320 THE HUMAN MOTOR 



Finally, as a precaution, always verify that the zero of the baro- 

 meter corresponds to the level of the point p, and bring the 

 mercury flush therewith by turning the screw. 



If Tissot's spirometer is used, a thermometer immersed in 

 the water will give the temperature, and the barometer will 

 show the pressure at which the gases are measured. 



If the derivation apparatus is used, the temperature of the 

 gases will be, on an average, that of the receptacle in front of the 

 meter, but a certain error in regard to both temperature and 

 pressure is unavoidable. 



246. Knowing the volume of the gases V for the duration of 

 the experiment, and the analysis having given the values of 

 CO 2 and of O 2 , it will be easy to deduce : 



1. The respiratory quotient 2 ,' 



^2 



2. The total oxygen consumed. In the pure inspired air, there 

 is 21% oxygen, and if the analysis gives 17% then 4% has been 

 consumed by the organism. Therefore, the proportion r in the 

 expired gases being determined, the quantity remaining in the 

 body will be : 



(21 -r] x V . 

 100 



3. The total carbonic acid gas eliminated. Here all the CO 2 

 in the expired gases is taken, since there was practically none 

 in the inspired air (0-03%). 



For example, let v be the consumption of oxygen in 10 minutes, 



CO 



of a man in repose, and let -^ = 0-98. This respiratory 



U 2 



quotient indicates a utilisation of carbo-hydrate reserves. A litre 

 of oxygen equals, therefore, 5-05 Cal., and v litres represents the 

 static expenditure of the subject. Then : 

 q s =v Q X 5-05 Cal. 

 Let z;' be the quantity of oxygen absorbed during work equal to 



T for 10 minutes, and let -^ = 0-97. The co-efficient 5-05 Cal. 



will also be applicable to this gross expenditure : 



q = v' x 5-05 Cal. 

 It follows that the dynamic expenditure will be : 



<I<t = ( v 'o *> ) 5 ' 05 Cal - or 9 & 



247. Vital Capacity and Respiratory Rhythm. The vital capa- 

 city ( 79) is measured by the spirometer and the volume reduced 

 to and 760 millimetres. 



The rhythm of the respirations may be traced by Tissot's 

 spirometer, for instance, by fitting the glass tube with a style 



