134 c - M - CHILD. 



themselves constitute only one aspect of such a gradient: asso- 

 ciated with them are unquestionable differences in dispersion of 

 colloids, permeability of membranes, enzyme content or ac- 

 tivity, electrolytic dissociation and ion content, electrical poten- 

 tial, etc., and the point of view determines, at least to a consider- 

 able degree, which factor or group of factors in the complex we 

 regard as fundamental. The essential fact is that these gradients 

 in protoplasmic condition and activity exist and that they are 

 not only characteristic features of physiological axes, but repre- 

 sent the earliest and simplest condition of such axes that we have 

 thus far been able to discover. 



The results given by the susceptibility method have been 

 extended and confirmed by various other experimental methods 

 and are not only in complete agreement with, but afford a satis- 

 factory interpretation of a wide range of facts of observation 

 and experiment, such, for example, as axial gradients in protoplas- 

 mic structure, in accumulation of yolk and other reserves, in 

 rate of growth and ability to grow at the expense of other parts, 

 in irritability and various other physiological activities. 



During the past summer I have made extensive use of potas- 

 sium permanganate as an agent for demonstrating the physio- 

 logical gradients in protoplasm and making them directly visible 

 as color gradients. Most of this work was done at the Puget 

 Sound Biological Station at Friday Harbor, Wash., and I am 

 indebted to the director, Dr. T. C. Frye and to the University 

 of Washington for the privileges afforded me. 



THE METHOD. 



In consequence of its powerful oxidizing action and the stain 

 resulting from its reduction, potassium permanganate has long 

 been used to some extent in histology, and certain investigators 

 have attempted to determine with this and various other reagents 

 the loci of reduction and of oxidation or of low and high oxygen 

 content in cells and tissues. (See for example Golodetz and 

 Unna, '09, P. G. Unna, 'n, '13, '15, and various other papers.) 

 The methods and results of these authors have been criticized 

 (Oelze, '140, b, c, Schmidt, '12, Schneider, '14) and their validity 

 defended (Golodetz, '14, Unna, '15), but this controversy does 



