476 THE HUMAN BODY 



of course, in the case of a mixed meal, but a meal of pure carbo- 

 hydrates will begin to leave the stomach much sooner after Di- 

 gestion than a meal of pure protein (10-15 minutes as compared 

 with J/2 hour), and will be discharged completely in half the time 

 (2-23/2 hours as against 4-5); and a meal in which the carbohy- 

 drates are eaten before the proteins may show a definite interval 

 between the discharge of the last carbohydrates and the first 

 proteins. The admixture of fats with the other food stuffs delays 

 considerably the rate of discharge. 



The pyloric sphincter does not hold against pure water nor 

 against substances of the consistency of raw egg-white or raw 

 oysters. These, unless mixed with other materials, pass promptly, 

 therefore, from the stomach into the small intestine. 



Importance of the Stomach. Aside from its function of begin- 

 ning the digestion of proteins, a function which, as we have seen 

 (p. 465) is subordinate to the more efficient digestive action of the 

 small intestine, the chief significance of the stomach is that it en- 

 ables us to take our daily supply of food in three meals, more or less, 

 according to our habit. The small intestine is a narrow tube. The 

 ducts of pancreas and liver open into its upper end. If our food 

 when swallowed passed directly into the intestine each mouthful 

 would crowd the preceding ones along at such a rate that no ade- 

 quate admixture with the essential juices of the pancreas and 

 liver could occur, and very little digestion would take place. To 

 avoid this difficulty the food would have to be eaten little by 

 little, and to get enough for the needs of the Body would require 

 hours of steady nibbling. By affording storage to a considerable 

 amount of food, which is automatically passed along to the intes- 

 tine at just the rate at which that region can handle it, the stomach 

 permits us to follow eating habits much less time consuming, and 

 more convenient. 



Movements of the Small Intestine. The food entering the 

 small intestine is subjected to two sorts of movements whose 

 combined effect is to churn it very thoroughly and to move it 

 slowly along the gut so as to make room for more to come in from 

 the stomach. The churning is effected mainly by movements of 

 the intestine known as rhythmic segmentation. In these move- 

 ments rings of the circular muscle coat about an inch apart con- 

 strict simultaneously, splitting the contained food into a series of 



