248 THE DIGESTIVE SYSTEM 



taken with the patient in the erect posture, the presence of 

 the pylorus at the level of the first lumbar vertebra indicates 

 that it is prevented from descending by pathological adhesions, 

 and suggests the possibility of ulceration in the pyloric region. 

 It may be found that, although the stomach at first assumes 

 a typical J-shape, after a time its shape becomes very indefinite, 

 and, as the two limbs disappear, the bismuth which they 

 contain descends to the same horizontal level (Fig. 95). 

 This appearance indicates a loss of tone in the muscular wall 

 of the stomach, for, although at first able to support a higher 

 column of bismuth in the long limb of the J, the muscle tonus 

 soon becomes fatigued and gives way. 



The Gastric Secretion is intended to act mainly on proteids. 

 Its most important constituents are pepsin and hydrochloric 

 acid, and it should be observed that pepsin can carry out its 

 proteolytic action only in an acid medium. Consequently 

 when pepsin is administered in gastric disorders, it should be 

 combined with an acid solution. Some of the hydrochloric 

 acid is required to neutralise the alkalinity of the saliva which 

 is swallowed with the food, while some of it combines with the 

 proteins of the food. As a result, the amount of free hydro- 

 chloric acid is very small and is no real indication of the 

 amount secreted. 



In addition, the gastric mucosa secretes an enzyme, termed 

 rennin, which has a special curdling action on milk. It acts 

 on the casein, which is the principal proteid in milk, and 

 converts it into an insoluble solid. This solid substance is 

 apparently more readily acted on by pepsin than the soluble 

 casein. It may be pointed out that if the milk is lacking in 

 lime salts the action of the enzyme is seriously interfered with. 



Lactic acid may be present in gastric contents, but it is a 

 product of carbohydrate decomposition and is not secreted by 

 the gastric mucosa. 



In children the hydrochloric acid is relatively less in amount 

 than it is in the adult, and consequently the gastric juice is 

 not so strongly germicidal. 



