4 J. WILLIAM BUCHANAN 



of the metabolic processes, particularly the oxidative, in differ- 

 ent regions of the animal, has received ample proof. This proof 

 is afforded indirectly by subsequent work showing that the prog- 

 ress of death due to lack of oxygen follows in general the same 

 course as in KNC (Child, '19 b) ; furthermore, as far as the work 

 has been carried out, the rate of carbon-dioxide production 

 measured both by indicator and the Tashiro methods furnishes 

 direct proof that confirms the conclusions drawn from the sus- 

 ceptibility data (Child, '11 b, '15; Tashiro, '17). And last, 

 but perhaps more important, Doctor Hyman has shown that 

 the relative rate of oxygen consumption of different regions 

 agrees in every case with the susceptibility data (Hyman, '21 b). 

 The value of the susceptibility methods as an indicator of meta- 

 bolic conditions has thus been sustained both by direct and in- 

 direct proof. To recapitulate, the existence of an anteroposterior 

 gradient in rate of metabolic processes, particularly those in- 

 volved in oxidative reactions, in Planaria dorotocephala may be 

 considered to have been adequately demonstrated. This gradient 

 is known to involve the following physiological processes: the 

 rate of oxygen consumption, the rate of carbon-dioxide produc- 

 tion, the rate of death in several types of poisons, and the rate 

 of death due to lack of oxygen. The nature of this gradient 

 and its existence in other forms and role in morphogenesis in 

 general have been discussed in a number of papers by Child, 

 Hyman, Bellamy, and others. A general review of the evidence 

 for the existence of such gradients in axiate organisms and their 

 relation to the problem of pattern is given in a recent paper 

 (Child, '20 b). 



The isolation of a piece by section introduces certain quanti- 

 tative changes in the metabolic processes of the isolated part, 

 which are to a greater or less extent dependent on its former 

 level in the gradient. The first change to be considered and 

 probably the first in chronological order is the stimulation pro- 

 duced in immediately adjacent cells by the injury of cutting. 

 The stimulation of injury is a very general phenomenon and 

 requires little discussion here. Tashiro ('17) considers its occur- 

 rence to be suffi.cient evidence that a part is alive. In pieces 



