one, when established, cannot be disjoined, any more than that of the other. Consequently, stimulation of such a group of ideas calls it into action, and then arises its special feeling, depending in degree upon the amount of the stimulation and the nerve-force extricated in the process. And these very complex emotions may be reduced by analysis to much simpler feelings—to feelings of self-advantage or self-detriment, the pleasure or pain which is at the bottom of all feeling, of all stimulation of the nervous system strong enough to cause feeling to come into consciousness. Looking upon the whole conscious brain as self, its feeling varies from self-good to self-ill; its various and special portions, groups of nerve-cells and nerve-centres, being stimulated into special feelings which are yet all of them resolvable into the simple elements. If we look at the phenomena of insanity we shall see this illustrated by the fact that the feelings and delusions of the insane always have reference to self.
I have traced the higher emotions up from the mere bodily feelings, nay, even from the sensations of the special senses, and have affirmed that they all vary according to the amount of stimulation which each centre receives, while their quality depends on the special properties of the centre or centres. The phenomena of two of the senses, at any rate, confirm this view. One person hears a sound which another cannot. This is because the centre of hearing in the deaf person is not sufficiently stimulated by a sound, the vibrations of which are too slow for him, though not too slow for the other to perceive. Similarly, some people cannot recognize redness as a color. On analyzing the color red, we find it to be the color at one end of the spectrum, an inch of which gives the smallest number of waves of light, and to this amount of stimulation some eyes are insensible, just as the eyes of all men are insensible to the rays beyond red, which we discover by the galvanometer, though they do not excite our optic centres as light. As no two persons feel alike, so no two see or hear alike. The centres of sight and hearing of one man are stimulated by vibrations which fail to excite those of another. There may be colors and there may be harmonies all around us in the universe, of which we know nothing, but of which the more sensitive organs of what are called the lower animals may be keenly conscious. It may be that these animals are only by us called dumb because we ourselves are deaf.
The stimuli, then, which excite the nerve-centres of man, produce various feelings and emotions according to the quality and properties of the centre excited. But, as I have said, the feeling will vary according not only to the quality of the centre, but also according to the condition it may happen to be in at the time, or that to which it may be brought by the stimulation it experiences. To elucidate this, we must consider what we know of the physiology of nerve-structures and their functions.
