great pain and intense muscular action would be experienced. Now the emotions are as purely motor excitants as is pain. The dynamic result is the same the principal difference being the greater suddenness and the absolute specificity of the pain stimuli as compared with the more complex and less peremptory stimuli of the emotions. A further evidence that pain is a product of the release of brain-cell energy is the probability that if one could pierce the skin at many points on a limb in such a manner that antagonistic points only were equally and simultaneously stimulated, then an equilibrium in the governing brain- cells would be established and neither pain nor motion would follow. An absolute test of this assumption cannot be made but it is supported by the obtainable evidence. We will now turn to a new viewpoint, a practical as well as a fascinating one, which can best be illustrated by two case histories: A man, seventy-eight years old, whose chief complaint was obstinate constipation, was admitted to the medical ward of the Lakeside Hospital several years ago. The abdomen was but slightly distended; there was no fever, no increased leukocytosis, no muscular rigidity, and but slight general tenderness. He claimed to have lost in weight and strength during the several months previous to his admission. A tentative diagnosis of malignant tumor of the large intestine was made, but free movements weresecured rather easily, and we abandoned the idea of an exploratory operation. The patient gradually failed and died without a definite diagnosis having been made by either the medical or the surgical service. At autopsy there was found a wide-spread peritonitis arising from a perforated appendix. A child, several years old, was taken ill with some indefinite disease. A number of the ablest medical and surgical consultants of a leading medical center thoroughly and repeatedly investigated the case. Although they could make no definite diagnosis they all agreed that the trouble surely could not be appendicitis because there was neither muscular rigidity nor tenderness. The autopsy showed a gangrenous appendix and general peritonitis. How can these apparently anomalous cases be explained? These two cases are illustrations of the same principle that underlies the freedom from pain which results from the use of narcotics and anesthetics, the same principle that explains the fact that cholecystitis may occur in the aged without any other local symptoms than the presence of a mass and perhaps very slight tenderness; and that accounts in general for the lack of well-expressed disease phenomena in senility and in infancy. The reason why the aged, the very young, and the subjects of general paresis show but few symptoms of disease is that in senility the brain is deteriorated, while in infancy the brain is so undeveloped that the mechanism of association is inactive, hence pain and tenderness, which are among the oldest of the associations, are wanting.