GASTRIC ANALYSIS 169 



to the sixth, i.o c.c.; and to the seventh, i.o c.c. of the diluted juice boiled. These 

 measurements can be accurately made with a i c.c. pipette graduated in o.oi c.c. 

 All tubes are then immersed for 15 minutes in a water-bath at 50 to 52C. At the 

 end of this time, the tube is selected which is clear and contains the least amount of 

 diluted gastric juice. Upon this basis, the peptic activity is calculated as the num- 

 ber of cubic centimeters 0^0.25 per cent globulin digested by i c.c. of undiluted 

 gastric juice. For example, if tube 2 containing 0.3 c.c. of a 12.5 times diluted 

 juice be clear, then the result would be expressed: 



Peptic activity =(i -5-0.3) X 12. 5 = 41. 2. 



Ordinarily this scheme of seven tubes is used, though it is not a rule. If the 

 free acidity be high, sometimes a dilution of ^5 is made. The number of tubes 

 used will depend upon the accuracy desired. 



(d) Determination of Tryptic Activity. Trypsin is not a gastric 

 enzyme but occurs in the pancreatic juice (see page 188). In case of 

 regurgitation of intestinal contents through the pylorus trypsin would 

 be passed into the stomach. This regurgitation is doubtless of frequent 

 occurrence and may even be a normal mechanism by which gastric 

 acidity is regulated (see page 151). Trypsin is, therefore, generally 

 present in the contents of the normal human stomach. 



Spencer's Method. 1 (a) Prepare five reagent tubes, Nos. i, 2, 3, 4, and 5; more 

 if desired. 



To tubes i and 2 add 0.5 c.c. of gastric contents (filter if cloudy). 



(b) To tubes 2, 3, 4, and 5 add 0.5 c.c. of distilled water. 



(c) From tube 2 remove 0.5 c.c. of its mixed contents and add to tube 3. Mix 

 thoroughly and add 0.5 c.c. from tube 3 to tube 4. Repeat for tube 5. 



We now have dilutions of gastric contents of i, ^, ^, 3^, and 3^6- 



(d) To each tube add one drop of phenolphthalein solution (phenolphthalein 

 i gram; alcohol (95 per cent) 100 c.c.); then add drop by drop a 2 per cent sodium 

 bicarbonate solution until a light pink color is produced. 



(e) To tubes i, 2, 3, and 4 add 0.5 c.c. of casein solution. Tube 5 must receive 

 i c.c. of casein solution, since it contains i c.c. of the diluted gastric contents. For 

 the casein solution, dissolve 0.4 gram of casein in 40 c.c. of N/io NaOH. Add 130 

 c.c. of distilled water, then 30 c.c. of N/io HC1. This leaves the solution alkaline 

 to the extent of 10 c.c. of N/io NaOH, minus about 3 c.c. neutralized by the 

 casein. 



(/) Incubate for five hours at 4oC. 



(g) Precipitate the undigested casein by dropwise addition of a solution of the 

 following composition: glacial acetic acid i c.c., alcohol (95 per cent) 50 c.c., dis- 

 tilled water 50 c.c. The tubes in which digestion has been complete remain clear; 

 others become turbid. 



(ti) The tryptic values are expressed in terms of dilution. Thus, complete 

 digestion in tube 3 (a dilution of y) shows four times the tryptic power of un- 

 diluted gastric juice; taken as a standard as i, therefore, its tryptic value is 4. 



Elaborated by Dr. W. H. Spencer (Jour. Biol. Chem., 21, 165, 1915) in the author's 

 laboratory for the specific purpose of determining trypsin in gastric juice. For other tryp- 

 sin methods see Chapter X. 



