WEIGHTS OF ORGANS IN UNDERFED YOUNG RATS 105 



percentage of water-content of the body increases, and it is quite 

 probable that during chronic inanition resulting from main- 

 tenance of a young, growing animal at constant body-weight 

 the amount of living protoplasm in the body decreases. If the 

 amount of metabolism is thereby decreased, a smaller food- 

 supply would suffice for maintenance. 



As will be shown later, on account of the intensity of the 

 growth-impulse, especially during the earlier periods of inanition, 

 certain growth-changes occur which require the expenditure of 

 energy. It is possible that this energy is supplied by the excess 

 of food above that required for maintenance proper. Another, 

 but less probable, explanation might be that during inanition 

 the food-intake is in some way more economically utilized, a 

 smaller quantity therefore being sufficient for maintenance. 

 In the later stages of inanition, there is probably a decrease in 

 the temperature of the body, which would therefore require 

 less food. 



Rats held at constant body-weight from the age of three weeks 

 to ten weeks, while becoming more active as the experiment 

 proceeds, become at the same time less resistant to cold. They 

 may die suddenly if the room temperature is lowered, or even 

 without any apparent cause. Thus up to sixteen weeks, the 

 longest successful period in those begmning at three weeks, it 

 becomes increasingly difficult to maintain them alive at con- 

 stant body-weight. WTien the experiment is begun later, the 

 length of the time during which the body-weight can be held 

 constant is considerably increased. Aron ('11) had a similar 

 experience with dogs, finding it necessary after a time to feed 

 sufficiently to increase the initial body-weight somewhat, in 

 order to keep the animals alive. He explains this as due to the 

 gradual exliaustion of available food-substance stored in the 

 various tissues of the body. 



At the end of the various age-periods of the experiment, and at 

 the begmning and end for controls, the rats were killed by 

 chloroform and dissected according to the technique described 

 in previous papers (Jackson and Lowrey '12; Jackson '13, '15 c). 

 The parts, systems and organs were carefully weighed, and 



