358 CHEMISTR Y OF THE DIGESTIVE PROCESSES. 



place in solution. He dissolved sodium chloride and lactic acid together 

 in water, placed the solution in the bottom of a cylindrical vessel, and 

 then carefully poured a layer of distilled water on the top. After some 

 days, part of the upper layer was removed and analysed ; it was found to 

 contain more than sufficient chlorine to balance all the sodium present ; 

 that is to say, it contained free hydrochloric acid. Similar results were 

 obtained with a mixture of monosodium phosphate, and other acid salts, 

 in common solution with sodium chloride. 



These results of Thomsen and Maly will be again referred to in 

 discussing the mode of origin of hydrochloric acid. They are introduced 

 here to show that any weaker acids in gastric juice along with the 

 hydrochloric acid must in part be uncombined. Any organic acids 

 present during digestion will also be inj^art free and in part combined, 

 and as these have very small avidities compared with hydrochloric acid, 

 they will be almost completely free. This has a bearing of some import- 

 ance. Any organic acids formed in the stomach by bacterial action on 

 carbohydrates will be found as free acids, and will not reduce the amount 

 of free hydrochloric acid, 1 but salts of organic acids entering the stomach 

 with the food will reduce the amount of acidity due to free hydrochloric, 

 because, from the organic salts, free acids will be formed, by hydrochloric 

 acid combining with their bases. 



Source of the hydrochloric acid. The only possible source of chlorine 

 lies in the chlorides of the food, and from this either directly, or indirectly 

 through the blood, the hydrochloric acid must necessarily have its origin. 

 That the chlorides present in the blood plasma are the source of the acid, 

 has been experimentally proved by Voit 2 and Cahn. 3 



Following a method first used by Yoit, Cahn fed dogs exclusively 

 on meat which had previously had all its salts extracted by boiling it 

 repeatedly with distilled water. An animal fed in this manner continues 

 to excrete a diminishing quantity of chlorides in the urine for a period 

 varying from two to five days. After this only traces of chlorides are 

 found in the urine, but the tissues and blood still cling on to their 

 necessary minimum quantity of chlorides, digestion goes on, and the 

 animal lives. At this period, if the contents of the stomach are washed 

 out with distilled water, the secretion is found to contain free acid and 

 to possess digestive power. If now the animal's reserve stock of chlorine 

 be still further reduced by administering diuretics, such as potassium 

 nitrate, which cause some additional chlorides to be excreted ; or if free 

 hydrochloric acid be repeatedly removed by pumping out the contents of 

 the stomach with the aid of distilled water, a condition is finally reached 

 in which the stomach secretes a completely neutral fluid, which is 

 altogether inactive so long as it is neutral, but quickly digests fibrin if 

 1 part per 1000 of hydrochloric acid be added to it. When this 

 stage is reached the animal rapidly fails ; but if a small quantity of 

 sodium chloride be now given to it, it rapidly recovers, and soon becomes 

 in every respect normal. 



This experiment also shows that the secretion of pepsin is independ- 

 ent of that of acid, and that in the absence of hydrochloric acid no 



1 In fact will slightly increase it by combining to a certain extent with the bases of the 

 chlorides. 



2 Sitzungsb. d. Jc.-bayer. ATcad. d. Wissensch. zu Miinchen, 1869, Bd. ii. S. 483. See 

 also M. Gruber, Bcitr. z. Pliysiol. C. Ludiuig z. s. Geburtst., Leipzig, 1887. 



3 Ztschr. f. physiol Chem., Strassburg, 1886, Bd. x. S. 522. 



