i6o 



SENESCENCE AND REJUVENESCENCE 



hundred individuals of Planaria dorotocephala in various stages of 

 starvation, and in all cases the susceptibility has been found to 

 increase during starvation. In P. velata also the susceptibility to 

 cyanide has been found to increase during starvation. This 

 species does not undergo reduction in size as rapidly as P. doroto- 

 cephala, but the effect of starvation is essentially the same in both. 

 If the susceptibility of these animals is in any degree a measure of 



lO 



II 



Hours I :; 3 4 5 6 7 ^ 9 



Fig. 57.— Susceptibility of Planaria dorotocephala to KCN o.ooi mol. in relation 

 to nutritive condition and age: ah, dashes, well-fed, growing animals; ab, unbroken 

 line, animals reduced by starvation from 20-24 mm. to 7-8 mm.; cd, animals from the 

 same stock and of the same size at the beginning of the experiment as the star\'ed 

 animals, but which have been fed while other? were starving. 



physiological age, the starving animals certainly undergo rejuvenes- 

 cence, the degree of rejuvenescence varying with the degree of 

 starvation and reduction. 



THE PRODUCTION OF CARBON DIOXIDE BY STARVED ANIMALS 



The invention of the Tashiro biometer (Tashiro, '13) has made 

 possible a direct estimation and comparison of carbon-dioxide 



