THE AXIAL GRADIENTS IX HYDROZOA. 29 



THE PHYSIOLOGICAL SIGNIFICANCE OF THE VARIOUS METHODS. 

 The first question which arises is whether the axial differences 

 in susceptibility to the various agents used result merely from dif- 

 ferences in permeability of the limiting surfaces of the cells. 

 That axial differences in permeability to some, if not to all agents, 

 corresponding more or less closely to the gradients observed, do 

 exist is probable. But that such differences are not the only, nor 

 the fundamental factors in the gradients is indicated by various 

 facts, some of which require brief consideration in connection 

 with the case in hand. First, an observation made repeatedly on 

 of both Phialidium and Stomotoca teased from the gonad 

 is at 1- stive in this connection. As already noted, the 



: during the growth period and when they are 

 teased out of the gonad rupture of the cytoplasm occurs at the 

 attached pole and, although the injured region closes within an 

 hour or two. the intact plasma membrane present over other parts 

 of the sin absent in this region for some time and granules 



re often given off into the water. But even while 

 tlii- la -mil- region is exposed, it does not become the high 



end ft" thi ility gradient or the reduction gradient. That 



is at the opposite pole, in spite of the fact that the agents must 

 per the intact membrane there in order to produce their 



ly effect of the exposure of the cytoplasm at the 

 attached ; a little superficial cytolysis or reduction. This 



al)M :inn between the polar gradient of the oocyte 



and the injury at the attached pole is striking. 



Mrds the action of the various agents used to 

 den te the gradients by cytolysis, it is important to note 



that the cytolytic gradients are the same for agents such as methy- 

 lene blue and neutral red which penetrate living membranes 

 readily and kill by accumulation within the cells and for those 

 such as ITgO which, in the concentrations used, alter and kill 

 the cell surfaces rapidly and so destroy such differences in perme- 

 ability as may have existed. Again, the cyanides or the CN 

 ion apparently penetrate cells readily and produce their effects 

 largely within the cells, according to recent views by inhibition 

 of the catalyst of oxidation. As a matter of fact, susceptibility 

 to KCN has been shown in various ways to be, within certain 



