256 COMPARISONS OF RESPIRATORY EXCHANGE. 



the nostrils, the pressure against the nostril being regulated at will. 

 This noseclip may be worn for a long time without discomfort. 



That the breathing with the mouthpiece is not abnormal was shown 

 in the comparison experiments carried out in this research with both 

 the Benedict apparatus and the Tissot apparatus, in which mouth- 

 breathing and nose-breathing were compared. The results obtained 

 with the two methods of breathing were practically the same. 



MASK. 



The mask has been used in this research in a very few experiments, 

 but only for the purpose of studying the effect on the respiratory 

 exchange of this method of breathing. 1 In the earlier use of the 

 Benedict respiration apparatus, a rubber mask was employed which 

 was held against the face by binding-strips of leather and tape. A 

 pneumatic ring around the edge could be inflated when the mask was 

 in position. In this research, however, a mask of lead and plasticene 

 was used, similar to that employed by Bohr. 2 



With the mask the subject can breathe at will through the mouth or 

 the nose and is not obliged to concentrate his mind upon keeping his 

 mouth closed or taking care that the mouthpiece does not slip out of 

 position. With this form of breathing appliance, however, it is much 

 more difficult to prevent the escape of air than with either the mouth- 

 piece or the nosepieces. The subject must hold his head practically 

 rigid, as the slightest movement may cause a leak and a consequent 

 loss of the whole experiment. The mask can not be used with a subject 

 having a beard and a separate mask must be made for each individual. 

 Furthermore, the air inside the mask acts as a dead space and increases 

 the depth of the respiration. Some of the subjects have also com- 

 plained that the air seems warm and stagnant inside the mask. 



From our experience in this laboratory it does not seem advisable 

 to use a mask and either the nosepiece or the mouthpiece is preferable 

 from the standpoint of both the mechanical manipulation and the 

 comfort of the subject. This is especially the case when many subjects 

 are being used, particularly if they are not very much interested in the 

 experiments. In experiments in which the investigators themselves 

 are the subjects, it may be perfectly practicable to use a mask. In 

 such experiments, however, the edges of the mask should be tested 

 with soapsuds to make sure that no leaks occur. The mere fact that 

 no leak is perceptible when pressure is used inside the mask is not an 

 absolute proof of the absence of a leak, as the pressure inside the mask 

 may tend to make the closure more perfect. 



In general, it may be stated that the mask is the least preferable of 

 the breathing appliances. The mouthpiece is the most reliable from 



1 See p. 189 for description of masks and results of experiments. 

 1 Bohr, Deutsch. Archiv f. klin. Med., 1907, 88, p. 385. 



