CH. XXXI.] 



THR GASTRIC GLANDS. 



481 



derived from the interaction of thedi-sodium hydrogen phosphate 

 and the carbonic acid of the blood, thus : 



NajHPO, + CO, + H 2 = NaHC0 8 + NaH 2 P0 4 . 



But, as Professor Gamgee has pointed out, these reactions can 

 hardly be considered to occur in the blood generally, but rather 

 in the oxyntic cells, which possess the necessary selective powers 

 in reference to the saline constituents of the blood, and the hydro- 

 chloric acid, as soon as it is formed, passes into the secretion of 

 the gland in consequence of its high power of diffusion. 



Composition of Gastric Juice. 



The following table gives the percentage composition of the 

 gastric juice of man and the dog : 



One sees from this how much richer in all constituents the 

 gastric juice of the dog is than that of man. Carnivorous 

 animals have always a more powerful gastric juice than other 

 animals ; they have more work for it to do ; but the great contrast 

 seen in the table is, no doubt, partly due to the fact that the 

 persons from whom it has been possible to collect gastric juice 

 have been invalids. In the foregoing table one also sees the 

 great preponderance of chlorides over other salts : apportioning 

 the total chlorine to the various metals present, that which 

 remains over must be combined with hydrogen to form the free 

 hydrochloric acid of the juice. 



Pepsin stands apart from nearly all other ferments by requiring 

 an acid medium in order that it may act. Probably a compound 

 of the two substances, called pepsin-hydrochloric acid, is the 

 really active agent. Other acids may take the place of hydro- 

 chloric acid, but none act so well. Lactic acid is often found in 



K.P. 



i i 



