DIGESTION 115 



The secretion by the gastric glands of so powerful a mineral 

 acid as hydrochloric has always aroused interest. How is it 

 possible for the gland-cells to produce it without injury to them r . 

 selves, or for the stomach to contain it without self-digestion ? v 

 Many chemical and physical theories have been advanced in 

 the belief that they rendered the process of its production less 

 difficult to understand. All such theories are, however, in- 

 adequate to explain the secretion as a discontinuous process, 

 which occurs only as a response to demand. That the source 140 

 of the acid is the sodic chloride which the gland-cells take from v 

 the blood does not need assertion, but we cannot picture the 

 process by which this exceedingly stable compound is decom- 

 posed otherwise than on the assumption that weaker acids, 

 or, rather, acid salts, are also absorbed by the cells, and that, 

 in accordance with the laws which govern the composition of 

 salts in solution, an exchange of acids occurs. If sodic chloride 

 and any acid salt acid phosphate of sodium, for example 

 are in solution in water, the salts do not retain their form as 

 we know them when isolated by crystallization. The mixture 

 contains "J^ee " hydrochloric as well as " free " phosphoric 

 acid. It may be assumed that within secreting cells a similar 

 exchange of acids takes place. By a process which we term 

 " vital," the acids are kept apart, and the hydrochloric acid is 

 extruded by the cells. In the present state of knowledge this 

 vital action is mysterious ; but it is no more mysterious than 

 the isolation of pepsin, or any other metabolic event which 

 occurs within a cell. 



The proteolytic ferment pepsin is active only in an acid 

 medium. Yet apart from its digestive function as an ally of 

 pepsin, hydrochloric acid by itself also exerts a valuable 

 disintegrating action on certain constituents of the food. 

 Possibly the most important results of the presence of free 

 hydrochloric acid in the great chamber into which food is first 

 received are due to its disinf ective property. It destroys all the 

 putrefactive germs which accompany the food, and many germs 

 which, if introduced into the blood, would give rise to disease. 

 It also destroys the germs which multiply in the stomach 

 towards the end of each interval between two meals. When 

 withdrawn from the body, gastric juice will keep an indefinite 

 time, if evaporation of the acid be prevented. 



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