11. Of the chief directions of feeling mentioned above, especially that of pleasarable and unpleasurable feelings can be shown to stand in regular relation to the pulse. When the feeling is pleasurable, the pulse is retarded and intensified, when unpleasurable, the pulse is accelerated and weakened. For the other directions, the accompanying changes can only be inferred with some degree of probability, from the effects of the corresponding emotions (§13, 5). Thus, exciting feelings seem to betray their presence only through stronger pulse beats, and subduing through weaker, without a change of rate in either case. For feelings of strain, we have retarded and weakened pulse, for those of relaxation, accelerated and intensified pulse. Single feelings belong for the most part to several of these directions at the same time; as a result, the action of the pulse is in many cases so complex that the most that can be concluded is the predominance of one or the other direction. The conclusion is, however, uncertain so long as it is not confirmed by direct observation of the feeling.

11a. The relations that seem probable from experiments on the symptoms of feelings and emotions as found in pulse-activity, may be presented in the following scheme. Exciting and subduing feelings, then, show themselves by simple changes in the pulse, the others by double changes. But [p. 88] this scheme, which is derived for the most part from the effect of complex emotions, needs confirmation from experiments in which attention is paid to the isolation of these various affective directions. Changes in respiration, muscle-tension, etc., also need further investigation. It is obvious from the equivocal character of each symptom, that when a particular feeling is given in psychical experience, we can infer particular resulting innervations from the symptoms which appear, but that we can never infer the presence of particular feelings from the physiological symptoms. It follows that the expression-method can not be as highly valued from a psychological point of view as the impression-method.

>From the very nature of the case, the impression-method is the only one that can be used in arousing and varying psychical processes at will. The expression-method gives results that explain only the physiological phenomena which accompany feelings, not the psychological nature of the feelings themselves.

The variations observed in the pulse must be regarded as the results of a changed innervation of the heart, coming from the cardiac centre in the brain. Physiology shows that the heart is connected with the central organs by two kinds of nerves: excitatory nerves, which run through the sympathetic system and originate indirectly in the medulla, and inhibitory nerves, which belong to the tenth cranial nerve (vagus) and also have their source in the medulla. The normal regularity of the pulse depends on a certain equilibrium between excitatory and inhibitory influences.

Such influences come not only from the brain, but from the centres in the ganglia of the heart itself. Thus, every increase and every decrease of the heart's energy may be interpreted in two different ways. The first may be due to an increase of excitatory, or to a decrease of inhibitory innervation, and the second may be due to a decrease in excitatory or to an increase in inhibitory innervation, or in both cases the two influences may be united. We have no universally applicable means of investigating these possibilities, still, the circumstance that the stimulation of the inhibitory nerves has a quicker effect than the stimulation of the excitatory, gives us good ground in many cases for conjecturing the presence of the one or the other. Now, the changes in the pulse always follow very quickly the sensations that cause them. It is, therefore, probable that in the case of feelings and emotions, we have [p. 89] chiefly changes in inhibitory innervation, originating in the brain and conducted along the vagus. It may well be assumed that the affective tone of a sensation on its physiological side, corresponds to a spreading of the stimulation from the sensory centre to other central regions which are connected with the sources of the inhibitory nerves of the heart. Which central regions are thus affected, we do not know. But the circumstance that the physiological substrata for all the elements of our psychological experience, are in all probability to be found in the cerebral cortex, leads very naturally to the assumption that the same is true for the centre of these inhibitory innervations. Furthermore, the essential differences between the attributes of feelings and those of sensations, make it probable that this centre is not identical with the sensory centres. If a special cortical region is assumed as the medium for these effects, there is no reason for supposing a special one for each sensory centre, but the complete uniformity in the physiological symptoms goes more to show that there is only one such region, which must then at the same time serve as a kind of central organ for the connection of the various sensory centres. (For the further significance of such a central region, and its probable anatomical position, compare §15, 2a.)