PHYSIOLOGICAL BASIS OF PATTERN 43 



invertebrates, echinoderms and smaller arthropods and 

 various algae among plants, show gradients in the rate 

 of staining by permanganate corresponding to the 

 gradients demonstrated by susceptibility and other 

 methods. The precipitation of the reduced salt and 

 the appearance of the brown color apparently begin on 

 the external surface of the protoplasm, often within a 

 few seconds after the organisms are brought into the 

 solution, and the differences in rate of precipitation and 

 staining at different levels of an axis are usually very 

 marked. Penetration into the protoplasm usually 

 occurs rather slowly, its rate depending somewhat on 

 concentration, and it is certainly not to any large extent 

 dependent on permeability of living membranes but rather 

 on the killing of the protoplasm from the surface inward. 

 If the reaction is allowed to continue to completion 

 in excess of permanganate, the whole organism may 

 become opaque black and no gradient is visible, but 

 many small organisms thus stained, e.g., blastulae, 

 hydroid planulae, small monosiphonous algae, can be 

 made more or less transparent after such staining by 

 hardening, clearing, and mounting, and in such cases the 

 gradient in staining appears. Under these conditions 

 the gradient represents a gradient in the total amount 

 of reduction of permanganate of which the protoplasm 

 is capable, and it is highly significant to find that the 

 protoplasm of the apical region of a blastula or an alga 

 axis, for example, is capable of reducing more perman- 

 ganate than 'more basal levels. If the organism is first 

 killed by some other agent, e.g., various histological 

 fixing agents, heat, etc., reduction and staining are 

 uniform, or in some cases slight traces of the gradients 



