266 VETERINARY PHYSIOLOGY 



an animal is a difficult matter. It can be estimated, how- 

 ever, from the weight. Since, for animals of the same species 

 and type, the factor " k " is constant, the basal metabolism 

 is proportional to two-thirds the power of the weight and can 

 be compared on that basis. Thus, for example, if an animal 

 of 1000 lbs. live weio^ht has a basal metabolism of 7000 

 Calories, another of the same species and type, of 1500 lbs. 

 would have a basal metabolism of approximately 



7000 X (UUf, i.e. 9172 Calories. 

 2. Age. — In the young animal not only is energy required 

 for growth, but the active tissues of the body are in greater 

 jDroportion than in the full-grown animal. Actual measure- 

 ments in the calorimeter have shown that the basal energy 

 requirements of a boy of ten years of age are about 25 per 

 cent, greater per unit of surface area than those of the adult. 

 A similar relative increase doubtlessly exists in all young 

 animals. The influence of age on metabolism and the 

 energy requirements of growth have not, however, been 

 fully investigated. 



II. Factors modifying the Metabolism. 

 1. Muscular Activity. 



Since the energy for muscular work comes ultimately 

 from the processes of oxidation in muscle, the rate of meta- 

 bolism varies with the amount of work done, and with the 

 rate at which it is done. 



Tills is by far the most important factor determining 

 the extent of metabolism and the energy requirements of the 

 individual. Under the influence of muscular work a tenfold 

 increase has been observed in man. In the horse, with its 

 great muscular development, an even greater increase is 

 doubtless sometimes obtained. 



The close parallelism between muscular activity and 

 energy expenditure is remarkable. Movements which are 

 scarcely noticeable, and even increased tonus of muscle 

 apart from motion, are accompanied by an appreciable rise 

 in the rate of metabolism. Thus a soldier standing rigidly 

 at attention may expend 10 per cent, more energy than 



