688 PHYSIOLOGY OF DIGESTION AND SECRETION. 



cells of the gastric tubules constitute the acid-secreting cells. This 

 belief is founded upon the general fact that in the regions in which 

 these cells are chiefly present that is, the middle region of the 

 stomach the secretion is distinctly acid, and where they are absent 

 or scanty in number the secretion is alkaline or less acid. In the 

 pyloric region, for instance, these cells are lacking entirely and the 

 secretion is alkaline. So also in the fundus the secretion does not 

 seem to be acid, and this fact corresponds with a marked diminution 

 or absence of the border cells. With regard to the origin of the acid 

 it is evident that it is formed in the secreting cells, since none exists in 

 the blood or lymph. It seems also perfectly evident that the HC1 

 must be formed from the chlorids of the blood. The chief chlorid 

 is NaCl and by some means this compound 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, 

 toge her 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, accord- 

 ing to the formula NaH 2 P0 4 + NaCl = Na 2 HP0 4 + HC1. Other 

 theories have been proposed, but, as a matter of fact, no explanation 

 of the details of this reaction is satisfactory. We must be content 

 to say that in the acid-forming cells the neutral chlorids (NaCl) are 

 broken up with the formation of free HC1. 



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.* 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 

 make separate fistulous openings to the exterior. Under these con- 

 ditions, when the animal ate and swallowed food it was discharged 



* See Pawlow, " The Work of the Digestive Glands, " translated by 

 Thompson, 1902. 



