AVAILABILITY OF ENEBGY FOR CARNIVOBA. 



27 



shown that what is true of the feeding stuffs consumed by horses and 

 cattle is also true of nearly pure nutrients fed to dogs. With these 

 subjects it is possible to use the fasting state as the basis of compari- 

 son, which considerably simplifies the investigations. The experi- 

 ments were made at a comparatively high temperature, namehy, about 

 33° C., a fact which is of importance, as will appear later, in the inter- 

 pretation of the results. 



An experiment in which nearly enough fat was fed to supply the 

 requirements of the organism for energy gave the following results 

 per kilogram live weight, stated in a form which is somewhat differ- 

 ent from that used by Rubner but which in substance is identical 

 with it : 



Availability of energy of fat — Rubner. 





Metaboliz- 



able 

 energy of 

 feed per 

 kilogram 



live weight. 



Loss by 

 body per 

 kilogram 

 live 



weight. 





Calorics. 

 53.4 

 



Calories. 

 7.5 

 54.0 







53.4 

 87.08 



46.5 









This result appears somewhat remarkable in view of the fact that 

 the comparison is virtually with body fat. Literally interpreted, it 

 means that the energy of feed fat is only 87 per cent as valuable as 

 the energy of body fat plus a little protein. If this be true, it implies 

 a larger expenditure of energy in the digestion of fat than now seems 

 probable, since the katabolism of resorbed feed fat can hardly differ 

 greatty from that of body fat. Rubners figure is the result of a 

 single experiment and unfortunately it enters into the computation of 

 all the other results. A redetermination of this factor is much to be 

 desired. 



In two other experiments, lean meat nearly equivalent to the main- 

 tenance requirement was fed. The meat contained a small amount of 

 fat, the average metabolizable energy of the feed per kilogram live 

 weight being distributed as follows : 



Calories. 



In protein 56. 7 



In fat 4.95 



61. 65 



