Like the stomach of the herbivora in general, the various divisions of the stomach in the ruminants are probably never completely empty of food. Digestion in these animals is therefore a more or less continuous process, and if they eat because feeling hunger, they must b^ capable of experiencing hunger with the stomach partly filled with food, and while the blood is still receiving a constant stream of digested pabulum from the small intestines.
By a balloon method and with a fistula in the rumen, Dr. Schalk and the writer studied the contractions of this stomach pouch in the goat. We started the work on the rumen, as this corresponds to the cardiac or fundus part of the stomach of other mammals, and is, therefore, probably the region most directly concerned with the causation of hunger.
The body of the rumen of the goat exhibits strong periodic contractions, independent of those concerned with the regurgitation of the food bolus into the mouth, i.e., the act of rumination. The contractions vary in intensity, but appear to be practically continuous; that is, there appears to be no period of real quiescence. When the goat is starved for several days or the greater part of the food in the rumen is removed through the fistula, these contractions become stronger without much change in rate. So far, observations have been made only on the rumen of one goat, but the motor conditions found are essentially similar to those already described in the rabbit and the guinea-pig. The digestion contractions of the filled rumen pass gradually into the stronger contractions of the empty or partly empty rumen. We may provisionally call the latter "hunger contractions," assuming that it is the partly empty rumen that gives the impetus to feed. So far as we know the only difference between the completely filled and the partly empty rumen is this difference in tonus and strength of contraction. There is no gastric juice secreted in the rumen, hence there is no acidity except that due to the action of bacteria, and there is no regurgitation of the acid content of the true stomach (abomasum) into the rumen. Unless we assume with J. Muller that the sensation of hunger is purely negative, or due to the absence of satiety, the hunger in the ruminant must in some manner be associated with these powerful contractions of the partly empty rumen.