CRITICAL DISCUSSION OF RESPIRATION APPARATUS. 255 



It is quite possible that the exact shape of the nosepieces has not yet 

 been rightly determined. 



These glass nosepieces can also be tested by the use of soapsuds. 

 The use of pressure for testing is not, however, generally practicable, 

 as the nosepieces are not dilatable and allow the air to escape between 

 the glass and the nostril when pressure is put on the inside, thus 

 practically enlarging the nostril without enlarging the nosepiece. 



MOUTHPIECE. 



While the mouthpiece 1 has been more or less employed in this 

 research, the pneumatic nosepieces have usually been preferred. 

 Three objections are made to the use of a mouthpiece, i. e., that the 

 subjects do not like it, that constant care is necessary to prevent the 

 escape of air, and that abnormal breathing may possibly result from its 

 use. 



The mouthpiece is not so agreeable as the nosepieces, for the thick 

 piece of rubber used for the flange and held between the teeth and lips 

 excites a flow of saliva in the mouth which is often extremely annoying 

 to the subject. Furthermore, to prevent an escape of air, the subject 

 must draw his lips up closely around the circular tube. There is a 

 natural tendency to relax this firm closure of the lips and air may thus 

 escape between the corners of the mouth and the rubber flange of the 

 mouthpiece. The absence of leaks may be determined by using soap- 

 suds, as with other breathing appliances. This was admirably demon- 

 strated in a research on muscular work carried out by Benedict and 

 Cathcart, 2 in which the subject rode a bicycle and breathed through the 

 mouthpiece into the respiration apparatus. In this series of experi- 

 ments it was absolutely imperative that there should be no uncertainty 

 regarding the measurement of the oxygen consumption. The only loss 

 of air possible was about the mouthpiece, and soapsuds were constantly 

 used over the mouth. That the loss of air was possible was proved by 

 the fact that occasionally a small bubble formed in the soapsuds; 

 when cautioned by the observer, however, the subject closed his mouth 

 tightly and thus no leak occurred. With the mouthpiece it is easier 

 to make sure that the closure is perfect, for if the subject keeps his lips 

 drawn closely about the central tube there is very little, if any, proba- 

 bility of a leak. 



When the mouthpiece is employed, the nose can easily be closed by 

 means of a nose-clip. Most of the nose-clips used give great discomfort 

 after they have been worn throughout the experimental period. The 

 most comfortable nose-clip and the one commonly used at the present 

 time is that made by Siebe, Gorman & Co. This is provided with a 

 thick felt pad and is so constructed that it fits closely to the outside of 



x See description of type used on p. 54. 



"Benedict and Cathcart, Carnegie Inst. Wash. Pub. 187. 1913. 



