8 APPLIED PHYSIOLOGY 



quantity of protein food during training merely to make 

 good wear and tear. 



We may now pass on to consider the other great 

 function of metabolism 



2. The Conservation of Bodily Energy. 



1. Expenditure of Energy. By means of experi- 

 ments with the respiration calorimeter the daily ex- 

 penditure of energy in the body can be calculated 

 without much difficulty. The chief items of expenditure 

 are these : (i.) internal work (heart, respiration, heat 

 production, secretion, excretion, etc.) ; (ii.) digestive 

 work ; (iii.) external or muscular work. 



The expenditure of energy in the performance of 

 mental work cannot be calculated, and, indeed, external 

 work is the only item which can be estimated with any 

 accuracy. 



(i.) By internal work is meant all the work which is 

 required for carrying on the chief vital processes of the 

 body, without which life would be impossible. The work 

 of the heart alone amounts to about 20,000 kgm. 

 (133 Calories),* or about 64 foot-tons, per day. In 

 diseased conditions, in which the work of the circulation 

 is carried on with difficulty, this amount may be very 

 largely increased (see Chapter IV.), and may become so 

 great, indeed, that no margin of available energy is left 

 for any form of external work. A patient in such a 

 condition is thus inevitably condemned to a life of com- 

 plete inactivity. The work performed by the muscles 

 of respiration in elevating the chest amounts to about 

 * Allowing for heat produced as well. 



