THE ECONOMY OF MOVEMENT. 



units of other forms of energy, for example, as so many units of 

 heat, or calories. That this must, unfortunately, be the case 

 one realises at once from the fact that we are not yet suffi- 

 ciently acquainted with the exact mode of motion of the 

 constituent masses of the body and limbs to make out the 

 statement of movement in an exact algebraical fashion. It is 

 impossible, then, to go further in this direction than to say 

 that such and such movements were performed with such and 

 such rates of repetition. Thus the credit side of the balance- 

 sheet contains two fractions, one being a statement of this 

 kind with regard to the movements made, and the other a 

 more exact statement of the external work in definite measured 

 units of energy per unit of time. 



With regard to the debit side of the balance-sheet, the 

 " cost " incurred — and necessarily almost simultaneously 

 paid — there is no such complication, since both " movement " 

 and external work are paid for in exactly similar coin. It has 

 been shown by painstaking and elaborate scientific effort that 

 no payment is made for either in other coin than unit of oxida- 

 tion. Expense then is always expressible either in terms of 

 fuel utilised, or oxygen absorbed, or products of oxidation 

 emitted. It is obvious, of course, that each kind of fuel will 

 provide somewhat different sums of energy, but there are not 

 many kinds of fuel available in the body, and it is possible, 

 by an adequate, but quite simple, examination of the products 

 of oxidation emitted, to recognise just what kind of fuel is 

 being utilised at each moment dealt with. Indeed, it is possible 

 to do this without further data than the amount of carbon- 

 dioxide emitted and oxygen absorbed. The ratio between these 

 two quantities is known as the " respiratory quotient," and 

 from this " respiratory quotient " it is now possible, as the 

 result of fundamental experiment, to distinguish the kind of 

 fuel utilised, and to assess the energy liberated by its oxidation. 

 Thus, if the amount of oxygen absorbed per unit time, and the 

 value of the " respiratory quotient " are known, it is possible 



