446 DIGESTION. 



ing influence upon pepsin digestion, is to be tested, then the liquid must be first 

 properly diluted with 2-4 p. m. hydrochloric acid (NIERENSTEIN and SCHIFF *). 



Objections have been raised against these methods from several sides, espe- 

 cially by GRUNTZNER, but they can be recommended for practical purposes as 

 being simple and rather accurate. HUPPERT and E. SCHUTZ measure the relative 

 quantities of pepsin from the amount of secondary proteoses formed under cer- 

 tain conditions. The proteoses were determined by the polariscope. J. SCHUTZ 

 determines the total proteose-nitrogen, and SPRIGGS 2 finds that the change in 

 the viscosity is a measure of the amount of pepsin. 



VOLHARD and LOHLEIN 3 use an acid casein solution for the pepsin determina- 

 tion, and determine, after precipitation with sodium sulphate, the acidity of the 

 filtrate of the digested test as well as of the original control solution. The casein 

 is precipitated as an acid compound by the sulphate, and the filtrate separated 

 from the precipitate contains less acid than the original solution. In propor- 

 tion as the digestion progresses less substance is precipitated by the sulphate, 

 and the acidity of the filtrate becomes correspondingly higher. The increase 

 in acidity in the different portions varies within certain limits as the square root 

 of the quantity of ferment. 



JACQBY suggested a method which is based on the fact that a cloudy solution 

 of ricin becomes clear by the action of pepsin-hydrochloric acid, and indeed with 

 varying rapidity with different quantities of pepsin. This method, which requires 

 further testing, seems to be delicate and is of value, as is doubtless the following 

 method of FULD and LEVISON.* This is based on the property that edestan can 

 be precipitated from acid solution by NaCl, but not the proteoses formed therefrom : 



A solution of 1 p. m. edestin in hydrochloric acid (TO normal) is prepared 

 whereby the edestin is changed into edestan. The activity of a gastric juice (or 

 a pepsin-hydrochloric acid solution) is tested in the following manner: the solu- 

 tion to be tested is placed in decreasing quantities in a series of test-tubes and 

 allowed to act upon an equal quantity of the edestan solution, 2 cc., and the 

 minimum of juice determined which is necessary to digest the solution, within 

 one-half an hour and at room temperature, so that on the addition of solid 

 NaCl and shaking no precipitate occurs. GROSS 5 suggested a similar method by 

 using an acid casein solution and precipitating with sodium acetate. 



The rapidity of the pepsin digestion depends on several circumstances. 

 Thus different acids are unequal in their action ; hydrochloric acid shows 

 in slight concentration, 0.8-1.8 p. m., a more powerful action than any 

 other acid, whether inorganic or organic. In greater concentration other 

 acids may have a powerful action; but no constant relation has been 

 found between the strength of various acids and their action in pepsin 

 digestion, and the reports of the action of different acids are contradic- 

 tory. 6 Sulphuric acid, it seems, has a weaker action than the other 



1 Mett, see Pawlow, I.e., 31; Nierenstein and Schiff, Berl. klin. Wochenschr., 40; 

 Jastrowitz, Bioch. Zeitschr., 2. 



2 Huppert and Schiitz, Pfliiger's Arch., 80; J. Schiitz, Zeitschr. f. physiol. Chem., 

 30; Spriggs, ibid., 35. 



3 Hofmeister's Beitrage, 7. 



4 Jacoby, Bioch. Zeitschr., 1; Fuld and Levison, ibid., 6. 



5 Berl. klin. Wochenschr., 45. 



6 See Wroblewski, Zeitschr. f. physiol. Chem., 21, and especially Pfleiderer, Pfliiger's 

 Arch., 66, which also gives references to other works; Larin, Biochem. Centrabl., 

 1, 484; and A. Pick, Wien. Sitzungsber., M. N. Klasse, 112. 



