GASTRIC DIGESTION 139 



amount of hydrochloric acid varied to any considerable degree from this 

 value a condition of hypoacidity or hyperacidity was said to be es- 

 tablished. On the basis of more recent experiments, 1 however, it 

 appears that the actual acidity of the gastric juice of man as secreted 

 by the glands is 0.4 to 0.5 per cent hydrochloric acid. Boldyreff be- 

 lieves that this acidity is lowered to about 0.2 per cent by regurgitation 

 of alkaline fluid from the intestine (Chapter VIII on Gastric Analysis) . 

 Hydrochloric acid has the power of combining with protein substances 

 taken in the food, thus forming so-called combined hydrochloric acid. 

 This combined acid is a less potent germicide than free hydrochloric 

 acid and has less power to destroy the amylolytic enzyme salivary 

 amylase (ptyalin) of the saliva. This last fact explains to a degree the 

 possibility of the continuance of salivary digestion in the stomach. 



The term combined hydrochloric acid is really a misnomer. When 

 free hydrochloric acid is treated with a protein the latter functions as 

 a base and a salt is formed. Therefore, instead of having "com- 

 bined hydrochloric acid" we have a protein salt of hydrochloric acid. 

 This salt ionizes differently from the free acid. This fact explains the 

 variation in the germicidal properties of the two solutions as well as 

 their different action toward enzymes, such, for example, as salivary 

 amylase (see page 60) . 



The hydrochloric acid of the gastric, juice forms a medium in which 

 the pepsin can most satisfactorily digest the protein food, and at the 

 same time it acts as an antiseptic or germicide which prevents putre- 

 factive processes in the stomach. It also possesses slight power of in- 

 verting cane sugar, this property being due to the hydrogen ion. When 

 the hydrochloric acid of the gastric juice is diminished in quantity 

 (hypoacidity) or absent, as it may be in many cases of functional or 

 organic disease, there is no check to the growth of micro-organisms in 

 the stomach. There are, however, certain of the more resistant spores 

 which even the normal acidity of the gastric juice will not destroy. A 

 condition of hypoacidity may also give rise to fermentation with the 

 formation of comparatively large amounts of such substances as lactic 

 acid and butyric acid. 



The question of the origin of the hydrochloric acid of the gastric 

 juice is a problem to whose solution many investigators have given 

 much attention. Many theories have been proposed, among them the 

 interaction of sodium chloride with carbonic acid, 2 with acid phosphate 8 

 x Babkin: Die aussere Sekretion der VerdauungsdrUsen, Berlin, 1914, p, 113. 

 Boldyreff: Quart. Jour. Exper. Physiol., 8, i, 1914- 

 Carlson: Am. Jour. Physiol., 38, 248, 1915. 

 'Bunge: Physiologic and Pathologic Chemistry, 2nd. Eng. Ed., Philadelphia, 1902, p. 



a Maly: Zeit. f. physioL Chem., i, 174, 1877. Macallum and Collip: Reported before 

 the Society of Biological Chemists, Boston, Dec. 27, 1915. 



