HUNGER AND APPETITE 477 



trol 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 auto- 

 matically 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 gastric tonus and augments the gastric hunger contrac- 

 tions. 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. Section of both the splanchnic and vagus nerves throws 

 the stomach into a permanent hypotonus, except in prolonged starva- 

 tion, when hunger contractions develop that are usually of great ampli- 

 tude and with particularly long intervals between the contractions. 

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

 although completely isolated from the central nervous system, the 

 stomach still exhibits typical hunger 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 stimuli that may set up impulses traveling by the extrin- 

 sic nerves to the stomach are conveyed by the nerves of sense or are of 

 psychic origin. Stimulation of the gustatory end organs in the mouth, 

 as by chewing palatable food, always causes an inhibition of the tonus 

 and a diminution or disappearance of the hunger contractions. Even the 

 chewing of indifferent substances, such as paraffin, suffices to produce 

 distinct inhibition, unless in a case in which the contraction has passed 

 into a tetanus. It is of interest that swallowing movements, in the ab- 

 sence of any food substance in the mouth, are sufficient to produce a 

 transitory inhibition of the gastric tonus a receptive relaxation of the 



