THE AXIAL GRADIENTS IN HYDROZOA. 95 



manganate shall penetrate to the interior of the cell before the 

 reaction begins. Moreover, the protoplasm in which the reaction 

 occurs is undoubtedly killed very rapidly, as is indicated by the 

 almost instantaneous cessation of ciliary and flagellar activity, 

 even in very low concentrations of permanganate. It is certain 

 that the permanganate does not penetrate the plasma membrane 

 or any other limiting surface to any appreciable extent while 

 that surface is living, but rather kills or begins killing as it comes 

 into contact with the surfaces. My observations indicate, how- 

 ever, that the differences in rate of reduction disappear after 

 death. If this is true, permeability in any physiological sense, 

 i.e., permeability of living protoplasmic limiting surfaces, cannot 

 be the chief factor in determining the gradients in rate of reduc- 

 tion, for any differences in such permeability must disappear very 

 soon on contact with the solution. If the particular limiting 

 surfaces persist as limiting surfaces after the action of perman- 

 ganate, and it is by no means certain to what extent they do 

 persist, their permeability is no longer the physiological perme- 

 ability of the living surface, but simply that of a dead surface. 

 In short, after a given limiting surface, whether external or 

 internal, has been killed by permanganate, the further passage 

 of that surface by permanganate is not determined by its physio- 

 logical permeability. If this argument is correct, the differences 

 in rate of reduction of permanganate determined by differences 

 in physiological permeability should be slight, since permanganate 

 is highly toxic, but, as a matter of fact, the differences are very 

 great when living animals are brought into the solutions and 

 absent, or almost absent when dead animals are used. 



Moreover, the deposition of MnOo or other oxides in the proto- 

 plasm is the result of a chemical reaction between the permanga- 

 nate and protoplasmic constituents and therefore depends on 

 other factors than the mere entrance of the agent. There is 

 every reason to believe that the chemical and particularly the 

 oxidative activity of the protoplasm is a factor in determining 

 the velocity of the reaction, even though death occurs rapidly. 

 Exactly what changes constitute death in permanganate, or for 

 that matter in any other agent, it is impossible to say, but it is 



