the scalp. A cold compress by constricting the blood-vessels reduces the din of the multitudinous messages shouted into consciousness by the sense-organs of the scalp. If completely successful it subdues their chorus to its habitual murmur, too faint to secure attention. Long continued, and therefore damaging, contraction of the muscles which move the eye-ball, and particularly its elevator, sends through their protopathic nerves a stream of influence to the mid-brain, with which these nerves are connected, which causes frontal headache in just the same way as the influence which ascends the stomach nerve.
Would doctors be more logical if they said that the headache was in the hind-brain—the region which contains the agitated gray matter which gives pain-value to the impulses from the scalp—or if they said it was in the stomach? The irritation of nerve-endings in the stomach is the origin of the trouble, seeing that it sets up the pain-condition in the hind-brain.
Psychologists base their science upon conspicuous sensations—sensations of sufficient prominence to stand out in the field of consciousness. They can do no otherwise. But the terminology in which they have expressed the results of their analysis hampers physiology. In the process of conduction a physiologist can distinguish no stages intermediate between stimulation and muscular response. In reactions to which consciousness is adjunct, as judged by self-feeling, or, when outside oneself by attribution of self-feeling, the nerve-current may be termed a sensation, and sensations may or may not provoke attention. Nothing is gained by classifying the sequence of events into stimulation, passage of impulse, sensation, perception. Such terms are machinomorphic. The nervous mechanism is infinitely vibrating. "I always hear my clock stop" can have but one meaning. Every tick of the clock produces an answering vibration of the auditory nerve, however little attention be given to the message; and attention carries with it the idea of something which attends. Pain, as pictured in this essay, is the interpretation which the ego gives of hitherto unperceived sensations when they are increased in volume without definition. Pain is developed when impulses, without informing attributes, are raised in urgency to the level of attention.
The passage of a gall-stone from the gall-bladder to the intestine is the cause of intense pain, "referred," in the first instance, to the skin which overlies the liver. Yet the gall-bladder is insensitive. As surgeons have long been aware, the liver, stomach and other viscera may be cut, burned, scarified, without arousing pain. Laying stress on these two well-known facts, (1) the insensitiveness of the viscera and (2) their liability to become the source of referred pains, James Mackenzie has defined pain as "a disagreeable sensation due to stimulation of some portion of the cerebrospinal nervous system and referred to the peripheral distribution in the body wall of cerebrospinal sensory
