140 THE A&DOMEN. 



minutes after the appearance of food there is no hydro- 

 chloric acid present and, the food being alkaline, salivary 

 digestion continues. Then, called forth by the presence 

 of the food, the hydrochloric acid appears and salivary 

 digestion ceases in the acid medium. Little digestion 

 of starches or fats takes place, the chief action being on 

 proteins, which are converted into soluble peptones. 

 For besides hydrochloric acid the gastric juice contains 

 two ferments: 1. pepsin, which is particularly active in 

 aiding the digestion of proteins, and 2. rennin, which 

 especially affects milk. Neither hydrochloric acid nor 

 pepsin seems capable of digesting food alone, but each 

 is essential to the other. They are secreted by different 

 types of cells, secretion depending upon the nerve supply 

 and upon the presence of food. Gastric digestion is 

 favored by minute subdivision of the food and by the 

 right proportion of hydrochloric acid, which should be 

 0.2 per cent. Body temperature is also advantageous. 

 Except that proteins are put in solution and partly di- 

 gested, little digestion goes on in the stomach, and though 

 the rugae afford a large absorbing surface, little absorption 

 takes place, although more takes place than in the mouth 

 and in time most foods, except fats, can be absorbed. 

 The time of digestion varies with different foods and in 

 different poeple, but probably three to five hours are 

 necessary. The food leaves the stomach as chyme, a 

 fluid of about the consistency of pea soup. 



Vomiting is more or less the reverse of swallowing and 

 is generally preceded by a feeling of nausea, which starts 

 up retching, a more or less involuntary effort of the stom- 

 ach to throw off its contents. To relieve the retching a 

 long breath is taken, followed by a deep expiration that 

 opens the cardiac end of the stomach and allows the 

 abdominal muscles to force the food out. After much 

 vomiting and prolonged retching the pyloric end of the 

 stomach may be affected and bile will then appear in the 

 vomitus. Artificial vomiting may be produced by irrita- 



