124 THE DIGESTIVE FLUIDS. 



tillate, which is received in a high Erlenmeyer flask, is heated with 

 20 c.c. of a y 1 ^ normal solution of iodine and the same amount of a 

 5.6 per cent, solution of potassium hydrate. The mixture is thor- 

 oughly shaken and set aside for a few minutes. The excess of 

 iodine is then estimated after adding 20 c.c. of hydrochloric acid 

 (specific gravity 1.018), by titrating with a -fa normal solution of 

 sodium tliiosulphate. The titration is carried almost to the point of 

 decolorization, when a little starch solution is added, and the titra- 

 tion continued until the last trace of blue has disappeared. The dif- 

 ference between the number of cubic centimeters of the tliiosulphate 

 solution employed to bring about this end and the amount of the iodine 

 solution added, viz., 20, will indicate the number of cubic centimeters 

 of the latter which were utilized in the formation of iodoform. Bv 

 multiplying this number by 0.003388 the corresponding amount 

 of lactic acid is ascertained. 



Quantitative Estimation of the Organic Acids. The organic acids 

 in toto may be estimated by one of the methods already described 

 (pages 120 and 121), or according to the following procedure, as 

 suggested by Hehner-Seemann. This method is based upon the 

 transformation of the organic acids into their alkaline salts, and 

 their subsequent combustion, with the formation of the correspond- 

 ing carbonates, which are then estimated by titration. At the same 

 time the amount of physiologically active hydrochloric acid can be 

 obtained as follows : 10 c.c. of the filtered gastric contents are neu- 

 tralized with a decinormal solution of sodium hydrate, and the total 

 acidity thus ascertained. The neutralized solution is then evaporated 

 to dry ness and the residue incinerated. Care should be had, however, 

 that the application of heat is discontinued as soon as the ash has 

 ceased to burn with a luminous flame. The residue is then taken up 

 with a small amount of water and titrated with a decinormal solution 

 of hydrochloric acid. The number of cubic centimeters employed to 

 bring about the end-reaction, multiplied by 0.00365, will indicate 

 in terms of hydrochloric acid the amount of organic acids which were 

 originally present. By deducting this value from the total acidity, 

 as first ascertained, the amount of physiologically active hydro- 

 chloric acid is found. 



The Ferments of the Gastric Juice and their Proenzymes. 



In the gastric juice of almost all vertebrate animals two fer- 

 ments are constantly found. These are termed pepsin and chy- 

 mosin, or rennin, and are supposedly furnished by the so-called 

 addomorphous or central cells of the gastric glands. This has been 

 established by resecting the pyloric end of the stomach and convert- 

 ing. it into a blind pouch, with a fistulous opening on the anterior 

 abdominal walls, while the fundus was united to the duodenum. It 

 was then noted that this resected portion of the stomach, in which 

 no delomorphous cells are found, furnished an alkaline and markedly 



