CH. XXXI.] 



COMPOSITION OF GASTRIC JUICE 



483 



derived from the interaction of the di-sodium hydrogen phosphate and 

 the carbonic acid of the blood, thus : 



Xa 2 HP0 4 + C0 2 + H,O == NaHCO 3 + XaH 2 PO 4 . 



But, as 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 hydrochloric acid, as soon 

 as it is formed, passes into the* 1 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. 



In recent years, the composition and action of the gastric juice 

 has been studied by Pawlow. By an ingenious surgical operation, he 

 succeeded in separating from the stomach of dogs a diverticulum 

 which pours its secretion through an opening in the abdominal wall ; 

 the nerves of this small stomach are intact, and the amount of juice 

 that can be collected from it when it is active amounts to several 

 hundred cubic centimetres in a few hours. Pawlow thus obtained a 

 pure gastric juice, which enabled him to study its action and com- 



