ACTION OF THE ENZYMES. 117 



figures from 1 to 6, according to the amount of color pro- 

 duced. In each digestion -tube were present the same amounts 

 of fibrin and pepsin and chemically equivalent amounts 

 of the various acids. 



At a. somewhat higher concentration (for example, 1/20 

 normal) both the acetic and sulphuric acid tubes would 

 have shown some degree of fibrin digestion, but the order 

 of the table would not have been much different. With- 

 out further comment, therefore, it is clear that while the 

 effect of any acid upon the proteolytic activity of acid- 

 proteinase is chiefly a function of the number of hydrogen 

 ions which the acid yields on solution in water, the indi- 

 vidual acids vary enough from each other even when the 

 number of hydrogen ions in the unit volume of the digestion 

 mixture is the same to make us inquire after the cause of 

 this difference. Sulphuric acid, for example, which in 

 dilute solution is dissociated to about the same degree as 

 hydrochloric, stands far below this in its power of bringing 

 about a demolition of the protein molecule. Now since 

 sulphates in general (sodium sulphate, magnesium sul- 

 phate, etc.) markedly retard the activity of acid-proteinase 

 even when this is acting in the presence of hydrochloric 

 acid, it lies near at hand to consider the S04 constituent 

 of the sulphuric acid and of these salts as chiefly respon- 

 sible. Other salts, such as the chlorides and iodides of 

 sodium, potassium, and ammonium, also inhibit the diges- 

 tion of a protein under the influence of acid proteinase and 

 hydrochloric acid, but not so markedly as the sulphates. 



The reason for the individual differences between the 

 acids and the effect of various salts upon the velocity of 

 digestion is not yet entirely clear. It is evident that the 

 nature of their action might be various. In looking over 

 PFLEIDERER'S tables, however, one is struck with the parallel- 

 ism which exists everywhere between the effect of the different 

 acids and the various salts upon the rate of digestion and 

 the degree of swelling which these substances bring about 



