ORGANIC SENSATIONS. "Sensations ade quately stimulated by changes in the condition of the bodily organs—muscles, joints, etc. In every case, the adequate stimulus consists of a change in the condition of the particular organ, and the organ itself is the peripheral seat of origin of the nervous excitation which is thus set up." (Kiilpe.) The only difference, then, be tween the 'sensations of special sense' and the organic sensations is that the organs of the for mer are stimulated from without, by some move ment-process in the external world, while the latter are aroused by a bodily process within the organ itself. The distinction is convenient for purposes of classification, but has no psycholog ical importance, since the sensations of the 'five senses' also presuppose a change in their organ; the 'stimulus' makes its impression on the brain by way of a bodily process in eye, ear, etc. In deed, that there is no difference of kind between the two classes of sensations is shown by the at titude of popular psychology, which sometimes speaks of the 'five senses,' as if there were no more, but sometimes also adds a sixth sense, the 'muscle sense' (q.v.), to the five external senses.
The organic sensations, so far as they are known, fall into six principal groups. (1) We have, first, the group of 'kinaesthetic' sensations, the sensations which are excited by movements and similar stimuli (weight, resistance, position, etc.), and which furnish us with our bodily (non visual) knowledge of the movement and position of the members. The specific quality of muscular sensation is a dull, dead pressure; that of tendin ous sensation is strain; and that of articular sensation, the sensation set up by the rubbing or jamming of the joint surfaces, is a sharp pres sure, which appears to be identical with the pressure obtained from the pressure-spots of the culls. ( See CUTANEOUS SENSATIONS.) These qualities have been identified, in the complex experiences within which they normally occur, partly by the laboratory method of elimination, and partly by the investigation of pathological cases. We can, e.g. by keeping tine member un moved and etherizing the skin. stimulate the muscle alone; or again, by etherizing the skin and nmscle, stimulate the joint alone; or again, by passing a strong induction current through the joint, practically rule out the articular sen sations. Since our sensitivity for lifted weights remains but little impaired when the sensations from skin and muscle are thins ruled out, Ave refer this function to the tendinous strain sen sation, which remains clear in consciousness. Since a similar elimination does not affect our judgments of position and movement, while elimination of the joint sensations renders them extremely uncertain, we refer these functions, in the same way, to the articular surfaces. )n the pathological side, we find normal judgment of the position of the limbs compatible pith anaesthesia of the external skin and muscles: if the whole limb is insensitive there is no knowledge of its movement or place. More
over, patients of the first class give the most accurate judgments of position and movement if the articular surfaces are closely pressed together.
(2) Of great importanee in the economy of the organism are the alimentary organic sensa tions. These are three in number: the sensation of hunger, from the stomach; that of thirst, from the pharynx: and that of nausea. from the (esophagus. The adequate stimulus to hunger appears to consist in the drying and folding of the gastric mucous membrane, the lining of the `wall' of the stomach, though hunger may be relieved by the injection of food into the large intestine. Thirst is set up by the drying of the pharyngeal mucous membrane, and may be re lieved (though not permanently) by painting the back of the throat with a weak solution, e.g.
of citric acid. The stimulus to nausea is. per haps, the antiperistaltic movement of the 'esoph agus. which. in extreme form, passes over into the vomiting reflex. The experience of nausea usually includes sensations of taste, smell. and dizziness (see 6 below), so that the isolation of its specific quality is extremely difficult.
(3) There seems to be no doubt that circula tory sensations, stimulated by changed conditions of blood movement and blood supply, appear in certain organic complexes. though we cannot identify them with any degree of accuracy, or do more than guess at the conditions of their origin.
Itching, tingling, formication. pins and needles, creeping. tickling, feverishness. etc., are the complexes in question. The sensation of cutane ous warmth that follows upon the pain of a smart blow upon the palm of the hand is pos sibly referable to circulatory sensations, though it may also be a true temperature sensation.
(4 ? Much the same thing, must be said of the respieutory sensation?. There seems to be a specific breathing quality in such experiences as panting. stuffiness, a bracing air, 'second wind,' breathlessness. etc.; and the lungs contain sen sory nerve-endings. But of the number and nature of the respiratory qualities we are still ignorant.
(5) No systematic study has so far been made of sf xnal sensation. The sensation of lust is presumably the same in both sexes. We know. however. nothing in detail of its terminal organs. and little of its distribution over the organs of sex.
(6) The sensation of dizziness nr giddiness is mediated by the semicircular canals of the in ternal ear. which are supplied by the vestibular branch of the auditory nerve. (See EAR.) The semicircular canals and vestibule constitute an organ which assists us, reflexly. to maintain our equilibrium and to orientate ourselves in space.
Under certain conditions (for which see STATIC