PEPSIN DIGESTION. 471 



tory. 1 Sulphuric acid, it seems, has a weaker action than the other 

 inorganic acids. The degree of acidity is also of the greatest importance. 

 With hydrochloric acid the degree of acidity is not the same for differ- 

 ent protein bodies. For fibrin it is 0.8-1 p. m., for myosin, casein, and 

 vegetable proteins about 1 p. m., for coagulated egg albumin, on the 

 contrary, about 2.5 p. m. In regard to the dependence of the extent 

 of transformation upon the quantity of enzyme and the time of diges- 

 tion we refer to page 58. The kind of protein is of importance, for 

 example, for besides what was said above in regard to the fibrin, hard- 

 boiled egg albumin is much easier digested by an acidity of 1-2 p. m. 

 HC1 than liquid egg albumin, which is rather resistant to the action 

 of gastric juice. The accumulation of products of digestion has a retard- 

 ing action on digestion (page 65), although, according to CHITTENDEN 

 and AMERMAN, 2 the removal of the digestion products by means of dialysis 

 does not essentially change the relation between the proteoses and true 

 peptones. Pepsin acts more slowly at low temperatures than it does at 

 higher ones. It is even active in the neighborhood of C., but with 

 increasing temperature the rapidity of digestion also increases until 

 about 40 C., when the maximum is reached. If the swelling up of the 

 protein is prevented, as by the addition of neutral salts, such as NaCl, 

 in sufficient amounts, or by the addition of bile to the acid liquid, 

 digestion can be prevented to a greater or less extent. Foreign bodies 

 of different kinds produce dissimilar effects, in which naturally the 

 variable quantities in which they are added are of the greatest impor- 

 tance. Salicylic acid and carbolic acid, and especially sulphates 

 (PFLEIDERER), retard digestion, while arsenious acid promotes it (CHIT- 

 TENDEN), and hydrocyanic acid is relatively indifferent. Salts of the 

 alkali and alkaline earth metals have a strong retarding action in strong 

 concentration. By experiments with salt solutions so strongly diluted 

 that the action, on account of the strong dissociation, was brought about 

 by ions and not by the electrolytically neutral molecules (min. ^ and 

 max. J normal salt solutions), J. ScnuTz 3 found that the anions had a 

 much greater retarding action upon pepsin digestion than the cations. 

 Of these latter the sodium cation had the strongest retarding action. 

 Alcohol in large quantities (10 per cent and above) disturbs the digestion, 

 while small quantities act indifferently. Metallic salts in very small 

 quantities may indeed sometimes accelerate digestion, but otherwise 



1 See Wr6blewski, Zeitschr. f. physiol. Chem., 21, and especially Pfleiderer, Pfliiger's 

 Arch., 66, which also gives references to other works; Larin, Biochem. Centralbl., 1, 

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



2 Journ. of Physiol. 14. 



1 Hofmeister's Beitrage, 5. 



