NUTRITION IN SENESCENCE AND REJUVENESCENCE 175 



physiologically as those kept on other diets. Their susceptibility 

 is distinctly lower than that of animals at the same stage in nature 

 or in stocks kept on a diet of Uver or earthworm. Their motor 

 activity is also less than that of these animals and their rate of 

 growth is slow. There can be no doubt that these animals undergo 

 much less rejuvenescence in the reproductive and reconstitutional 

 processes than do those on the other diets, and it is evident that the 

 degree of rejuvenescence is progressively less in each successive 

 generation. 



These experiments with different diets have been described at 

 some length because they demonstrate that the course of the Ufe 

 cycle may be very greatly altered by the character of nutrition. 

 The effect of the mussel diet is to a certain degree inherited and 

 cumulative from one generation to another and in this respect 

 differs from that of the other diets. The chief value of these 

 experiments lies in their suggestiveness as indicating what 

 may be accompHshed with diets carefully hmited to particular 

 kinds of cells or tissues or to substances of particular chemical 

 constitution. 



REFERENCES 



Child, C. M. 



191 1. "A Study of Senescence and Rejuvenescence Based on Experiments 

 with Planarians," Arch. f. Entwickelungsmech., XXXI. 



1914. "Starvation, Rejuvenescence and Acclimation in Planaria doro- 

 tocephala," Arch. f. Entwickelungsmech., XXXVIII. 



Citron, E. 



1902. "Beitrage zur Kenntnis von Syncoryne sarsii," Arch. f. Naturge- 

 schichte, Jhg. LXVIII. 



DOWNEROWITSCH. 



1892. "On the Changes in the Spinal Cord during Complete Starvation" 

 (Russian), Bolnitschnaja Gaseta Botkina, 1892. 



GUDERNATSCH, J. F. 



1912. "Feeding Experiments on Tadpoles: I, The Influence of Specific 

 Organs Given as Food on Growth and Differentiation," Arch. 

 /. Entwickelungsmech., XXXV. 



1914. "Feeding Experiments on Tadpoles: II, A Further Contribution 

 to the Knowledge of Organs of Internal Secretion," Am. Jour, of 

 Anat., XV. 



