies at play bite each other in their ticklish points and thus give a recapitulation of their ancestral battles and of the real battles to come (Fig. 10). The mere fact that animals fight effectively in the dark and always according to the habit of their species supports the belief that the fighting of animals is not an intellectual but a reflex process. There are no rules which govern the conduct of a fight between animals. The events follow each other with such kaleidoscopic rapidity that the process is but a series of automatic stimulations and physiologic reactions. Whatever their significance, therefore, it is certain that man did not come either accidentally or without purpose into possession of the deep ticklish regions of his chest and abdomen. Should any one doubt the vast power that adequate stimulation of these regions possesses in causing the discharge of energy, let him be bound hand and foot and vigorously tickled for an hour. What would happen? He would be as completely exhausted as though he had experienced a major surgical operation or had run a Marathon race. A close analogy to the reflex process in the fighting of animals is shown in the role played by the sexual receptors in conjugation. Adequate stimulation of either of these two distinct groups of receptors, the sexual and the noci, causes specific behavior-- the one toward embrace, the other toward repulsion. Again, one of the most peremptory causes of the discharge of energy is that due to an attempt to obstruct forcibly the mouth and the nose so that asphyxia is threatened. Under such conditions neither friend nor foe is trusted, and a desperate struggle for air ensues. It will be readily granted that the reactions to prevent suffocation were established for the purpose of self-preservation, but the discharge of nerve-muscular energy to this particular end is no more specific and no more shows adaptive qualities than do the preceding examples. Even the proposal to bind one down hand and foot excites resentment, a feeling originally suggested by the need for self-preservation. No patient views with equanimity the application of shackles as a preparation for anesthesia.