3G J. WILLIAM BUCHANAN 



physical and chemical properties, when considered in the light 

 of the data, preclude the idea of specific effects and force one 

 to conclude that their common effect on head frequency is due 

 to their common property of anesthesia. The data show very 

 clearly that this common property prevents to at least a marked 

 extent the stimulation of the pieces by section. 



But this common effect of the anesthetics in preventing the 

 stimulation of section produces different effects on the head 

 frequency in the A and C pieces. One must therefore look for 

 some sort of difference in the two regions to explain these results. 

 Since morphological and specific differences have been excluded, 

 the difference must be physiological and quantitative. A dif- 

 ference in the rate of metabolism between the A and C regions 

 of intact animals is known to exist. They represent, respec- 

 tively, regions or levels near the apex and base of an anteropos- 

 terior gradient in rate of metabolism. Much evidence has accu- 

 mulated to show that the head frequency of isolated pieces 

 depends in large part on their original position in this gradient. 

 As outlined in the introductory pages of this paper, the X region 

 of pieces is stimulated directly by the injury of cutting and is 

 also isolated from all regions anterior to it. The Y region is 

 also stimulated at the same time, in part at least, by impulses 

 arising from the severing of the nerve tracts. In pieces of a 

 given length, the more posterior the piece, the greater the stimu- 

 lation of the Y region; i.e., B pieces are more stimulated than 

 A pieces and C pieces are more stimulated than B pieces. The 

 stimulation of the Y region in all pieces is temporary. The high 

 rate of the X region brought about by the wound is continued 

 by the processes of dedifferentiation and redifferentiation ini- 

 tiated shortly after section. Before a piece is cut from the 

 body of the animal, the cells near the level of the cut and to be 

 included in the piece, i.e., the X cells, function as integrated 

 units of a complete organism. After section the only remaining 

 integrative control of these cells must emanate from the Y region. 

 The more active and intense these controlling factors, the greater 

 their effect in maintaining the specialization of the cells at X as 

 functional units of the old organism. But if for some reason the 



