46 
CURT P. RICHTER 
stomach. In frogs for instance the stomach happens to be 
so constructed that it is able to adapt itself to very large 
quantities of food. This animal gets its food only at rather 
great intervals—weeks or months—but then usually in a single 
large quantity, other smaller frogs or the like, which take many 
days to be digested. What is the relation between this kind of 
a stomach and the spontaneous activity of the animals? The 
human stomach on the other hand is so constructed that it is 
able to take only relatively small quantities of food at one time, 
but this food is digested almost immediately. A study also of 
the relation of activity to the action of the stomach should be 
very interesting in ruminants where the stomach is made up of 
several separate parts. What does the animal do spontaneously 
during the function of each of these parts? 
There is still another point which argues very strongly for the 
prime importance of the stomach with relation to the other in¬ 
ternal organs especially the bladder and rectum, in bringing about 
about activity. This is the fact that in all animals, and in man 
living in the wilds, distention of the bladder and the rectum is 
relieved wherever the individual happens to be while the con¬ 
tractions of the stomach can only be relieved by movements of 
the organism about in the environment until contact with food is 
actually made and the food is ingested. 
In light of this explanation some of the results obtained in 
earlier chapters especially from the work on the distribution curve 
of activity may now be discussed again. It will be recalled that in 
these experiments it was shown that when the animal is fed just 
once per day and under conditions of constant illumination and 
temperature the spontaneous activity is distributed over the 
twenty-four hours in a very definite way (see figure 6). The form 
of the activity distribution curve was shown to depend on the time 
of the last feeding. The two phases of inactivity and the single 
period of intense activity shown in this curve may be explained 
on the basis of the formulation given above in the following way. 
The first period of inactivity immediately after the daily meal 
occurs at a time when the processes of digestion are going on in 
the stomach and when the hunger contractions are absent. After 
the stomach empties the hunger contractions begin again and 
