GASTRIC JUICE AND CHANGES IX STOMACH. 1$! 



THE DIGESTIVE AGENTS. 



Origin of the Free Hydrochloric Acid. The material 

 from which the fundus cells produce the enzymes and the acid 

 is the blood. But this is always slightly alkaline and to ac- 

 count for the secretion of a characteristic acid from such a 

 source has long been a puzzle to physiologists. Several hy- 

 potheses have been advanced, but these are all more or less 

 faulty. The difficulty is not with the liberation of hydro- 

 chloric acid, which is a purely chemical question, and one 

 which may now be explained, but with its secretion. 



The blood contains always a small amount of sodium chlor- 

 ide and an excess of carbonic acid. In a solution containing 

 these two things some double decomposition must take place 

 with production of a little free hydrochloric acid and sodium 

 carbonate. According to the older view hydrochloric acid is 

 so much stronger than carbonic acid that the liberation of the 

 former from a chloride by the action of the latter is impos- 

 sible. But this view leaves out of consideration the effect of 

 a much greater mass of the weaker acid through which in fact 

 a dissociation of the chloride is to a certain extent accom- 

 plished. But, granting this kind of a double decomposition 

 it is still beyond our powers to explain how the free acid 

 formed in the cells is able to pass in one direction into the 

 stomach, while the sodium carbonate produced at the same 

 time wanders in the other direction into the blood. 



This acid is not liberated in constant amount at all times 

 but its flow is subject to the influence of the various stimuli 

 referred to above. The quantity present then in the stomach 

 may vary from a mere trace, or zero even, to a maximum. 

 This maximum may be 0.2 or 0.3 per cent of the liquid con- 

 tents. How it is measured will be shown below. Just what 

 is meant by the term free hydrochloric acid will be presently 

 explained. 



The Enzymes. In an earlier chapter the general nature 

 and behavior of the two gastric ferments, the pepsin and ren- 



