The advocates of the theory of organic evolution early pointed out the similarity between the bodily disturbances in pain and in the major emotions. The alterations of function of internal organs they could not know about. The general statement, however, that pain evokes the same changes that are evoked by emotion, is true also of these deep-lying structures. Wertheimer[18] proved many years since that stimulation of a sensory nerve in an anesthetized animal--such stimulation as in a conscious animal would induce pain--quickly abolished the contractions of the stomach. And Netschaiev, working in Pawlow’s[19] laboratory, showed that excitation of the sensory fibres in the sciatic nerve for two or three minutes resulted in an inhibition of the secretion of gastric juice that lasted for several hours. Similar effects from painful experience have been not uncommonly noted in human beings. Mantegazza,[20] in his account of the physiology of pain, has cited a number of such examples, and from them he has concluded that pain interferes with digestion by lessening appetite and by producing various forms of dyspepsia, with arrest of gastric digestion, and with vomiting and diarrhea. The expression, “sickening pain” is testimony to the power of strong sensory stimulation to upset the digestive processes profoundly. Vomiting is as likely to follow violent pain as it is to follow strong emotion. A “sick headache” may be, indeed, a sequence of events in which the pain from the headache is primary, and the nausea and other evidences of digestive disorder are secondary. As the foregoing account has shown, emotional conditions or “feelings” may be accompanied by quite opposite effects in the alimentary canal, some highly favorable to good digestion, some highly disturbing. It is an interesting fact that the feelings having these antagonistic actions are typically expressed through nerve supplies which are correspondingly opposed in their influence on the digestive organs. The antagonism between these nerve supplies is of fundamental importance in understanding not only the operation of conditions favorable or unfavorable to digestion but also in obtaining insight into the conflicts of emotional states. Since a consideration of the arrangement and mode of action of these nerves will establish a firm basis for later analysis and conclusions, they will next be considered. REFERENCES [Footnote 1: Pawlow: The Work of the Digestive Glands, London, 1902.] [Footnote 2: Bidder and Schmidt: Die Verdauungssäfte und der Stoffwechsel, Leipzig, 1852, p. 35.] [Footnote 3: Richet: Journal de l’Anatomie et de la Physiologie, 1878, xiv, p. 170.] [Footnote 4: See Hornborg: Skandinavisches Archiv für Physiologie, 1904, xv, p. 248. Cade and Latarjet: Journal de Physiologie et Pathologie Générale, 1905, vii, p. 221. Bogen: Archiv für die gesammte Physiologie, 1907, cxvii, p. 156. Lavenson: Archives of Internal Medicine, 1909, iv, p. 271.]