UTILISATION OF FOOD AND ENERGY 105 



periment on a horse. The animal received, during 

 the whole time, a food which was very rich in 

 protein (7-5 kilos meadow hay and 4 kilos beans), 

 and during the first part of the experiment it had 

 only light work to perform. The -average amount of 

 nitrogen found in the urine daily was 198*6 gr. for 

 a period of fourteen days. The work was then 

 trebled and represented a hard day's work. During 

 the twenty-four days this part of the experiment 

 lasted the daily excretion of nitrogen rose until it 

 reached 243-3 gr., an increase of 447 gr., which is 

 equal to 280 gr. protein or flesh. The live weight 

 of the horse sank in this time from 496-8 to 458-0 

 kilos, which is a decrease of 38-8 kilos. When, at 

 the conclusion of this period of increased work, a 

 return was made to the original light work, the 

 excretion of nitrogen sank to the original amount. 

 The extra work had therefore caused an increase 

 in the nitrogen excreted. Where only light work 

 was being performed the food sufficed, but when 

 the former was trebled the food was no longer 

 sufficient, and body tissue (fat and flesh) had to be 

 consumed. As long as there was plenty of fat 

 present this would be drawn upon and furnish 

 energy, but the less the reserve of fat became, so 

 much more would the body protein be called upon 

 to supply energy for the purposes of muscular work. 

 The protein was thus capable of furnishing part of 

 the energy demanded by the animal. 



