SUSCEPTIBILITY GRADIENTS. 83 



hair gradient is basipetal but the cell gradient is very generally 

 acropetal. 



Evidently the acropetal cell-gradient observed in 1915 is not a 

 natural condition but represents a reversal of the cell gradient 

 by neutral red or by other conditions, and this appears as a 

 reversed susceptibility gradient to KCN or HgCl 2 . These hairs 

 take up neutral red rapidly and stain very deeply, and the axial 

 differences in susceptibility to neutral red within the elongated 



FIG. 4. 



cell are sufficient to bring about reversal of the susceptibility 

 gradient after a time. If death occurs early the reversal does 

 not appear, but if the concentration of neutral red is low enough 

 to allow survival for two or three hours in the solution, reversals 

 of the cell gradient begin to appear. 



Further observations showed that after two or three days in 

 the laboratory the intracellular gradient was frequently reversed, 



