The first difficulty consists in our not having a complete enumeration, on which all authors are agreed, of the internal sensations, as we have in the case of the special sensations. Beaunis gives a very detailed classification in eight groups; Kröner adopts a somewhat different one; both include pleasure, pain, and the emotions. Let us eliminate this last group (the affective manifestations) and confine ourselves to the vital sensations properly so called, connected with purely physiological needs, with the organs and functions indispensable to life: the different sensations of the alimentary canal (hunger, thirst, _malaise_, nausea, etc.); those of the respiratory apparatus (the need of fresh air, dyspnœa, asphyxia), of the circulatory apparatus, of the excretions and secretions; of the sexual organs in the normal state or in transitory phases (puberty, menstruation, pregnancy, menopause); the need of muscular movement, of rest, of sleep; the sensation of fatigue;—we have nearly all, if not all, the elements of cœnæsthesia, _i.e._, the consciousness of the body as living and acting. Have these multiplied sensations a common cause? Are they different modes of one and the same process? Do they imply, at their origin, the same stimulus, the same kind of excitement, as all the varieties of visual sensations suppose luminous vibrations, and the varieties of auditive sensations, sonorous vibrations? Kröner maintains that, for all internal sensations, the initial excitation is of a _chemical_ nature. “Every organic sensation is based on a chemical process, and arises according to the laws of diffusion and osmosis.”[83] The author justifies his assertion by the enumeration of a large number of facts, for which I refer the reader to his book. Chemical action, according to him, either takes place under the gaseous form (a person passes from the open air into a room full of deleterious miasma) or under the liquid (alcohol, toxic substances in solution in the fluids of the organism and introduced into the circulatory current). ----- Footnote 83: Kröner, _Das körperliche Gefühl_ (Breslau, 1887), pp. 102-112. -----