APPENDIXES 741 



These conclusions do not exclude the possibility that the gradient pattern, either 

 from the beginning of development or from a later stage, involves specifically different 

 substances differently distributed, as Runnstrom and his co-workers maintain; but 

 even if this is the case, differential susceptibility, which is not regionally specific with 

 different agents, and differential dye reduction may be expected to indicate similar 

 gradient directions, as they do very generally. 



