76 NUTRITIONAL PHYSIOLOGY 



cause a second gaping of the sphincter, followed as before 

 by prompt and decisive contraction. A more efficient 

 mechanism to insure gradual delivery to the intestine 

 without distending it locally can scarcely be conceived. 

 When the latest portions of a meal are leaving the stomach, 

 the first which went out may have reached the colon, and 

 intermediate fractions may be undergoing digestion in 

 numerous loops of the intervening small intestine. 



Our meals are usually of a mixed character, including 

 proteins, fats, and carbohydrates. For purposes of experi- 

 ment single food-stuffs may be fed to an animal and the 

 rate of departure from the stomach noted for each. The 

 x-ray has been employed for this purpose. Carbohydrates 

 have a striking tendency to escape rapidly to the intestine. 

 The discharge of proteins and of fats is relatively much de- 

 layed. We must be content with stating the fact without 

 undertaking to discuss its somewhat complex causes. 



Vomiting. The occasional expulsion of the stomach- 

 contents through the cardia and esophagus is accomplished 

 as the result of a reflex movement in which the chief mus- 

 cles involved are not the coats of the stomach, but the 

 contractile tissue of the diaphragm and abdominal wall. 

 When these contract simultaneously a high pressure is 

 thrown upon the stomach. Such a pressure may accom- 

 pany the act of straining or bracing the body for lifting, 

 but does not ordinarily result in vomiting, it would appear, 

 because of the resistance offered by the cardiac sphincter. 

 In the crisis of nausea, however, convulsive movements 

 of this kind take place with inhibition of the sphincter. 

 With the passage open, each application of intense pressure 

 to the stomach may drive a portion of its contents to the 

 exterior. The palate meanwhile has assumed the same 

 position as for swallowing; the larynx is drawn forward and 

 is shielded by the root of the tongue, which is depressed and 

 grooved. At every descent of the diaphragm the capacity 

 of the thorax is increased, and as no air is permitted to 

 enter the lungs the esophagus is dilated. 



During the act of vomiting the fundus is said to contract 



