Page:Popular Science Monthly Volume 81.djvu/312

306 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 rôle. 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 contractions are admitted as the cause of hunger, most of the difficulties confronting other explanations are readily obviated. Thus the occurrence 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 regularly at a definite hour in the evening for several days, a new hunger period can be established. Since at these times the œsophagus 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 contractions in his fasting dogs went through precisely such alterations of intensity, 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. Boldireff observed that when his dogs were fatigued the rhythmic contractions failed to appear. Being "too tired to eat" is thereby given a rational 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.