70 



HOMOIOTHERMISM 



and growth has computed the times required for various 

 vertebrates to double their weights during early growth 

 and gives the figures shown in Table II. The gestation 

 period of the dog and cat are 56 and 63 days; the com- 

 parable development of the pike requires 574 days. The 

 rate of growth of a dog is comparable to that of a pike 

 after it is dependent on its own resources for the manu- 

 facture of food; i.e., after it has ceased to depend on 

 food supplied by its mother. At 16 deg. C. a mammal 

 requires 800 calories per kilogram of body weight per 

 day; a fish at the same temperature needs only 30.8 kg.- 

 cal. per day. A pike is slower but for the same amount 

 of growth requires about the same amount of energy. A 

 fish weighing 1.75 grams needs 39 calories in 24 hours ; 

 a mouse of the same size needs 997 calories in 24 hours. 

 The mouse consumes 25 times as much as the fish. 



TABLE II 



Time Required for Animals to Double their Weights, 

 AS Determined by Rubner (1924) 



Kubner (1924a) has made further studies which re- 

 late especially to amphibians and reptiles and makes a 

 general comparison between homoiotherms and poikilo- 

 therms. Growth begins with a considerable amount of 

 water in body cells and a variable colloid content. As 

 growth progresses, water gradually decreases. Hor- 



