THE GASTRIC JUICE. 135 



is treated with a little sulphuric acid and alcohol. The reaction is 

 due to the formation of ethyl butyrate, C 4 H 7 O 2 .C 2 H 5 . 



Quantitative Estimation of Lactic Acid. This is best accom- 

 plished by means of Boas' method: The decomposition of the lactic 

 acid is effected as described above. After the addition of the sul- 

 phuric acid and manganese dioxide the flask is closed with a doubly 

 perforated stopper. Through one aperture a bent tube passes to the 

 condenser, while a straight tube passes through the other opening, 

 and is provided at its free end with a small piece of rubber tubing 

 that is clamped ; this tube should dip well into the liquid, and serves 

 for passing a current of air through the solution when the distilla- 

 tion is completed. The mixture is then distilled until about four- 

 fifths of the contents have passed over, excessive heat being carefully 

 avoided, so as to prevent decomposition of the aldehyde. The dis- 

 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 y 1 ^ normal solution of 

 sodium thiosulphate. 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 thiosulphate 

 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. By 

 multiplying this number by 0.003388 the corresponding amount 

 of lactic acid is ascertained. 



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 

 adelomorphous 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 remaining portion of the stomach was 

 united to the duodenum. It was then noted that this resected por- 

 tion of the stomach, in which no delomorphous cells are found, fur- 

 nished an alkaline and markedly viscid secretion, which contained 

 pepsin and large amounts of mucin, but no hydrochloric acid. A 

 reversal of the experiment, in which the middle portion was thus 

 isolated, showed that here both pepsin and hydrochloric acid are 

 secreted. As this portion of the stomach contains both delomor- 

 phous and adelomorphous cells, the conclusion naturally suggested 

 itself that the hydrochloric acid is furnished by the delomorphous 



