CO 2 IN RELATION TO REGENERATION IN PLANARIA. IIQ 



pieces. In other words, the new individuals developed from 

 pieces show a susceptibility to lack of oxygen equal to or greater 

 than that of much smaller younger animals than those from 

 which the pieces were taken. These observations concern 

 primarily the susceptibility of ectoderm and body wall. 



CONCLUSION. 



These experiments constitute a new test of the validity of the 

 susceptibility method as a rough comparative means of deter- 

 mining physiological or metabolic condition and at every point 

 the differences and changes in susceptibility, as determined by 

 KNC and in many cases by various other agents also, are paral- 

 leled by differences and changes in rate of CC>2 production. 

 Even the temporary stimulation of the pieces after section, which 

 is slight or absent in the A -pieces and very marked in the C-pieces, 

 appears in the data on CO 2 production and the increase in rate, 

 at least of respiratory metabolism associated with regulation, is 

 evident in the marked increase in rate of CO 2 production even in 

 the "old" parts of the regenerated animal. This work may per- 

 haps be regarded as in some respects the most delicate test of the 

 relation between susceptibility and respiration which has been 

 made up to the present. 



As has been repeatedly stated, the susceptibility method is 

 not an exact quantitative method, but a rather crude means of 

 indicating differences of some sort in physiological condition 

 and the differential susceptibility of different regions of the 

 same individual affords a means of modifying and controlling 

 various developmental and other processes. The facts at hand 

 concerning susceptibility, e.g., the lack of specificity, the close 

 relation between susceptibility and physiological activity in 

 development, growth and function as well as the positive evidence 

 already obtained concerning the parallelism between suscepti- 

 bility, oxygen consumption and CO 2 production indicate very 

 clearly that a more or less definite relation exists between the 

 susceptibility of living protoplasm, to at least many external 

 agents and conditions within certain ranges of concentration or 

 intensity, and the rate or intensity of certain fundamental 

 physiological processes, particularly those which liberate energy. 



