DEMONSTRATION OF AXIAL GRADIENTS. 145 



manent, localized and graded differences in permeability in 

 such definite relation to the physiological axes, must be more 

 or less closely associated with differences in metabolic condition, 

 and that in general and within certain physiological limits we 

 may expect to find a higher rate of oxidation associated with 

 a region of higher permeability. Even on this bas's then, the 

 axial gradients in susceptibility, color, etc., would serve as 

 indicators of metabolic gradients. But that a purely physical 

 permeability of chemically inert membranes is not the primary 

 factor in this relation is becoming increasingly evident, not 

 merely in the recent modifications in the conception of per- 

 meability, but in the facts of susceptibility themselves. For 

 example, differences in permeability of different cells or cell 

 regions along an axis to neutral red and certain other "vital" 

 dyes are usually slight and often inappreciable, although in some 

 cases a distinct permeability gradient can be seen. Nevertheless 

 axial gradients in susceptibility to these agents are very distinct, 

 even within the limits of single cells, whether a gradient in pene- 

 tration is distinguishable or not. Certainly physical permea- 

 bility of the cell membrane is not the primary factor in such sus- 

 ceptibility gradients. Again, in the processes of acclimation 

 and recovery that region of an axis which is most susceptible to 

 the agent in high concentration or intensity undergoes acclima- 

 tion most rapidly or completely in low concentrations or inten- 

 sities, or recovers most rapidly and completely after temporary 

 exposure within certain limits. Obviously the axial gradients 

 of acclimation and recovery are very directly dependent upon 

 metabolic rate in protoplasm and purely physical differences in 

 permeability are of minor importance. 



In the light of all the facts, then, I believe we are justified in 

 concluding as regards the color gradients resulting from the pro- 

 toplasmic reduction of permanganate; first, that they are indi- 

 cations of fundamental quantitative differences m the physiologi- 

 cal condition of protoplasm, second, that such condition is very 

 intimately related to the rate of oxidation, third, that the quanti- 

 tative graded differences thus indicated represent the physiologi- 

 cal axis in its simplest form. 



