38 



ARON. 



no real tendency to grow. They follow the skeleton whenever the nutri- 

 tion is favorable enough to permit such growth, and the conclusion could 

 be drawn that their growth is controlled rather by mechanical forces 

 (traction) than by an internal force (tendency to grow). 



ENERGY REQUIRED DURING GROWTH. 



A short discussion of the behavior of the dogs which were amply fed is 

 also necessary. For the purpose of calculating what fraction of the 

 energy taken with the food was used for growth, we will take the average 

 weight of the dog as a basis for the calculation of the energy required for 

 maintenance. The excess of calories over this amount can be regarded as 

 being used for the production of new body substances in a more or less 

 economic way. As "optimal growth" we may term with Eubner the 

 condition under which the greatest percentage of this excess of calories is 

 transformed into new body substances. Fo one of our dogs probably was 

 at this stage of optimal growth, but all of the animals were more or 

 less overfed, and hence the number of calories used for the fomration of 

 1 gram, of new body substances was higher than at the stage of optimal 

 growth. 



I have calculated, in the way just described, the number of calories 

 used for the production of 1 gram of new body substance for certain 

 periods of our experiments. It seems advisable as a basis for such cal- 

 culations to take periods as long as possible, in order to reduce the un- 

 avoidable error due to the daily variations of the live weight. The 

 values obtained vary from about 1.6 to 4.6 calories (see the following 

 table). The higher values, 3 to 4 calories, are found when the animal 

 is amply fed and toward the end of an experiment when the animal 

 is older. This will easily be understood if we assume that under these 

 circumstances there is a relatively greater deposition of fat tissue, rep- 

 resenting a higher caloric value. 



Number of calories used for the production of 1 gram of new body substance 



in dogs. 



Dog No. 



In 

 days. 



From— 



To— 



Daily in- 

 crease in 

 weight. 



Energy 

 in food. 



Energy 



for 

 mainte- 

 nance. 



Differ- 

 ence. 



Energy 

 consumed 

 for 1 gram 



growth. 



I. 



20 

 10 

 10 



Grams. 

 2,660 

 2, 290 

 2,670 



Grams. 

 3,380 

 2,670 

 2,950 



Grams. 

 69 



28 

 28 



Calories 

 425 

 840 

 340 



Calories 

 250 

 210 

 230 



Calones 

 175 

 130 

 110 



Calories. 

 2.6 

 4.6 

 4.0 



IV 



IV 



C 



3.5 

 30 



2, 700 

 1,715 



3,340 

 2,250 



18 

 15.5 



300 

 225 



245 

 170 



55 



55 



3.0 

 3.5 



B _ _ 





VIII 



XII 



50 

 50 



1,265 

 1,572 



2,015 

 2,532 



15.6 

 •19.0 



190 



215 



165 



185 



25 

 30 



1.6 

 1.6 



