54 



COMPARISONS OF RESPIRATORY EXCHANGE. 



as follows: The subject of the experiment breathes through a mouth- 

 piece attached to a tee connecting two glass valves which separate the 

 inspired and expired air. The expired air is measured by means of a 

 moist gas-meter. A sample of the air is taken over water by an auto- 

 matic apparatus and is then analyzed in a special gas-analysis apparatus 

 in which the carbon dioxide is absorbed by potassium hydroxide and 

 the oxygen absorbed by phosphorus. 



Mouthpiece. The mouthpiece used, which is shown at C in figures 

 18 and 19, is the original Denayrouse type. 1 It is constructed of soft, 

 pure-gum rubber and consists of an elliptical piece of rubber or flange, 

 having an opening in the center, 2 cm. in diameter, to which a rubber 

 tube is attached. This flange is placed between the lips and gums. 



B 



FIG. 18. Mouthpiece and valves used in the Zuntz-Geppert apparatus. 



Air enters at A, is drawn into the mouth through the mouthpiece C, and is exhaled at B. c, 

 opening which is covered by a membrane; d, inside tube of valve; e, rubber stopper; /.outside 

 cylinder of valve. 



FIG. 19. Most recent form of the Zuntz valves. 



The enlargement in the outside cylinder permits a very free play of the membrane around the 

 inside cylinder, and also serves to hold water for moistening the inspired air and the membrane; 

 air enters at A and leaves at B; C, mouthpiece. 



Two small flanges attached at right angles to the larger flange enable 

 the subject to grasp it with the teeth and thus keep it in place. This 

 type of mouthpiece is the most generally used when mouth-breathing is 

 employed. 



Nose-clip. The nose-clip is also of the type most commonly used, 

 i. e., a flat steel spring consisting of a band of metal about 15 mm. 

 wide, on the inside of which are flat pads which fit against the sides of 

 the nose. The tight closure of the nostrils depends upon the proper 

 placing of the nose-clip and upon the tension of the spring. 



Valves. The valves used are shown in figure 18. A glass tube, with 

 an internal diameter of 22 mm. and a length of 25 cm., is rounded over 



1 P. Regnard, Recherches experimentales sur les variations pathologiques des combustions 

 respiratoires, Paris, 1879, p. 286. 



