116 



PHYSIOLOGY OF ALIMENTATION. 



is well known acts upon all proteins thus far studied. Against 

 FRIEDENTHAL and MIYAMOTA can be brought the argument 

 that their preparations were not very active and so may 

 have contained too little of the pure enzyme to give the 

 protein reactions. Further study of the subject is, however, 

 necessary before the question can be looked upon as settled. 

 Acid-proteinase acts only in an acid medium, but the kind 

 of acid is not immaterial. Hydrochloric acid furnishes by 

 far the most favorable medium, but nitric, sulphuric, phos- 

 phoric, lactic, acetic, tartaric, etc., are also active. PFLEI- 

 DERER, 1 \vho has investigated the question physico-chemically, 

 comes to the conclusion that, broadly speaking, different 

 acids favor the action of acid-proteinase on fibrin, according 

 to their "avidity," those with the greater " avidity" acting 

 more powerfully than those with a lesser one. Since we now 

 know that the " avidity" or " strength "' of an acid is an 

 expression of the number of free hydrogen ions it yields 

 upon solution, the above statement may be said to mean 

 that those acids which yield the largest number of hydrogen 

 ions when dissolved in water are most powerful in furthering 

 the activity of acid-proteinase. The following table may 

 serve to illustrate what has been said as well as serve as a 

 text for that which is to follow. The degree' of fibrin diges- 

 i3n as measured by GRUTZNER'S method 2 is expressed in 



1 PFLEIDERER: 



2 See p. 130, 



., 1897, LXVI, p. 605, 



