DIGESTION OF FOOD: THE (ESOPHAGUS 93 



blood that flows around them, and pour it into the cavity 

 of the gland, whence it flows into the stomach. 



COMPOSITION AND ACTION OF THE GASTRIC JUICE 



Water makes up over 99% of the gastric secretion. Of 

 the remainder 0.3% is pepsin, 0.2% hydrochloric acid and 

 0.1% sodium chloride (common salt). Less in quantity, but 

 important, are the two ferments rennin and gastro-lipase : 

 The work of the gastric juice is two-fold. 1. It softens 

 the solid foods, which are consequently easily broken up into 

 shreds by the active churning motion of the stomach. Meat, 

 for example, is made up of great numbers of little fibres 

 bound together into a solid mass by connective tissue. This 

 tissue is dissolved away by the gastric juice, thus setting 

 free the fibres and allowing the liquids to act further on 

 each separate fibre. The fat of the meat is also set free from 

 the masses in which it is swallowed, and is melted by the 

 heat of the body into oil. This softening action is performed 

 chiefly by the acid and water of the gastric secretion, not by 

 the pepsin. 



We shall presently see that all foods are digested in the 

 intestine even more vigorously than in the stomach. But 

 stomach digestion is a very important factor, for while the 

 proteids themselves can be acted on in the intestine, the 

 connective tissue that holds the muscle fibres together, will 

 be less quickly dissolved there because of the absence of acid 

 in the intestinal secretions. Without the influence of the 

 gastric juice the muscle fibres will not be readily set loose 

 so that the juices may act upon them. " Stomach digestion" 

 is thus an important preliminary to " intestinal digestion. " 



2. Gastric juice produces a great chemical change in the 

 proteids. Strange as it may seem at first sight, these very 

 important foods, of which meats, milk and eggs are typical 

 examples, cannot be taken through the wall of the intestine, 

 into the blood or be of any use to us unless they first cease 



