1 68 PHYSIOLOGICAL CHEMISTRY 



sodium chloride solution, warming slightly if necessary. 1 Filter and introduce i c.c. 

 of the clear nitrate into each of a series of six 2 test-tubes about i cm. in diameter. 

 Introduce into each tube i c.c. of 0.6 per cent hydrochloric acid and permit a period 

 of about five minutes to elapse for the development of the turbidity. Make a 

 known volume of the gastric juice (5-10 c.c. is sufficient) exactly neutral to litmus 

 paper with dilute alkali; and record the volume of the alkali so used. If acid 

 metaprotein precipitates, filter it off; if there is no precipitate proceed without 

 nitration. Dilute the clear neutral solution with a known quantity of distilled 

 water (usually 5 volumes) making proper allowance for the volume of alkali used in 

 the neutralization. Boil 5-10 c.c. of the diluted juice, filter and add the following 

 decreasing volumes (c.c.) to the series of six tubes: i.o, 0.9, 0.7, 0.5, 0.2, o.o. Make 

 the measurements by means of a i c.c. pipette graduated in o.oi c.c. Now rapidly 

 introduce the unboiled, diluted juice in the following increasing volumes (c.c.) in 

 order: o.o, o.i, 0.3, 0.5, 0.8, i.o. Each tube now contains a total volume of 3 c.c. 

 and a total acidity of 0.2 per cent hydrochloric acid. Shake each tube thoroughly 

 and place them at 50-5 2C. for 15 minutes or at 3S-36C. for one hour. Examine 

 the series of tubes at the end of the digestion period and select that tube which 

 contains the smallest quantity of gastric juice and which shows no turbidity. The 

 volume of the juice used in this tube is taken as the basis for the calculation of the 

 peptic activity. 



Calculation. The peptic activity is expressed in terms of i c.c. of the undiluted 

 juice. For example, if it requires 0.5 c.c. of the diluted juice (five-fold dilution) to 

 clear up the turbidity in i c.c. of the globulin solution in the proper experimental 

 time interval (15 minutes or one hour according to temperature) the peptic activity 

 would be expressed as follows: 



(i-7-o.5)X5 = io (peptic activity). 



According to this scale of pepsin units 10 may be considered as "normal" peptic 

 activity. These units are about ^fo as large as those expressed by the Jacoby- 

 Solms scale. 



Inasmuch as it has been shown 3 that blood serum contains an antipepsin it is 

 advisable to test the gastric juice for blood before determining its proteolytic power. 



(4) Given's Modification of Rose's Method. 4 The gastric contents are 

 strained through cheese cloth. Two c.c. are measured by means of an Ostwald pipette 

 into a 25 c.c. stoppered volumetric cylinder, and diluted to the mark with dis- 

 tilled water. Into each of seven small test-tubes (i X 10 cm.) is measured, with 

 an Ostwald pipette, i c.c. of a 0.25 per cent filtered pea globulin in 10 per cent 

 sodium chloride solution. To each tube is added i c.c. of 0.6 per cent hydro- 

 chloric acid, also by means of an Ostwald pipette. The tubes are allowed 

 to stand about five minutes, until the maximum turbidity develops. To the 

 first five, distilled water is added as follows: To the first, 0.9 c.c.; to the second, 

 0.8 c.c.; to the third, 0.7 c.c.; to the fourth, 0.6 c.c.; and to the fifth, 0.2 c.c.; to 

 the sixth and seventh, none. Then there are rapidly added to each test-tube 

 the following amounts of the diluted (i : 12.5) gastric juice; to the first, o.i c.c.; to 

 the second, 0.2 c.c.; to the third, 0.3 c.c.; to the fourth, 0.5 c.c.; to the fifth, 0.8 c.c.; 



1 This solution may be preserved at least two months under toluene. 



2 A longer series of tubes may be used if desired. However, experience has shown that 

 a series of six ordinarily affords sufficient range for all diagnostic purposes. 



3 Oguro: Biochemische Zeitschrift, 22, 266, 1909. 



4 Givens: Hygienic Lab. Bull. 101, p. 71, August, 1915. 



