There is another possible hypothesis, quite different from the others, which I should be willing to accept, but which cannot be presented as more than a theory. It would consist in attributing the genesis of pain to _chemical modifications_ in the tissues and nerves, especially the production of local or general toxins in the organism. Pain would thus be one of the forms of auto-intoxication. Oppenheimer alone seems to me to have worked in this direction.[28] In his opinion, as regards the origin of pain, “the real cause, in any sensorial or other organ, resides in a change in the tissues, especially a chemical change, by which either the products of destruction rise above the normal average, or else modifications result from the presence of a foreign body in the organism.” The connection between the peripheral tissues and the centres would be by the vaso-motor nerves (constrictor or dilator). The tissues would be the terminal organs of pain, the vaso-motors the paths of conduction. In organs which only undergo slight changes when active (tendons, ligaments, bones, etc.) conscious sensibility is almost absent. “Pain is not, as many believe, the highest degree of sensation produced in the organs of special sense; it is the most intense sensation produced in the vaso-motor nerves under the influence of violent stimulation.” ----- Footnote 28: _Schmerz. und Temperaturempfindung_, Berlin, 1893. ----- This hypothesis will perhaps be justified by the future. I shall return to it when studying the emotions. We shall then see that these are accompanied by deep and well-established chemical modifications in the organism. Physical pain is a large subject, which, as may be seen, has not been neglected of late, and concerning which there is still much to say. It is not possible, however, to deal further with it here, since it only occupies a limited area in the psychology of the emotions. CHAPTER II. MORAL PAIN. _Identity of all the forms of pain—Evolution of moral pain: (1) the pure result of memory; (2) connected with representations; positive form, negative form; (3) connected with concepts—Its external study; physical signs—Therapeutics—Conclusions—A typical case of hypochondriasis._