3 o6 THE POPULAR SCIENCE MONTHLY 



2.3 cm. in diameter), registered the periodic oscillations shown in Fig. 

 3. Though individually more prolonged than those of the stomach, 

 these contractions, it will be noted, occur at about the same rate. It is 

 probable that the periodic activity of the two regions is simultaneous, 

 for otherwise the stomach would force its gaseous content into the 

 oesophagus with the rise of intragastric pressure. 



What causes the contractions to occur has not been determined. 

 From evidence already given they do not seem to be directly related 

 to bodily need. Habit no doubt plays an important role. For present 

 considerations, however, it is enough that they do occur, and that they 

 are abolished when food, which satisfies bodily need, is taken into the 

 stomach. By such indirection, as already stated, are performed some 

 of the most fundamental of the bodily functions. 



Peculiarities of Hunger Explained by Contractions. — If these con- 

 tractions are admitted as the cause of hunger, most of the difficulties 

 confronting other explanations are readily obviated. Thus the occur- 

 rence of hunger at meal times is most natural, for, as the regularity of 

 defecation indicates, the alimentary canal has habits. Activity returns 

 at the usual meal time as the result of custom. By taking food regu- 

 larly at a definite hour in the evening for several days, a new hunger 

 period can be established. Since at these times the oesophagus and the 

 empty stomach strongly contract, hunger is aroused. 



The contractions furthermore explain the sudden onset of hunger 

 and its peculiar periodicity — phenomena which no other explanation 

 of hunger can account for. The quick development of the sensation 

 after taking a cold drink is possibly associated with the well-known 

 power of cold to induce contraction in smooth muscle. 



The great intensity of hunger during the first day of starvation, and 

 its gradual disappearance till it vanishes on the third or fourth day, 

 are made quite clear, for Boldireff observed that the gastric contrac- 

 tions in his fasting dogs went through precisely such alterations of in- 

 tensity, and were not seen after the third day. 



In fever, when bodily material is being most rapidly used, hunger 

 is absent. Its absence is understood from an observation reported four 

 years ago, that infection, with systemic involvement, is accompanied 

 by a total cessation of all movements of the alimentary canal. 45 Boldi- 

 reff observed that when his dogs were fatigued the rhythmic contrac- 

 tions failed to appear. Being " too tired to eat " is thereby given a ra- 

 tional explanation. 



Another pathological form of the sensation — the inordinate hunger 

 (bulimia) of certain neurotics — is in accordance with the well-known 

 disturbances of the tonic innervation of the alimentary canal in such 

 individuals. 



45 Cannon and Murphy, Joxirnal of the American Medical Association, 1907, 

 XLIX., p. 840. 



