BEHAVIORISTIC STUDY OF THE RAT 
51 
In order to bring these results into relation with the activity 
of the stomach it is necessary to bring out some additional facts 
regarding the function of the stomach. (1) Each period of 
activity of the stomach begins with small contractions. These 
contractions come with a very regular rate, one every eighteen to 
twenty seconds. For the reason of this rate Carlson speaks of 
these contractions as the “ twenty-second rhythm. ” These 
contractions become larger and larger as the period advances 
without changing their rate. (2) After these contractions have 
reached a certain size, quite abruptly a new series of very 
much larger contractions beings. These larger contractions come 
at a different and irregular rate, and also have a different form. 
These are the so-called “ main hunger contractions. ” Whether 
or not there is any real difference between the small and the large 
Fig. 24. Relation of Stomach Contractions to Activity in Double Cage 
contractions besides what can be explained in terms of the 
different extent to which the musculature of the stomach is in¬ 
volved in the two cases is not definitely known. (3) Cannon 
was the first to show that these large contractions give rise to the 
sensation of hunger and (4) Carlson has shown that the intensity 
of the hunger sensation is roughly proportional to the size of 
the contraction. 
The relation of the results obtained in the 1 double cage’ to 
these facts is brought out in figure 24. In this figure the diffuse 
spontaneous activity in the double cage is shown on the top 
line. The entrances into the food box are shown on the second 
line. The probable relation of the stomach contractions to the 
diffuse activity and to the entrances into the food box is shown 
on the bottom line. The small contractions serve only to stimu¬ 
late the animal to diffuse activity, restlessness. It is not until 
