16 



University of New Hampshire 



[Sta. Bull. 331 



or absorbing- food the collective activity of the cells represents basal 

 metabolism which is minimum tempo at which this biological engine 

 can function without stalling. The basal metabolism is therefore 

 merely the persistent minimum effort necessary to keep alive. Bio- 

 logically the energy expended in basal metabolism, or idling of the 

 animal motor, can be regarded as the maintenance requirement. As 

 a functional expression it also represents the internal adaptation of 

 organs, glands, etc.. for the potential conversion of energy, that is. 

 the comparative ""horsepower" rating of this biological motor. 



This is illustrated in Fig. 6 by the contrast in internal adaptation 

 to function as represented by the size of thoracic cavity or container 

 of heart and lungs (i.e. power plant) in relation to external circum- 

 ference and thickness of flesh. 



eii^ 



FIGURE n. EVEX SLOW PLODDING WORK INCREASES ENERGY EXPENDITURE 



TEN FOLD OVER RESTING 



Basal metabolism or energy expenditure thus has physiological 

 importance to the individual, but in domestic animals it contributes 

 nothing to our own welfare. Economically its value is nil. From the 

 economic point of view animal life really begins here with its innu- 

 merable activities. Categorically we let in the clutch on the idling- 

 motor, fuel (i. e. food) consumption goes up and the animal begins to 

 carry out those economically important ftmctions to which its in- 

 ternal adaptation is designed. 



By selective breeding we have developed animals of many types, 

 and with highly specialized functions far beyond those possessed by 

 their feral ancestors. 



In every class of farm livestock, even including poultry, we have 

 thus created breeds with contrasting adaptations in regard to the 

 use which they make of food energy. In the adaptation of these 

 specialized functions for utilizing food energy they may be regarded 

 as representing three general classes. The beef type stores energy 

 as body tissue, the dairy type secretes it as milk, and the horse burns 

 it up in work, either by a burst of muscular speed for short duration 



