AXIAL SUSCEPTIBILITY GRADIENTS. 395 



chemically active protoplasm of cyanides and other agents used. 

 This, however, is not the case. There is no reason for believing 

 that different agents which retard or inhibit metabolic activity 

 in living protoplasm all act in the same way. Protoplasm is a 

 complex system in which both the physical substratum and the 

 chemical reactions play a part, but the important point is that 

 it is a system, i. e., that the different processes, changes and 

 conditions in it are not independent of each other but mutually 

 correlated and dependent to a greater or less degree. It is not 

 in the least improbable that different agents may give the same 

 general results, as regards susceptibility, even though one acts 

 primarily on the aggregate condition of the colloids or let us say 

 the permeability of membranes, another on the production or 

 constitution of enzymes, and still another on the chemical re- 

 actions of oxidation. My observations on susceptibility to 

 cyanides, various narcotics, acids, alkalies, metabolic products, 

 and even temperature have convinced me that the relation 

 between susceptibility to retarding or inhibiting agents and 

 conditions and general metabolic rate or the rate of certain 

 fundamental metabolic reactions is a very general relation and 

 there seems to be absolutely no reason for believing that it is 

 dependent upon any one particular method of action on the 

 protoplasmic system of the agent or condition employed. It still 

 remains of course for future investigation to determine the 

 exact method of action of each agent and condition, to formulate 

 the general rule and to discover and account for exceptions if 

 they exist. Since our present knowledge indicates both that 

 the oxidations are fundamental metabolic reactions and that 

 they are more or less dependent on various conditions in the 

 protoplasmic system; we may expect to find that their rate is 

 altered by a great variety of external agents and conditions 

 even though these do not enter directly into the chemical reac- 

 tions of oxidation. 



In certain cases, as in the green plants, the energy for certain 

 of the synthetic or anabolic reactions is derived directly from 

 sources outside the organism and in such cases these reactions 

 may be to a considerable degree independent of the energy- 

 producing reactions in the organism. Such reactions, however, 



