18 APPLIED PHYSIOLOGY 



to remain thin, for they need to produce so much heat 

 that there is no margin left for storage as fat. 



Again, a man of large muscular development has a 

 more active metabolism than one whose weight is to a 

 great extent made up of fat ; for muscle is a ' vital 

 tissue, whereas fat is, comparatively speaking, ' dead.' 

 On the other hand, the mere carrying about of a stone 

 or two of fat increases considerably the mechanical task 

 of the muscles of locomotion in a stout man. There is 

 thus a sort of automatic check upon indefinite increase 

 of stoutness, for beyond a certain point the greater 

 expenditure of energy required for locomotion will use 

 up all the surplus intake in the form of food. 



3. Influence of Work and Rest. The large share of 

 the daily expenditure of energy in the body which is 

 due to external or muscular work has already been 

 pointed out, and it will readily be understood that 

 variations in the amount of work performed have more 

 influence upon the total turnover of energy than any 

 other single factor. It has been calculated that the 

 following amounts of energy must be supplied to meet 

 the requirements of varying degrees of muscular work in 

 the case of a man of about 10 stone weight (Magnus- 

 Levy) : 



Calories. 



At rest in bed 2,000 



Eesting indoors ... 2,230 



With light industrial work 2,600 



With moderate muscular labour ... 3,100 



With severe muscular labour ... ... 8,500 



The greatest economy of energy is attained by keeping 



