shown. We have already seen that appetite as well as hunger may lead to the taking of food. Indeed, the animal with all gastrointestinal nerves cut may have the same incentive to eat that a well-fed man may have, who delights in the pleasurable taste and smell of food and knows nothing of hunger pangs. Even when the nerves of taste are cut, as in Longet's experiments, sensations of smell are still possible, as well as agreeable associations which can be roused by sight. More than fifty years ago Ludwig pointed out that, even if all the nerves were severed, psychic reasons could be given for the taking of food, and yet because animals eat after one or another set of nerves is eliminated, the conclusion has been drawn by various writers that the nerves in question are thereby proved to be not concerned in the sensation of hunger. Evidently, since hunger is not required for eating, the fact that an animal eats is no testimony whatever that the animal is hungry, and therefore, after nerves have been severed, is no proof that hunger is of central origin.
Weakness of the Assumptions Underlying the Theory that Hunger is a General Sensation.—The evidence thus far examined has been shown to afford only shaky support for the theory that hunger is a general sensation. The theory, furthermore, is weak in its fundamental assumptions. There is no clear indication, for example, that the blood undergoes, or has undergone, any marked change, chemical or physical, when the first stages of hunger appear. There is no evidence of any direct chemical stimulation of the gray matter of the cerebral cortex. Indeed, attempts to excite the gray matter artificially by chemical agents have been without results; and even electrical stimulation, which is effective, must, in order to produce movements, be so powerful that the movements have been attributed to excitation of underlying white matter rather than cells in the gray. This insensitivity of cortical cells to direct stimulation is not at all favorable to the notion that they are sentinels set to warn against too great diminution of bodily supplies.
Body Need may Exist without Hunger.—Still further evidence opposed to the theory that hunger results directly from the using up of organic stores is found in patients suffering from fever. Metabolism in fever patients is augmented, body substance is destroyed to such a degree that the weight of the patient may be greatly reduced, and yet the sensation of hunger under these conditions of increased need is wholly lacking.
Again, if a person is hungry and takes food, the sensation is sup-
- Longet, "Traité de physiologie," Paris, 1868, L, p. 23.
- Ludwig, "Lehrbuch der Physiologie des Menschen," Leipzig and Heidelberg, 1858, II., p. 584.
- Maxwell, Journal of Biological Chemistry, 1906-7, II., p. 194.