SECRETIONS 97 



The isolated pyloric end of the stomach secretes a gastric juice 

 which is not acid. As the ovoid cells are lacking in this part, it 

 is supposed that the hydrochloric acid is secreted by these cells. 



The morphological changes during the activity of the 

 cells are as follows: The chief cells, which are large and 

 granular during fasting, at first become still larger, but from 

 the sixth to the ninth hour of digestion they become smaller 

 and clearer. The ovoid cells, small during fasting, are much 

 enlarged during digestion. 



Concerning the origin of the characteristic constituents of 

 gastric juice, nothing is known for certain. Both ferments must, 

 however, be regarded as a product of the gland-cells. 



As to the formation of the hydrochloric acid it is difficult to 

 understand how a free strong acid can originate while the blood 

 and the secretory cells have an alkaline reaction. An explanation 

 has been sought in the mass action of weak acids (e.g. carbonic 

 acid) upon the chlorides of the blood. In the same way as 

 hydrochloric acid is set free by the mass action of the carbonic 

 acid of the blood upon sodium chloride and is then taken up by 

 the blood corpuscles (see page 59), the mass action of carbonic 

 acid in the ovoid cells might set free the hydrochloric acid. 



Recently it has been supposed that the acid is not formed in the 

 gland-cells, but is formed from the chlorides of the food in the 

 following manner: 



By dissolving in water a part of the sodium chloride of food is 

 split up into sodium and chlorine ions. The free sodium ions in 

 the stomach are supposed to pass through the walls of the stomach 

 by diffusion in exchange for the free hydrogen ions of the blood. ^/ 

 The walls of the stomach are impermeable to the chlorine ions, 

 hence they remain in the stomach and form, with the hydrogen 

 ions coming from the blood, the hydrochloric acid. This view is 

 based upon the following facts: (i) The cells remain alkaline 

 notwithstanding the acid formation; (2) If chlorides are not 

 present in the stomach, no free acid is supposed to be formed; 

 (3) The alkalinity of the blood and of the urine is increased after 

 the eating of sodium chloride. 



3. Influence of the nervous system on secretion. 



Observations on the secretion of gastric juice can be easily made 

 on men and animals by means of a gastric fistula. 



Gastric secretion begins when food has been swallowed, 

 even when food passes out by an esophageal fistula so that 



