UTILISATION OF NUTRIENTS 47 



therefore, 672-5 - 22-8 = 649-7 g r - carbon over. 

 With the exception of fat the other nitrogen-free 

 carbon compounds in the body are only formed in 

 very small quantities, so it is permissible to reckon 

 all the added carbon — 649-7 gr. as fat. It is known 

 that 100 parts beef suet contain 76-5% carbon, so 

 that 649-7 gr. of carbon = 849-3 gr. (nearly 2 lbs.) 

 of fat added each day. 



Investigations of this kind are carried out exactly 

 as was described in the case of increase of flesh, but 

 the animal must become used not only to having 

 no litter, but also to the respiration chamber, before 

 the experiment begins. Such an experiment takes 

 at least twelve to fourteen days, during which time 

 the faeces and urine must be collected daily without 

 loss. The products of respiration are estimated 

 three or four times for periods of twenty-four hours 

 exactly. In such investigation the digestibility 

 of the food is naturally determined in addition to 

 the nitrogen and carbon metabolism. 



As has already been stated, the digested nutrients 

 not only supply material for the formation of 

 flesh, fat, wool, milk, etc., but they also serve as 

 carriers of heat and energy, both of which are re- 

 quired by the body. Investigations on the energy 

 relations of the body are most important, and it 

 will be well to briefly note the methods by which 

 the energy metabolism of an animal is ascertained. 



