164 C. M. CHILD. 



Moreover, the phenomena of all differential acclimation and 

 recovery in growth and development indicate very clearly that 

 the metabolic activity of protoplasm is a factor in susceptibility. 

 With the advance of our knowledge it becomes increasingly evi- 

 dent that the factors concerned in the permeability of living pro- 

 toplasm are essentially those concerned in other aspects of life 

 and that permeability is an expression of the physiological state 

 of the plasma membranes. If we admit this, differences in per- 

 meability are themselves to some extent indicators of differences 

 in physiological state, but it still remains true that susceptibility 

 is not simply a matter of the rate of penetration of the plasma 

 membranes but rather of the rate of killing or alteration of the 

 membranes and superficial regions of protoplasm by an external 

 agent. Different external agents may and undoubtedly do act 

 chiefly or primarily upon different factors concerned in the main- 

 tenance of physiological state, but since these different factors 

 are mutually associated in such maintenance, the general result 

 as regards susceptibility, i.e., the general effect on the physio- 

 logical state, may be and is the same for at least many different 

 agents. In short, susceptibility is within certain limits and in a 

 general way an index of physiological state in protoplasm and 

 the axial gradients in susceptibility are therefore significant, par- 

 ticularly when their existence is confirmed by other methods, as 

 indicating the existence of non-specific or quantitative differences 

 as the earliest distinguishable features of axiation. 



Demonstration of the Gradients by Reduction of KMnO and 

 by the Indophenol Reaction. The axial gradients have also been 

 demonstrated in many forms as a differential in the rate and 

 amount of reduction of potassium permanganate by protoplasm. 

 It is a well known fact that KMnO 4 is reduced by protoplasm 

 and the reduced salt appears on or in the protoplasm as a brown 

 or blackish precipitate. All axiate forms examined including 

 numerous protozoa, eggs, embryonic and larval stages or adults 

 of the lower invertebrates, echinoderms and smaller arthropods 

 and various algae among plants show gradients in the rate of 

 staining by permanganate corresponding to the gradients demon- 

 strated by susceptibility and other methods. The precipitation of 

 the reduced salt and the appearance of the brown color appar- 



