46 HOMOIOTHERMISM 



nal amount after seven months without food. At first 

 protein, carbohydrate, and fat were oxidized equally, but 

 after a time the carbohydrate was exhausted and fat, 

 though present in small quantity, was not used up 

 (Moore and Herdmann, 1914). Starved centrachid fishes 

 lost about one-third of their body weight in two months, 

 but their fat did not fall below .43 per cent of their net 

 weight at the end of the experiment (Pearse, 1925). A 

 starved trout lost one-fifth of its body weight in four 

 weeks at the expense of its protein content. Frogs dur- 

 ing starvation did not decrease in weight because of the 

 accumulation of water in their lymph spaces. Most of 

 their organs decreased in weight, but the integument, 

 brain, spinal cord, eyeballs, spleen, kidneys, and testes 

 did not (Ott, 1924). Hibernating woodchucks lost about 

 3.25 grams per kilo during 110 days (Easmussen, 1917). 

 In a starving mammal glycogen spares protein if it is 

 available. The nitrogen output decreases during a pro- 

 longed fast in a fish or a mammal. This indicates a 

 decrease in metabolism. There is no doubt that such a 

 decrease takes place, for not only does nitrogen excre- 

 tion decrease, but the oxygen intake and carbon dioxide 

 output is also reduced. 



Glands, Enzymes, and Hormones. — The general 

 scheme for the maintenance and control of metabolism 

 appears to be quite similar in homoiotherms and poikilo- 

 therms. A fish (Knauthe, 1898) or a turtle (Pearse, 

 Lepkovsky, and Hintze, 1925) requires a certain balance 

 in its food ration and this is apparently quite similar to 

 that which is essential for the proper nutrition of a bird 

 or a mammal. Frogs when fed on white bread develop 

 beri-beri and recover from the disease when supplied 

 with a variety of fruits and insects (Hoffman, 1926). 

 The digestive enzymes of fishes, salamanders, frogs, tur- 



