ENZYMES AND THEIR ACTION. 19 



The measurements of gastric juice may conveniently be made with 

 a one c.c. pipette which is accurately graduated in /4oo c - c - Into 

 the first tube in the series may be introduced one c.c. of gastric 

 juice, and the tubes which follow in the series may receive vol- 

 umes which differ, in each instance, from the volume introduced 

 into the preceding tube by %oo, %o, %>o, or % of a cubic centi- 

 meter. Now rapidly introduce into each tube the same volume 

 (e. g., 2 c.c.) of a i : 1000 solution of edestin 1 and place the tubes 

 at 40 C. for one-half hour. At the end of this time stratify 

 ammonium hydroxide upon the contents of each tube, 2 place the 

 tubes in position before a black background and examine them 

 carefully. The ammonium hydroxide, by diffusing into the acid 

 fluid, forms a neutral zone and in this zone will be precipitated any 

 undigested edestan which is present. Select the tube in the series 

 which contains the least amount of gastric juice and which ex- 

 hibits no ring, signifying that the edestan has been completely 

 digested, and calculate the peptic activity of the gastric juice under 

 examination on the basis of the volume of gastric juice used in this 

 particular tube. 



Calculation. Multiply the number of c.c. of edestin solution 

 used by the dilution to which the gastric juice was originally sub- 

 jected and divide the volume of gastric juice necessary to com- 

 pletely digest the edestan by this product. For example, if 2 c.c. 

 of the edestin solution was completely digested by 0.25 c.c. of a 

 I : 20 gastric juice we would have the following expression ; 

 0.25 -f- 20 X 2 or i : 1 60. This peptic activity may be expressed in 

 several ways, e. g., (a) i : 160 pepsin; (b) 160 pepsin content; 

 (c) 1 60 parts. 



3. Quantitative Determination of Tryptic Activity. Gross' 

 Method. This method is based upon the principle that faintly alka- 

 line solutions of casein are precipitated upon the addition of dilute 

 (i per cent) acetic acid whereas its digestion products are not so 

 precipitated. The method follows : Prepare a series of tubes each 



1 This edestin should be prepared in the usual way (see p. 103), and brought 

 info solution in a dilute hydrochloric acid of approximately the same strength 

 as that which occurs normally in the human stomach. This may be conveniently 

 made by adding 30 c.c. of ^ hydrochloric acid to 70 c.c. of water. Ordinarily 

 it should not take longer than one minute to introduce the edestin solution into 

 the entire series of tubes. However, if the edestin is added to the tubes in the 

 same order as the ammonium hydroxide is afterward stratified, no appreciable 

 error is introduced. 



~ Making the stratification in the same order as the edestin solution was added. 



