§ 4. Organic Sensations.—The sensations we have so far considered derive their main importance from the function they fulfil in the perception of external objects. Their specific qualities correspond not only to the specific modes in which the organism is affected, but also to the specific nature of the agencies which act upon it. It is true that * On this point Wundt's own statements are somewhat vague motor sensations do not arise from external impressions: they originate within the organism itself. But they none the less play a most important part in the perception of external things. It is through them that we appreciate weight, resistance, and spacerelations. But there is another class of sensations which mainly mark states of the organism itself, and not the nature of external objects. These are called organic sensations. Extreme heat and extreme cold no longer produce sensations distinctive of heat and cold at all; they both produce a peculiar painful experience, which is the same whether the external agency is heat or cold. In like manner, the sensations resulting from a bruise, a blow, or a cut, may be similar, though they are produced by very various external agencies. It is characteristic of such sensations that they persist often for a long time after the external agency has ceased to operate. The bodily change which it has produced continues to act as a persistent stimulus. A wound persists after the knife which has inflicted it is withdrawn, and along with the wound the sensation occasioned by it persists also. Organic experiences may arise either through the operation of an external agency, or merely through the changing states of the internal organs. Hunger and thirst and the like are familiar examples of sensations originating from within the organism itself. Motor experiences, as we have seen, generally mark the qualities and relations of external things; but the sensations of fatigue or of cramp are truly organic, because they mark the state of the muscular apparatus itself, and do not contribute to our knowledge of the external world. In every moment of our lives organic sensations constitute a most important element in our experience. The general tone of our bodily feeling depends on them. On them depends the difference between feeling well and feeling ill, and the like. But this or that organic sensation does not attract attention and emerge clearly into consciousness, unless it attains a special pitch of intensity. In general, organic experiences from manifold sources are merged in a massive whole constituting what is called the common sensibility or coenaesthesis. When, from the general mass of common sensibility, a single organic sensation detaches itself and becomes salient in consciousness, it is usually intrusive and engrossing. Such sensations are specially characterised by their diffusiveness. They do not, like sensations of sight or pressure, depend merely on the localised affection of a circumscribed portion of the organism; they also involve a more or less widespread organic disturbance. For instance, the pain-sensation produced by a cut or a blow is a complex experience partly depending on the disturbance of respiration, circulation, and the whole motor apparatus of the body. The more intense the sensation, the more conspicuous and widespread is this general organic disturbance.

This brings us to another aspect of organic sensation. It may arise, and usually does arise in part, from a disturbance of the nervous system, which excites changes throughout the organism, these changes in their turn giving rise to sensations. In all the more intense emotions, there is an accompaniment of organic sensation originating in this manner. This is so important an element in the total state that it has been held to constitute the essential part of the emotional experience.

* Book i., chap, ii., § 9, ad fin. The Various Modes of Specific Reproduction

We have seen* that the possibility of central initiation makes organic sensations reproducible as no other sensations are under normal conditions. Whatever reinstates a similar nervous disturbance, will indirectly produce similar organic sensations. Tickling, for instance, is a very diffusive experience; and the mere anticipation will produce the corresponding organic sensations, because it produces the general disturbance of nervous equilibrium on which they depend. The uncomfortable feelings which arise in paying a visit to a dentist, even before he begins operations, have the same source.

We shall have something to say about pain-sensations in general in a subsequent chapter. "We need here only refer to two organic experiences of special importance, hunger and thirst. Thirst is usually produced "by the diminution of the water present in the body either through restriction of the intake, or through excess of the output in the secretions, such as that of sweat, or through both together.....Thirst thus brought about may be temporarily assuaged by simple moistening of the soft palate. From this we may infer that the sensation of thirst is brought about by afferent sensory impulses started in the mucous membrane of the soft palate by a deficiency of water in that membrane."* Hunger is usually "produced by the products of digestion ceasing to be thrown into the blood." The sensation seems "to be in some way specially connected with the condition of the gastric walls, much in the same way that thirst is specially connected with the palate; the products of digestion have a much greater power in appeasing hunger when they act locally and directly on the gastric membrane than when they are simply brought to bear on the body at large, and a small quantity of food will immediately satisfy hunger when introduced into the stomach, though it will have no effect when introduced otherwise."+ * Foster, op. cit., p. 1423.                    + Op. cit., p. 1424.