420 ALIMENTARY CANAL 



Secretion of Acid and of Alkali. 



According to Carlson, the total amount of gastric juice secreted 

 by a man with a gastric fistula (on an ordinary diet of meat, bread, 

 vegetables, coffee or milk and fruit) is about 700 c.c. per meal. 

 Somewhere about 2,500 c.c. of water with sufficient hydrochloric 

 acid to make about a 0-03 N solution is secreted per day. This 

 concentration of a mineral acid is greater than is apparently 

 compatible w^ith life, and yet it exists in contact with the stomach 

 wall. Further, the blood from which the acid undoubtedly comes 

 is practically neutral {pH = 7-4). How% then, do the cells of the 

 acid-secreting glands cause the separation of this strong acid from 

 its salts and, having made the acid free, how do they maintain their 

 integrity ? 



(1) Where is the acid formed ? After intravenous injection of 

 solutions of potassium ferrocyanide and of some inert salt of iron 

 which will combine with the ferrocyanide to form Prussian blue 

 only in the presence of free mineral acid, a blue colour is found in 

 certain of the parietal cells. This seems to point to the presence 

 of free mineral acid in these cells, but imfortunately for this 

 thesis, some cells known to be secreting HCl, do not stain, while 

 others incapable of forming HCl {e.g. liver, blood cells, etc.) do 

 stain. 



(2) How is the acid formed ? The present view is that the protein 

 chlorides of the blood are dissociated slightly, as we have seen. 

 Some of the free chlorions pass into the parietal cells and are seized 

 upon by a weak base like ammonium. This weak chloride is 

 secreted by the cells into the lumen of the gland where, meeting 

 water, it is dissociated on the cell-lumen interface. The weak 

 base passes back into the gland cells, and the strong [Cl]~ vmites 

 with some [H|^ from the water and passes into the stomach as HCl. 

 It is known that cells, in contact with NH4CI and H2O, can carry 

 out such a chemical shuffling. For example, the mould Penicilliiim 

 glaucum readily absorbs the anmionia from a solution of ammonium 

 chloride, leaving hydrochloric acid. Evidence in support of this 

 view is afforded by chemical analyses of tissues which show that 

 while all contain ammonium salts those of the mucosa of the 

 stomach contain the highest percentage. We have also seen 

 (Chap. XXIII.) that there exists in blood a definite ratio between 

 [protein HCl] and [NaCl], so that any decrease in the [protein HCl] 

 will lead to a dissociation of (NaCl] to preserve the balance (see 

 also Donnan Equilibrium, Chap. XI.) A disturbance like this 

 has far-reaching effects (see alignment chart, Fig. 83). 



When HCl is secreted there will remain an excess of base in the 

 blood, hence, the denominator of the ratio HaCOg/NaHCOg tends 



