194 PLANT PRODUCTS 



about one-half the weight is removed, the ultimate advantage 

 of such treatment is not very marked, although it does 

 undoubtedly show that if the ox is assisted in his digestive 

 process, a larger amount of energy will be left for him to 

 make some good use of. In a similar way, merely chaffing 

 straw or hay reduces the work necessary to be done by the 

 beasts, and, therefore, a higher feeding value can be obtained. 

 When animals are merely maintained in store condition 

 the amount of food necessary to keep them is small, and may 

 be of a coarse quality, since the energy expended in chewing 

 is useful for maintaining the temperature. If, however, 

 animals are called upon for a big output of energy, they must 

 be fed on foods which do not involve so much internal 

 expenditure. A horse that is doing nothing can live upon 

 hay and grass, but the harder the work given, the greater 

 must be the proportion of concentrated foods. If the external 

 work is to be increased, the internal work must be decreased. 

 The same remark applies to cattle and sheep. The relation- 

 ship between the amount of calories necessary for maintenance 

 and the live weight is not constant, but depends upon the 

 size of the beast. Roughly speaking, the loss of heat from 

 an animal body is proportionate to the surface, though the 

 amount of hair and fur will effect this considerably. The 

 theory, however, that the amount of heat is proportionate to 

 the surface is surprisingly close to what is obtained in practice, 

 although it is very easy to push the theory too far. If 

 the " surface law " is considered, it will be seen that the 

 weight of a beast will vary as the cube of the length, whilst 

 the surface will vary as the square of the length. Hence, a 

 small increment in the weight of the beast corresponds with 

 two-thirds of that small increment in the food. 1 



But as a beast grows older its digestion diminishes, and 

 more food has to be fed to counteract the decrease in 

 digested nutriments, hence the common rule of reckoning 



1 Since w *>l 3 , /eosoo/*eo w l 



where w=weight, /= length, /= food, s=surface. 



