460 DIGESTION 



has no combining power for acids, so that the acid secreted with the 

 psychic juice remains uncombined and on gaining the pyloric vestibule 

 excites the opening of the sphincter. Protein, on the other hand, as is 

 well known, absorbs considerable quantities of free hydrochloric acid, 

 so that for some considerable time after it is taken, none of the acid exists 

 in a free state. Fats owe their slow discharge partly to inhibition of 

 gastric secretion, and partly to the longer time it takes for them to become 

 neutralized in the duodenum, because of the fatty acid split off by the 

 action of lipase. 



Interesting observations have also been made on the rate of discharge 

 when various combinations of foodstuffs were fed. This has been done 

 by feeding one foodstuff before the other, or by mixing the foodstuffs. 

 When carbohydrates were fed first and then protein, the discharge be- 

 gan much earlier than with protein alone, because the carbohydrate food 

 first reached the pyloric vestibule (see page 454). However, at the end 

 of two hours, when the carbohydrate curve should begin to come down, 

 it remained high, indicating that the protein had by this time reached 

 the pylorus and was being discharged at its own rate. When the meat 

 was fed before the carbohydrate, the curve to start with was exactly 

 like that for protein, becoming, however, considerably heightened later 

 when the carbohydrate reached the pyloric vestibule. The presence of 

 protein near the pylorus, therefore, distinctly retards the evacuation of 

 carbohydrate from the stomach. These facts, it will be remarked, all 

 fit in admirably with the observations which we have already detailed 

 concerning the disposition of food in the stomach. 



When mixtures of equal parts of different foods were fed, the results 

 indicated that the emptying of the stomach occurred at a rate which 

 Avas intermediate between those of the foods taken separately. Mixing 

 protein Avith carbohydrate, for example, accelerated the rate at Avhich 

 protein left, and mixing fats Avith protein caused the protein to leave 

 the stomach considerably more sloAvly than if protein alone had 

 been fed. 



Influence of Pathologic Conditions on the Emptying 



An important surgical application of these facts concerns the behavior 

 of food after gastroenterostomy. It has been thought that this operation 

 would cause the food to be drained from the stomach into the intestine 

 and thus leave the region of the stomach betAveen the fistula and the 

 pylorus inactive. This assumption is based on the idea, Avhich AVC have 

 seen to be erroneous, that gravity assists in the emptying of the stomach. 

 As a matter of fact, it has been found that, if the gastroenterostomy is 

 made Avhen there is no obstruction at the pylorus, the chyme takes its 



