HUNGER AND APPETITE 473 



increases in intensity, until by the time the stomach has nearly emptied 

 itself the tonus has become conspicuous, and the stronger hunger con- 

 tractions usually begin to appear. Superimposed -upon those of the 

 tonus rhythm, hunger pangs may appear in man when the stomach still 

 contains traces of food. 



Fig. 167. Tracing of the tonus rhythm of the stomach (man) three hours after a meal. (From 



Carlson.) 



By studying -the shadow of the outline of the stomach produced by 

 having a person or animal swallow two balloons, one inside the other 

 and with a paste of bismuth subnitrate between them, it has been ob- 

 served that the weaker type of hunger contraction begins as a con- 



Fig. 168. Tracings from the stomach during the culmination of a period of vigorous gastric hunger 

 contractions. One-half original size. (From Carlson.) 



striction involving the cardiac end of the stomach, and moving toward 

 the pyloric end as a rapid peristaltic wave. When the contractions are 

 very vigorous, this wave spreads so rapidly over the stomach that it is 

 difficult to determine whether it really occurs as a very rapid peristalsis 

 or as a contraction involving the fundus as a whole. These contractions 



