HUNGER AND APPETITE 511 



of time unanimously attest to the fact that, after the first few days, the 

 sensations of hunger become less pronounced and finally almost dis- 

 appear, they must have experienced the most distressing period during 

 their four days of starvation. Although the hunger sensation was 

 strong enough to cause some discomfort, it could by no means be called 

 marked pain or suffering, and was at no time of sufficient intensity to 

 interfere seriously with work. Mere starvation cannot therefore be 

 designated as acute suffering. It is of further interest to note that dur- 

 ing the starvation period a continuous flow of .secretion of acid gastric 

 juice was found to be occurring in the stomach, to the presence of which 

 acid or burning sensation experienced in the epigastrium on the last days 

 is probably to be attributed. 



Control of the Hunger Mechanism. The control of the hunger mecha- 

 nism, like that of any other mechanism in the animal body, may be ef- 

 fected through the nervous system or it may depend on the presence of 

 chemical substances or hormones in the blood. As a matter of fact, it 

 can readily be shown that both those methods of control are employed, 

 and we will now consider briefly some of the facts upon which this con- 

 clusion depends. 



Although many facts are now known with regard to the nervous control of the 

 hunger mechanism, it is difficult to piece these together in such a way as to formulate 

 a simple theory which fits in with all the observed facts. We know that the stomach 

 possesses in itself a local nervous mechanism by which, like the heart or intestine, it 

 can automatically perform many of the movements which are exhibited in the intact 

 animal. These local movements may, however, be considerably influenced by impulses 

 transmitted to the stomach along the vagus and splanchnic nerves. We have therefore 

 to seek for evidence indicating the relative importance of the local nervous mechanism 

 in the stomach itself and of the impulses transmitted to this organ by the extrinsic 

 nerves. We must then seek the position of the center which perceives the sensation 

 of hunger. 



It will be simplest to consider first the effect of section of the extrinsic nerves in 

 observations made on lower animals. Section of the splanchnic nerves increases gas- 

 trie tonus and augments the gastric hunger contractions. Section of both vagus nerves, 

 performed of course below the level of the heart, leaves the stomach in a more or less 

 hypotonic condition. The tonus is not entirely abolished; it varies somewhat from 

 day to day, and may become quite pronounced even though the vagi are cut. In this 

 hypotonic state the hunger contractions are diminished in rate and regularity. Sec- 

 tion of both the splanchnic and vagus nerves throws the stomach into a permanent 

 hypotonus, except in prolonged starvation, when hunger contractions develop that are 

 usually of great amplitude and with particularly long intervals between the contrac- 

 tions. The general conclusion to be drawn from these experiments is that, although 

 completely isolated from the central nervous system, the stomach still exhibits typical 

 hunp-er contractions, which must therefore be essentially dependent upon an automatic 

 mechanism in the stomach wall itself. Over this mechanism, extrinsic nerve impulses 

 have merely a regulatory control. 



Variations and Inhibitions of the Hunger Contractions. The afferent 



