20 PRINCIPLES OF BIOCHEMISTRY 



investigate. Often, it is true, we can successfully employ destructive, 

 dynamic methods to find out many important things. For example, 

 in the study of digestion, we can destroy the living cells which form the 

 lining mucous membrane of the stomach, and, having destroyed them, 

 extract from them a substance, Pepsin, which will digest proteins, even 

 in glass vessels in laboratory-incubators. In this way and by similar 

 methods we can study the changes which are brought about in our 

 foodstuffs when they enter the alimentary canal. Even in a fairly 

 simple case such as this, however, the dynamic method does not 

 altogether suffice. For we find that within the alimentary canal itself 

 the foods are digested much more rapidly than we can digest them with 

 the aid of ferments in laboratory-glassware. Some condition, other 

 than mere warmth or mechanical agitation, some condition which we 

 have not yet fully succeeded in imitating, very materially aids the 

 action of these ferments in the cavity of the living alimentary 

 canal. 



By such phenomena as these we are constantly being reminded that 

 it is not by any means safe to argue directly from the behavior of dead 

 fragments or products of living tissue, to that of living tissue itself. 

 The results of dynamic experiments which involve the actual destruction 

 of the living tissues which we are investigating, only afford a starting- 

 point, therefore, or an orientation, for our guidance in a repetition of the 

 experiment under actual living-conditions. 



Biochemistry, therefore, falls very naturally into two fields of study, 

 differentiated by the methods of investigation employed. The one 

 field, that which has until recently been the peculiar interest of the 

 "physiological chemists," consists in the study of the crude substances 

 which enter into the life-flame and the products which leave it. The 

 foodstuffs and the excreta, and, incidentally, the composition of dead 

 matter that once was living, also the study of the action and reaction 

 of fragments of living or dead protoplasm upon the foods or upon one 

 another, these, until comparatively recently, comprised the whole 

 activity and interest of chemistry in the investigation of living matter. 

 It is obvious, however, that while knowledge of these things is an 

 essential prerequisite to the understanding of the chemical phenomena 

 of life, yet they are far from yielding information as to the nature of 

 life-processes themselves. It was for this reason, and with justice, 

 that one of the greatest contributors to our knowledge in this field, 

 G. von Bunge, exclaimed in 1894, "All processes in the organism which 

 may be explained mechanically are no more phenomena of life than are 

 the movements of the leaves and branches of a tree that is shaken by 

 the storm, or the movement of the pollen that the wind wafts from the 

 male poplar to the female." 1 We were at that time hovering upon the 

 outskirts of the main problems, since actual penetration of them was 

 necessarily deferred until the momentous advances of physical chemis- 



1 Lchrbuch der Physiologischen und Pathologischou Chcraio, 3tc Aufl., Leipzig, 1894. 



