CHAPTER XIII. 



RESPIRATORY EXCHANGE IN MAN. (TISSOT- 

 CARPENTER METHOD).* 



The principle of the method consists in the collection of a 

 definite volume of expired air in an accurate spirometer and the 

 subsequent analysis of a mixed sample of it. It is then possible to 

 compute the energy metabolism (Indirect Calorimetry). After 

 correcting for temperature and pressure, the total CO2 output and 

 O2 intake, and from them R.Q., are then computed. 

 Experiment 50. -The subject sits on a chair and takes the mouth- 

 piece A (Fig. 33) of the respiration tube in his mouth. The 

 mouth-piece consists of an elliptical rubber flange with a hole 

 in the centre connected with the respiration tube. Two rubber 

 lugs are provided and these are gripped between the teeth, the 

 flange being placed between the lips and the gums. The nose 

 is tightly closed by a suitable clamp. 



The RESPIRATION TUBE leads to the valves, B, (Douglas' or Pearce's), the 

 end of the expiration tube of which leads to a large stopcock, C, connected 

 with the interior of the spirometer. The latter consists of a 100-litre inverted 

 aluminium cylinder, D, suspended from a pulley, E, in a water bath between 

 the double walls of an upright stationary cylinder, F. As the aluminium 

 cylinder rises out of the water on account of air entering it, its weight be- 

 comes greater. To allow for this, the wheel is made excentric, (G), so that 

 as E revolves, with elevation of the spirometer, a weight connected by a 

 thread to the circumference of the excentric exercises a progressively greater 

 pull on the spirometer, and so exactly counterpoises it. The top of the 

 cylinder is provided with holes for the insertion of a thermometer and of a 

 tube and stopcock for drawing off the sample of air for analysis. 



*Since the main thing to be learned in this observation, apart from the methods 

 of analysis of the air, is the method of calculation of the respiratory quotient 

 and of the total respiratory exchange, the experiment can be profitably assigned 

 to a larger group of students than the usual. After the sample of air has been 

 collected, certain members of the group will proceed to analyse it and make the 

 necessary calculations. Since the greatest cause for delay in this experiment is in 

 the analysis of the oxygen in the air sample, this procedure should be practised 

 before starting the experiment, and a student who has already had experience 

 with the gas burettes should demonstrate the technique to others. 



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