774 .PHYSIOLOGY OF DIGESTION AND SECRETION. 



pound is broken up; the chlorin is combined with hydrogen, and 

 is then secreted upon the free surface of the stomach as HC1. 

 In support of this general statement it has been shown that if the 

 chlorids in the blood are reduced by removing them from the food 

 for a sufficient time the secretion of gastric juice no longer contains 

 acid. On the other hand, addition of NaBr or KI to the food may 

 cause the formation of some HBr and HI, together with HC1 in 

 the gastric juice. Maly has suggested that acid phosphates may 

 be produced in the first instance, and then by reacting with the 

 sodium chlorid may give hydrochloric acid, according to the formula, 

 NaH 2 PO 4 + NaCl = Na 2 HPO 4 + HC1. Other theories have been 

 proposed, but, as a matter of fact, no explanation of the details 

 of this reaction is satisfactory. Many observers have attempted 

 by microchemical methods to determine the exact points in the 

 gastric glands at which the acid is formed. Most of these attempts 

 have given results which have been difficult to interpret. Harvey 

 and Bensley,* by making use of dyes (cyanimin and neutral red) 

 which give different colors in neutral, alkaline, and acid media, 

 state that the free acid is found only on the internal surface of the 

 stomach or in the neck of the glands. The parietal cells themselves 

 exhibit an alkaline reaction. These observers advance, therefore, 

 the probable hypothesis that the parietal cells secrete a chlorid 

 of an organic base, and this compound in some way yields free 

 hydrochloric acid only after it reaches the mouth of the gland. 

 While the ultimate source of the chlorin of the hydrochloric acid 

 is to be found in the neutral chlorids of the blood (NaCl), certain 

 as yet unknown intermediate compounds are formed within the 

 parietal cells from which the acid is eventually produced. 



The Secretory Nerves of the Gastric Glands. Although several 

 facts indicated to the older observers that the secretion of gastric 

 juice is under the control of nerve fibers, we owe the actual experi- 

 mental demonstration of this fact to Pawlow. f He demonstrated 

 that the secretion is under the control of the nervous system and that 

 the secretory fibers are contained in the vagus. Direct stimulation 

 of the peripheral end of the cut vagus causes a secretion of gastric 

 juice after a long latent period of several minutes. This long latency 

 may be due possibly to the presence in the vagus of inhibitory 

 fibers to the gland, which, being stimulated simultaneously with the 

 secretory fibers, delay the action of the latter. Very striking proof 

 of the general fact that the secretion is due to the action of vagus 

 fibers is furnished by such experiments as these : Pawlow divided the 

 esophagus in the neck and brought the two ends to the skin so as to 



* Harvey and" Bensley, "Biological Bulletin," 23, 225, 1912. 

 t See Pawlow, "The Work of the Digestive Glands," translated by Thomp- 

 son, 1902. 



