Pleasant sensations, such as that of a sweet taste or of a good cigar smoked by a person who enjoys it, produce increase in the volume of the limbs due to dilatation of the bloodvessels at the surface of the body. They also produce an increase in the height of the pulsebeat, which may be in part due to increased contraction of the heart. The respiration is deepened, and probably the muscles under the control of the will are in general more strongly contracted.

The case of unpleasant sensations is more complicated. On the first introduction of the unpleasant stimulus, the volume of the limb is distinctly diminished, owing to constriction of the bloodvessels at the surface of the body. The constriction at the surface of the body is probably accompanied by a dilatation of the bloodvessels of the internal organs. The amplitude of the pulsebeats is diminished. At the same time, there is a deepening of respiration; and when the stimulus is strong, there is a conspicuous contraction of the voluntary muscles in general. Later phases of the process present different phenomena.

After its initial diminution, the volume of the limb begins to increase, and continues increasing for some time. This increase is not supposed to be in the first instance due to dilatation of the bloodvessels, but to accumulation of venous blood arising from decreased activity of the heart. But dilatation of the bloodvessels following by way of reaction on their previous constriction is supposed to contribute to it at a later stage. The increased innervation of the voluntary muscles is also followed by a corresponding relaxation.

These experiments justify the assumption that all sensations having a distinctly appreciable feeling-tone produce a diffused organic effect, which differs in a characteristic way, according as they are pleasant or unpleasant.

There thus appear to be three factors which may contribute to determine feeling-tone: (1) The sensation itself; (2) The diffused excitement of the nervous system which it may produce; (3) The effect of this diffused excitation on the organism by the consequent alterations of common sensibility which arise from the altered state of the internal organs. All three factors probably contribute to the result in varying degrees according to circumstances. It seems arbitrary to select one of them as alone important to the exclusion of the others: but some writers show a tendency to do so. For instance, Professor Ladd lays stress exclusively on the diffused excitement of the nervous system directly occasioned by the occurrence of the sensation. He seems to regard the sensation itself as devoid of feeling-tone, and he seems to attach little or no importance to the organic sensations which it indirectly produces. But introspection shows that a sensation may be in itself agreeable or disagreeable apart from its effects. Thus, sweetness may in its own intrinsic nature be agreeable, though on the whole it awakens disgust. Another view, which seems favoured by Professor James, is that feeling-tone belongs exclusively, or almost exclusively, to organic sensation. He is not very clear on the point, but it seems to form part of his celebrated theory of emotion that, apart from organic sensation, our mental states would consist almost wholly in cold intellectual perception without feeling-tone. At any rate, it is important to discuss the point, if for no other reason, because of its bearing on a theory which we shall have to examine later,—the theory which reduces emotion, and the pleasantness and unpleasantness of emotion, to organic sensations and their feeling-tone.

On the psychological side, the distinction between pleasantness and unpleasantness is simple and ultimate. If it is due to a difference in organic conditions, we should expect this difference to be equally simple. Now we do not find that the contrast between the organic processes is correspondingly simple. On the contrary, even those organic concomitants of feeling-tone which can be detected by experiment are very complicated. Thus, in the case of unpleasant experiences, initial constriction of the bloodvessels at the surface of the body is accompanied by dilatation of the bloodvessels of the internal organs. The constriction of the surface is in a subsequent phase of the process probably followed by dilatation at the surface. The initial diminution of the volume of the limb is followed by increase due to accumulated venous blood. So increased contraction of the voluntary muscles is followed by relaxation. Hence we cannot single out any general form of organic stimulation as the universal and uniform condition of unpleasant feeling-tone. There is therefore no theoretical advantage in ascribing feeling-tone exclusively to organic sensations.

The same problem confronts us in regard to them as in the case of the special senses. They constitute a heterogeneous group of experiences, some of which are pleasant and some unpleasant. Each of them has, besides its feeling-tone, its own specific quality as a sensation, and this quality may be almost neutral in tone, or it may have both agreeable and disagreeable phases according to its intensity, or according to the general mental condition at the moment. Neither in their internal nature, as analysed by introspection, nor in their mode of origin, do organic sensations present any peculiar characteristics which would justify us in making so vast and important a distinction between them and the sensations of the special senses, as is involved in affirming that they alone can be pleasant or painful, while the sensations of the special senses are neutral. It is true that organic sensations have a peculiarly diffusive character, but even in this respect the distinction between them and the special sensations is only one of degree. A positive argument against the hypothesis may be derived from the fact that the emergence of a simple sensation in a given phase of intensity, and the emergence of its feeling-tone, are not separated by any appreciable interval of time. But the production of organic changes by the original stimulation of the nervous system, and the production of organic sensations in consequence of these changes, is a process which must occupy an appreciable time. In fact, the later addition of new elements to the original experience can frequently be detected by introspection. A very bitter taste may, as Lehmann remarks, appear at first merely as a disagreeable bitterness, which is followed only after an appreciable interval of time by a cold shiver due to constriction of the bloodvessels.

We conclude therefore that it is unjustifiable and arbitrary to ascribe feeling-tone exclusively either to the primary sensation, or to the surplus nervous excitement which it produces, or to the resulting organic sensations. All three factors contribute, and they may contribute in different proportions according to circumstances.