510 



THE GASTRIC JUICE 



[CH. XXX11I. 



The parietal cells undergo merely a change of size during secre- 

 tion, being at first somewhat enlarged, and after secretion they are 

 somewhat shrunken. They are also called oxyntic (acid -forming) cells, 

 because they secrete the hydrochloric acid of the juice. Heidenhain 

 succeeded in making in one dog a cul-de-sac of the fundus, in another, 

 of the pyloric region of the stomach; the former secreted a juice 

 containing both acid and pepsin ; the latter, parietal cells being 

 absent, secreted a viscid alkaline juice containing pepsin. 



The formation of a free acid from the alkaline blood and lymph 

 is an important problem. There is no doubt that it is formed from 

 the chlorides of the blood and lymph, and of the many theories 

 advanced as to its actual mode of formation, none is wholly satis- 

 factory. Some theories are chemical, and explain the formation of 

 the acid by an interaction of the chlorides and phosphates. Others 

 call to their assistance the law of " mass action," and we certainly 

 know that by the action of large quantities of carbonic acid on salts 

 of mineral acids, the latter may be liberated in small quantities. We 

 know further that small quantities of acid ions may be continually 

 formed in the organism by ionisation. But in every case we can 

 only make use of these explanations if we assume that the small 

 quantities of acid are carried away as soon as they are formed, and 

 thus give room for the formation of fresh acid. Even then we are 

 unable to explain the whole process. A specific action of the cells is 

 no doubt exerted, for these reactions can hardly be considered to 

 occur in the blood generally, but rather in the oxyntic cells, which 

 possess the necessary selective powers in reference to the saline 

 constituents of the blood, and the hydrochloric acid, as soon as it is 

 formed, passes into the secretion of the gland in consequence of its 

 high power of diffusion. 



Composition of Gastric Juice. 



The following table gives the percentage composition of the gastric 

 juice of man and the dog: 



