THE ACID OF THE GASTRIC JUICE. 351 



much saliva, as the total solids and amount of acid are much less than those 

 usually found. Analyses II. and III. are of dog's saliva. Analysis II. gives 

 the mean of ten determinations, in the case of a dog in which all the salivary 

 ducts had been ligatured. Analysis III. gives the mean of three, in the case of 

 a dog with normal salivary glands. Analysis IV. is that of the gastric juice 

 of a sheep. 



The acid of the gastric juice. The acid of the gastric juice 

 has probably given rise to more discussion than any other subject in 

 physiological chemistry. The principal points for consideration are 

 (a) the nature of the acid ; (&) the seat of formation and the mode of 

 origin of the acid ; (c) the function of the acid. 



The nature of the acid. Before discussing this question in detail, 

 it may be well to state clearly the present state of opinion on the 

 subject. 



It has been demonstrated that hydrochloric acid is the principal acid 

 of the gastric juice, and that in the purer samples free from food it is 

 always present, and is almost exclusively the only acid present ; while in 

 gastric juice mixed with food, especially with carbohydrate food, it may 

 be, and often undoubtedly is, accompanied by lactic acid. C. Schmidt, 

 from a large number of painstaking and laborious analyses, concluded 

 that the pure gastric juice of carnivora, obtained after a fast of eighteen 

 to twenty hours, contains only hydrochloric acid, and no trace of lactic or 

 acetic acids ; while the gastric juice of herbivora contains, besides hydro- 

 chloric acid, small quantities of lactic acid, but this is even then probably 

 from remnants of carbohydrate food. 1 



Prout, 2 in 1824, first showed that gastric juice contains free hydro- 

 chloric acid by the following method : 



The contents of a stomach were mixed up with water, and, after the 

 mixture had settled, the clear part was removed by decantation. This 

 was divided into three equal portions, a, &, and c. 



(a) The first portion was evaporated to dryness, incinerated, and the 

 total amount of chlorine in the ash determined by weighing, as silver 

 chloride. 



(&) The second portion was first made alkaline by the addition of 

 potash, then evaporated to dryness, incinerated, and the total chlorine 

 determined as before. 



(c) In the third portion, the total acidity was determined by titration 

 against standard alkali, and reckoned as hydrochloric acid. 



In portion (a) all the free acid is driven off as well as any which may 

 be combined with volatile or decomposable bases (such as ammonium 

 chloride) ; in portion (&) all the chlorine remains, that which was either 

 free or combined with ammonia becoming converted into non-volatile 

 potassium chloride ; therefore the difference of (&) and (a) gives the free 

 hydrochloric acid, plus any volatile chlorides which may be present. In 

 (c) all the acid is estimated as hydrochloric acid, and by subtracting 

 this from the difference of (I) and (a) the amount present as volatile 

 chlorides is obtained. 



Prout also showed that when gastric juice is distilled, towards the 



1 The stomach of the herbivora retains food for a ranch longer period than that of 

 carnivora. Traces of food are usually found in the stomach of the sheep even thirty-six 

 hours after a meal. See Cl. Bernard, "Lemons de physiol. expe*r." 1856, tome ii. p. 

 389. 



2 Phil. Trans., London, 1824, part i. p. 45. 



