NUTRITION IN SENESCENCE AND REJUVENESCENCE 163 



the third about 50 per cent. Similarly, in the much smaller worms 

 of Table IV the average decrease in length during the first month 

 is 30 per cent, and during the second, 50 per cent. In these cases 

 the measurements for each month were made on different lots of 

 worms from the same stock. Doubtless a continuous series of 

 measurements of the same individuals would bring out the differ- 

 ences in rate of decrease still more clearly. When the animals are 

 not kept entirely without food the rate of reduction does not in- 

 crease, but may even decrease in later stages, for the smaller the 

 animals, the more completely does a small amount of food retard 

 or inhibit reduction. This increase in rate of reduction during 

 starvation confirms the observations on susceptibility and on 

 carbon-dioxide production, for it indicates that the rate of meta- 

 bolic processes increases as reduction proceeds. 



In this connection the study by Mayer ('14) of loss of weight 

 in a jelly-fish, Cassiopea, is of interest. From his data Mayer con- 

 cludes that the relative loss of weight for each day or other period 

 is in general the same throughout the course of starvation. More- 

 over, the nitrogen-content and water-content of the body do not 

 show any change in relation to starvation. At first glance it 

 appears that the course of starvation in this medusa differs from 

 that in Planaria. While the metabolic condition of the animals 

 during starvation has not been determined, the constancy in the 

 percentage of loss of weight indicates that the metabolic rate does 

 not increase as starvation and reduction proceed. As a matter of 

 fact, however, Mayer's data, and particularly the curves of loss 

 of weight, show that in most cases the loss of weight in uninjured 

 animals during the first two or three weeks of starvation is slightly 

 less than the calculated loss according to the formula which Mayer 

 has adopted, while during the later period of starvation the observed 

 loss of weight equals or in many cases exceeds the calculated loss. 

 In mutilated animals, which are undergoing regeneration as well 

 as starvation, the observed loss of weight during the earlier stages 

 of starvation is in most cases more rapid than the calculated loss, 

 but the two coincide more nearly in later stages. 



It is probable then that Mayer's lawof loss of weight is only an 

 approximation based on averages, and that some slight increase 



