296 THE POPULAR SCIENCE MONTHLY 



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, 14 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, 15 and yet because 

 animals eat after one or another set of nerves is eliminated, the conclu- 

 sion has been drawn by various writers that the nerves in question are 

 thereby proved to be not concerned in the sensation of hunger. Evi- 

 dently, 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 funda- 

 mental 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 evi- 

 dence 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; 16 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 insensi- 

 tivity 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, "Traite de physiologie," Paris, 1868, L, p. 23. 

 "Ludwig, "Lehrbuch der Physiologie des Menschen," Leipzig and Heidel- 

 berg, 1858, II., p. 584. 



1(1 Maxwell, Journal of Biological Chemistry, 1906-7, II., p. 194. 



