CO 2 IN RELATION TO REGENERATION IN PLANARIA. 121 



little difference whether or not it shall be found to run exactly 

 parallel to the other indices of total respiration in any particular 

 case. It cannot, however be denied that a wide range of facts 

 determined by many different lines of investigation do indicate 

 clearly the existence of a more or less definite relation between 

 susceptibility and oxidation in at least many cases, and it is of 

 interest to determine range, degree and nature of this relation. 

 The present paper like several others which have recently ap- 

 peared from this laboratory is a contribution to this problem, 

 but it must be remembered that data such as these are not the 

 only criteria of the physiological significance of susceptibility 

 and its relation to the energy-liberating reactions in the metabolic 

 complex. 



SUMMARY. 



1. The colorimetric estimation of CO 2 production shows that 

 the changes in CC>2 production following section in pieces of the 

 body of Planaria dorotocephala run parallel with changes in sus- 

 ceptibility. Immediately following section CO2 production is 

 markedly increased in pieces cut from near the mouth region, 

 while in pieces from regions near the head it is only slightly if at 

 all increased. These changes are temporary excitations fol- 

 lowing section and disappear after a number of hours. 



2. The development of a new individual from a piece is accom- 

 panied by a very considerable increase in COs production which 

 involves not only the new outgrowths at the two ends of the new 

 animal but the "old" parts as well. This increase in CO 2 

 production is found both before and after feeding is resumed 

 following the development of the piece. In these respects also 

 the changes in CC>2 production parallel changes in susceptibility, 

 both series of data indicating that the animal developing from 

 an isolated piece becomes in the course of this development, 

 physiologically younger than the animal from which the piece 

 originated. 



REFERENCES. 

 Allen, G. D. 



"18 Quantitative Studies of the Rate of Respiratory Metabolism in Planaria, 



I. Amer. Jour. Physiol., XLVIII. 



'19 Quantitative Studies, etc., II. Amer. Jour. Physiol., XLIX. 

 Child, C. M. 



'10 Physiological Isolation of Parts and Fission in Planaria. Arch. f. 



Entwickelungsmech., XXX., II. Teil. 



