192 PLANT PRODUCTS 



deduction for indigestible material (see p. i88), and 

 secondly, the deduction due to the urea produced in 

 place of nitrogen. Further, during the process of diges- 

 tion, bacterial fermentation produces considerable loss, and 

 further there is a loss of energy in production, due to 

 such operations as chewing tough fibres, intestinal move- 

 ment, circulation of the blood, the action of the lungs, 

 etc. It is, however, possible to prepare a balance-sheet of 

 income and expenditure in terms of calories. The following 

 represents the result of a particular experiment on a well- 

 fed ox : — 



Table 24. 



As regards the internal work in the animal, if the heat 

 produced is really required there will be no loss due to the 

 food itself ; but if the heat produced by this work is not 

 necessary, then such energy will have to be considered in 

 the above table under the head of the extra energy for fatten- 

 ing processes. The conditions are much the same as those 

 prevailing in a steam engine. A locomotive " standing in 

 steam '* is roughly reckoned to consume half as much coal 

 as if it were really working, and similarly, the animal takes 

 a good deal of food for mere maintenance, as is exhibited in 

 the table given above. If an animal is fed with more food 

 than is necessary for mere maintenance, a portion of the food 

 will be used for the production of flesh and fat, but the putting 

 on of this flesh and fat will involve a certain consumption 



