184 THE HUMAN MOTOR 



however, the expenditure is almost uniform ( x ) and can be 

 measured. Finally, if a stoppage of work takes place, the ex- 

 penditure does not fall back to its static value, but is maintained 

 longer the higher it has been raised, that is to say, the more 

 intense has been the work. The law of repose takes the same 

 course as Newton's law for the cooling of hot bodies. ( 2 ) This is 

 very important, because rapid work, besides being economical, 

 will also be the least persistent in its after effects. ( 3 ) The pro- 

 portion of CO 2 to Ojj becomes higher and the respiratory quotient 

 therefore increases. ( 4 ) 



All these disturbances which affect the exchanges of gas seem 

 to affect the elimination of carbonic gas much more than the con- 

 sumption of oxygen, and under normal conditions it can always 

 be assumed that the oxygen gives the most correct measurement 

 of the energetic expenditure. 



127. The rate of the expenditure varies at different hours of 

 the day, the minimum taking place from 3 to 7 o'clock in the 

 morning for a man in repose or a man at work ( 105 and 106). 

 On the other hand, partaking of meals raises the expenditure in 

 a proportion which is modified by the nature of the nutriment. 



By beginning from the time of the meal it is possible to find the 

 moment at which it no longer has any appreciable influence on 

 the rise of the expenditure and to see whether the time 

 elapsed is independent of the nature of the nutriment. The 

 procedure is as follows : The subject fasts from 8 o'clock in the 

 evening, to 8 o'clock in the morning and then takes a carbo- 

 hydrate meal, his exchanges of gas, whilst fasting, being previously 

 measured for five minutes. From the moment of the meal, 

 similar measurements of the consumption of oxygen are made 

 from hour to hour. 



Similar determinations can be made after a nitrogenous meal. 



A series of similar experiments were carried out with the 

 experimental bicycle, work equivalent to 2-72 Calories being 

 performed in 10 minutes. The subject was fed both with 

 carbo-hydrate and nitrogenous diets, and tests were made for 

 various intervals of time between the meal and the work. 



These results may be summarised as follows : 



1. The rise of the expenditure following a meal ceases at once 

 if the latter is of carbo-hydrates ; the expenditure, in other cir- 



(*) Jules Amar (Ibid., p. 892 ; Le Rendement de la Machine Humaine, 

 pp. 64-5, Paris, 1910). 



(') Ibid. (Comptes Rendus Sciences, vol. cliii., p. 79). 



( 8 ) The measurements of Atwater on the energetic expenditure at 

 intervals of two hours ( 105) confirm the law of repose. 



(*) Katzenstein (Pfluger's Archiv., 1891, vol. xlix., p. 330). 



