§ 3. Surplus Excitation.—It is clear that the agreeable or disagreeable feeling arising in connexion with the occurrence of a sensation may not be wholly due to the quality or intensity of the sensation itself. "If one is listening to a series of sounds, or looking intently at some object, the feeling of 'distraction' caused by being spoken to in a whisper, or lightly touche,"is comparable with sharp physical pain.* The whisper or the light touch may be in no way disagreeable in themselves; they may be virtually neutral; but they set up a general nervous and bodily disturbance, correlated with a general mental disturbance of an intensely unpleasant character. A similar shock is experienced when, in the process of going to sleep, we are startled by some sudden sound, which need not be especially loud. There is in such cases a diffused excitement of the nervous system, produced by the sensation, and superadded to that special excitement which is immediately correlated with the existence of the sensation. Following Professor Ladd, we may call this diffused effect the "surplus" excitation. Its occurrence is by no means confined to such exceptional experiences as that of being startled; on the contrary, all sensations which have a distinctly appreciable feeling-tone, appear to have a more or less diffusive character. In this respect, the difference between the organic sensation produced by a wound, and the special sensation produced by a bright light, is only one of degree.+ To some extent this statement may be directly verified by introspection: wherever feeling-tone is sufficiently intense, we can detect a diffused bodily and mental excitement, and concomitant change in our organic sensations. An intensely bitter taste may give rise to a cold shiver; the piercing scream of a railway whistle disturbs thought and perception, and is felt over the whole organism. A delicious taste may not only tickle the palate, but "set the whole man agog"; the strong pleasure or displeasure sometimes produced by stroking, tickling, or rubbing, is not immediately due to the quality and intensity of the tactile sensations themselves, but to the surplus excitement they produce. "We mentioned previously that sensations in themselves agreeable may in their general effect be unpleasing, and we found that the collateral unpleasantness can only in part be accounted for by the concomitance of definitely assignable and describable experiences. But surplus excitation, with consequent modification of common sensibility, adequately explains these subtle and evasive affections of consciousness. In the same way we are able to account for the qualitative diversity of the feeling-tone of different sensations which agree in being pleasant or unpleasant. The pleasure of a sweet taste differs in kind from that of a bright colour or of a musical note; and the difference cannot be wholly identified with the qualitative diversity of the sensations of sight, taste, and hearing themselves. Besides the variety of primary sensations, there is also a distinction between the kinds of pleasure which they afford. The several experiences contain elements which fulfil no other cognitive function than that of enabling reflective analysis to discriminate diverse modalities of feeling-tone. The existence of these diverse modalities has been strongly emphasized by Professor Ladd. "The way we feel is not by any means precisely the same for all equally pleasurable or equally piainful, tastes and smells. Some agreeable sweet odours are described as ' heavy,' and others as having an 'enlivening' or 'spicy' quality."* Compare, for instance, the heliotrope and the Japanese lily. The strong organic effect which may be produced by a powerful odour is shown by its sometimes causing highly susceptible persons to faint. "Pleasant coolness is 'refreshing': pleasant warmth is 'cherishing.'... Musicians have always attached different distinct kinds of feeling to different musical instruments," and "to different keys and chords .. . The 'grave' feeling belonging to the bass register is different otherwise than in mere quantity of pleasure-pain from the 'stirring' of the tenor,"+ These various experiences tend to induce certain moods having affinity with distinctive emotions. The same is true in a less degree of colours. ''Bright light and mellow light produce differences in the character of the equally pleasurable feeling which may result."+ Goethe contrasts the "cheerfulness" of a view as seen through yellow glass with its "mournfulness" as seen through blue glass. These differences in feeling-tone cannot be reduced to the mere difference between pleasantness and unpleasantness; and they cannot be identified with the qualitative differences between the sensible qualities which occupy attention, and which are said to be pleasant or unpleasant. We must refer them to a more or less diffused excitement of the nervous system with its organic consequences, and the resulting modifications of common sensibility.

* Ladd's Descriptive Psychology, p. 199.

+Hence there is no sharply marked line of demarcation between pain-sensation and the disagreeableness of special sensation. When unpleasant organic accompaniments become prominent, pain-sensation arises.

We have asserted that "all sensations which have a distinctly appreciable feeling-tone, appear to have a more or less diffusive character. "|| But we have not so far adduced evidence sufficient to justify this position in its full extent.

* Op. cit, p. 184. + Op. cit.,p. 185.

+ Ibid. § 3, p. 222.

Fortunately the deficiency is supplied by experiments, which, show that pleasant and unpleasant sensations in general produce organic effects differing in a characteristic way according as they are agreeable or disagreeable. By suitable apparatus it is possible to measure variations in the volume of the limbs, and in the respiratory movements, while the subject is undergoing pleasant or unpleasant experiences. The variations are recorded by a curve traced upon a revolving cylinder. The curve for the volume of the limb indicates, besides larger and longer variations, also smaller and shorter variations due to the beat of the pulse. The general results deduced from a careful analysis of these experiments are as follows.