750 



itself especially in strong acid solutions and is instrumental in shifting 

 the optimum of digestion in pepsin-containing solutions towards the 

 stronger acid solutions. 



I have expatiated on this point because the question is rather 

 knotty ; also because I wanted to show (hat we cannot expect to 

 find complete concordance between maximum of swelling and optimum 

 of the action of pepsin. The results of a set of experiments with 

 dialyzed and iiltered horse-serum have been tabulated in Table V. 



TABLE V. 



Estimation of the action of pepsin upon dialyzed and filtered horse- 

 serum in 4 hrs. at 37^; estimation of the viscosity in these solutions 

 with inactive pepsin at 18°. 



The pepsin-solution contained 50 mgr. of pepsin tal<en up in 50 c.c. 

 very dilute oxalic acid solution, 5 c.c. was used for every protein-solution. 

 The estimation of the viscosity was made 5 min. after the mixing of 

 the protein and the acid; for these tests the pepsin had been inactivated. 

 The estimations were made at 18°, since at 37° it was quite impossible 

 to obtain at all values representing the initial condition. Of course the 

 viscosimeter, the liquids, the pipettes etc. were heated up beforehand 

 to 18', so that after the mixing we had not to wait longer than five 

 minutes. 



When representing the viscosity graphically as a function of 

 pu, the maximum appears to lie at pa =2.5. The optimum of the 

 peptic action lies at pH = 1.7. Sorensen's values of the latter are 

 from 1.6 — 2.26 according to the duration of the digestion. In the 

 light of these very reliable values and the above mentioned causes 

 of tiie varying maxima of viscosity and swelling I am induced to 



