496 THE EFFICIENCY OF THE ORGANISM 



other hand, is the vahie obtained as the result of dividing the heat 

 equivalent of the external effective muscular work by the total 

 energy output of the individual during the period in which the 

 work was done. The table on p. 495 will make the point clear. 



It is obvious that the two efficiencies may give very different 

 values. The gross efficiency, which is largely influenced by the 

 amount of work performed during the day and the amount of 

 time which is actually expended in doing work, as a physiological 

 measure gives little or no information regarding the capacity of 

 the human body for work, and certainly no conception of the 

 possibilities in the way of the efhciency of the organism as a 

 machine. The net efficiency, which is determined by the deduc- 

 tion of the maintenance quota from the work quota of the energy 

 output, does give the actual increase in cost necessitated by the 

 performance of the external muscular work and thus permits of 

 the determination of the actual physiological efficiency of the 

 organism. 



In view of the fact that engineers and others ha^'e found it 

 a comparatively simple matter to determine the efficiency of 

 ordinary thermodynamic machines })y the use of a simple formula 

 E = (Tj — T<y)lT^, where T^ is the absolute temperature at the 

 source of the heat (the steam in the boiler in the case of an engine) 

 and To the temperature at the sink (the condenser of the engine), 

 there has been a great temptation to apply the apparently almost 

 universal rule of the Second Law of Thermodynamics to the living 

 organism (Chap. IV.). It is, however, obvious from a very brief 

 consideration of the above simple thermodynamic formula that 

 the efficiency is simply a function of the difference of potential, 

 the higher the temperature at the source and the lower the tem- 

 perature at the sink the greater is the efficiency. Now the 

 efficiency of the living organism has experimentally been shown 

 to be high, probably over 30 per cent., a result which would 

 necessitate an impossible difference of potential in the tissues. 

 It is perfectly true that this difficulty has been appreciated, but 

 it is not solved, except on paper, by positing minute points of 

 enormously high temperature alternating with points of low 

 temperature at intervals of a fcAv ju, (10-=^ nmi.). The mechanism 

 of muscular activity, it is true, is not >et clear, but it may be 

 stated with a considerable degree of certainty that, whatever the 

 type of change which takes place, all the experimental evidence 

 available points to the muscle not being a heat engine. The 

 majority of workers now look upon muscle as a chemical machine 

 which works at a relatively constant temperature. 



On the purely experimental side much work has been done on 



