Now the component currents are of different sizes and positions and variable degrees of warmth. That is another way of saying that whether or not a current is to become the center of the stream, or to approach it, or whether it is to be hot, cold, or tepid, depends upon the degree of activity of the various parts of the vegetative apparatus. A convenient name for this is _tonus_. Tonus can be experimentally watched and measured. Thus hunger, the most primitive of the wish-feelings, has been found to be simultaneous with certain characteristic contractions of the stomach. Stop those contractions, and you stop the hunger. The contractions begin slowly and weakly, and no awareness of them occurs in the mind. As they grow stronger, consciousness becomes a sensation rather like an itch somewhere in the upper abdomen, and accompanied sometimes by a sense of general weakness. The vegetative activity going on as a current almost on the outside of the stream of feeling has swelled and warmed, and so forced itself, in a manner of speaking, into the center of the stream. Or if you will, the rest of the stream has to arrange itself around it as the center. A similar mechanism for the tonus of the other members of the vegetative system, and how they determine consciousness and behaviour is understandable. It has been shown that when the bladder tone and the intestinal tone are of a definitely measurable size, one has the desire to empty them. The same applies to the sex glands. The pressure within a viscus is dependent upon the ratio between the amount of contraction of the involuntary muscle in its walls, the external pressure, and the quantity of its distending contents, the internal pressure. The resultant quotient, the internal pressure divided by the external pressure, measures the intravisceral pressure. The primitive wish-feelings are the direct expressions of the various intravisceral pressures, or tones. The primitive soul is an awareness of the fused primitive wish-feelings of themselves as a whole, and of the struggle between them for recognition, isolation, and, as we say, satisfaction. This satisfaction consists in a degradation of the highest intravisceral pressure to a point at which some other intravisceral pressure becomes higher and therefore predominant. PHYSICS OF THE WISH