THE CARBON BALANCE 587 



ticularly when the investigations are undertaken on men doing ordinary 

 types of muscular exercise, such as walking or climbing. It is true 

 that the influence of muscular exercise on the energy metabolism may 

 also be studied by having a person in the calorimeter do exercises on an 

 ergometer, but the results thus obtained are in many ways not nearly so 

 valuable as those which can be secured by observing the respiratory 

 exchange of persons doing ordinary types of muscular exercise in the 

 open. The following table of observations on horses is of interest in this 

 connection. 



It will be observed that the metabolism increases extraordinarily for 

 even a moderate degree of work, but that at the same time the respiratory 

 quotient remains constant. From observations on the respiratory ex- 

 change of working men and animals, extremely important facts concern- 

 ing the efficiency of muscular work have been secured. The form of 

 respiratory apparatus (Zuntz or Douglas) employed for this purpose 

 must be capable of being strapped on the man's back without causing 

 any embarrassment to his bodily movements. By a comparison of the 

 respiratory exchange with the amount of work done, the efficiency of the 

 work can readily be determined. It has been found, for example, that 

 the efficiency is much greater after the man or animal has got into the 

 swing of the work, his energy expenditure per unit of work being much 

 greater during the first half hour's work in the morning than it is 

 later on. This indicates that after a little practice the muscles can ex- 

 ecute a given movement and perform a given amount of work much 

 more smoothly than when they are not in training. Another interesting 

 outcome of the investigations has been to show that work done under ab- 

 normal conditions that tend to produce any kind of muscular strain is 

 done inefficiently. It has been found in marching soldiers, for example, 

 that the slightest abrasion of the foot greatly increases the energy 

 expenditure, for the man, in trying to avoid the pain produced by the 

 abrasion, brings into operation muscular groups that are really not 

 required for the efficient performance of the movement, but are used in 

 the attempt to avoid pressure on the sore. Fatigue also causes inefficient 

 performance of work ; that is to say, the fatigued person, on attempting 



