In the transfer of food from the stomach to the intestine two factors are concerned, the gastric waves of peristalsis and the pyloric sphincter. It is now known that under normal conditions the peristaltic waves course from the middle of the stomach to the pylorus without interruption during the whole of a digestive period. How the waves will affect the food is determined by the action of the pylorus. If the pylorus remains closed, the repeated waves over and over again churn the food with the gastric secretions; if the pylorus opens, these same waves act as the motive power to force the food onward.
The determinative function of the pylorus was recognized by the fathers of medicine, for they gave the ancient terms pylorus (keeper of the gate), rector and janitor to the sphincter, and assumed that it possessed a "will" which fixed the fate of ingested food. Van