310 THE HUMAN MOTOR 



The principle has already been stated. We have to determine 

 the consumption of oxygen, in repose and at work, of a subject 

 placed in an environment of known temperature. 



To avoid uncertainty, it is better to operate in the morning, 

 after the fast of the night (about 10 hours). The calorific power 

 of a litre of oxygen, at and 760 mm., will then be 4-6 cal. ( 110). 



We can also give a certain quantity of carbo-hydrates to the 

 subject and not begin the determination until 2 hours afterwards. 

 In that case the calorific po\\er will be nearly 5 calories ( 101). 



If, finally, the subject feeds as he likes, and it is not possible to 

 submit him to a known diet, we are guided by the respiratory 

 quotient ( 101). The calorific power power is then 4-90 cal. on 

 the average. The experiment should last at least 10 minutes so 

 that the respiratory regimen may become normal. 



239. Measurement of Respiratory Exchanges. In the mouth 



of the subject Chauveau's in- 



- 7 -7 haler is placed, the valves of 



/* ' which combine tightness with 



great mobility. At inspira- 

 tion the external air opens 

 the valve I and passes to the 

 lungs ; at expiration, I closes 



Chauveau's respiratory valve. and the gasses pass through 



the valve E, an indiarubber 

 tube leading them to the meter ( figs. 217 and 218). 



FIG. 218. Chauveau's respiratory valve. 



The part of the valve B, which enters the mouth, has a ring of 

 indiarubber which fits against the teeth, under the lips, and 

 prevents any leakage. The nose is pinched by a clip in the form 

 of a small wooden clothes peg covered with felt. Before the 

 experiment, the parts of the valve are carefully cleaned to prevent 



