PRINCIPLES THAT GOVERN FEEDING 171 



passing it may be said that the following are chief among 

 the influences concerned in such regulation: (i) The kind 

 and amounts of the food fed; (2) the temperature to which 

 animals are exposed; (3) the warming of food and drink 

 taken into the stomach; (4) the amount of the muscular ex- 

 ertion allowed or demanded; (5) the conduction and radia- 

 tion of heat from the skin; and (6) the evaporation of 

 water from the skin and lungs. 



Muscular exertion may be classed as external and in- 

 ternal. The former is the muscular exertion called for in 

 effecting the movements concerned in the various vital 

 processes within the body. The latter is the muscular exer- 

 tion called for by animals when exercising or performing 

 physical work. The relation between these is very close. 

 Of whatever kind it may be, it calls for a constant supply of 

 heat to maintain it, and the greater the exertion, of course 

 the greater the supply of heat demanded. Of course this 

 heat must all come directly or indirectly from the food. Be- 

 yond this, the relation between food supply and muscular 

 exertion is not well understood. It is certain, however, 'that 

 the food given to the animal to support muscular exertion 

 must be something more than fuel, that is, it must be partly 

 nitrogenous and it must be liberal in supply. Stated in sum- 

 mary : ( i ) Muscular exertion is dependent on the food sup- 

 ply; (2) the greater the exertion to be made, the greater 

 must the food supply be; (3) the greater the exertion, the 

 greater also must be the proportion of the nitrogenous sub- 

 stance in the food. 



Food or feeding ration. The term food or feeding ra- 

 tion more commonly means a combination of the food fac- 

 tors used in feeding animals in any given instance, but 

 sometimes it may mean but one food factor. When the 

 proportion of the nitrogenous and non-nitrogenous nutri- 

 ents are present in a food ration in that degree that will 

 best effect the ends sought when fed, it is said to be in bal- 

 ance (see p. 172). When not fed in balance waste in some 



