254 COMPARISONS OF RESPIRATORY EXCHANGE. 



soapsuds in this manner through the experiment also requires the 

 constant attention of at least one assistant during the entire period. 

 Unless the nosepieces are tested throughout the whole experiment, it is 

 possible, after the experiment has begun, for a leak to occur which may 

 give inaccurate results with a closed-circuit apparatus, although the 

 presence of the leak may not be positively known. As the pneumatic 

 nosepieces deteriorate somewhat rapidly and require constant care to 

 make sure that they are in perfect condition, they must be tested 

 under water immediately before the beginning of each day's work, for it 

 has at times been found that nosepieces which have been perfect on the 

 night preceding the experiment may leak when used the next morning. 



Occasionally a nosepiece slips out of place during a period. They 

 also have a tendency to cause a mucous secretion in the nostril, which 

 clogs the nose and interferes with the breathing. In several instances 

 it has been necessary to use the mouthpiece instead of the nosepieces 

 for this reason. When the nostril is exceedingly small, a smaller 

 nosepiece has to be used and the opening may not be large enough for 

 free respiration, so that an actual impediment to the breathing may 

 result. Although these nosepieces are extremely flexible, they will 

 not fit in every case, as the opening of the nostril varies markedly with 

 different people. With some individuals it is practically impossible to 

 make a circular-shaped nosepiece fit the nostril, as the opening of the 

 nostril is not round, but long and narrow, with a point at each end. This 

 makes it extremely difficult to find any kind of a nosepiece which will 

 fit closely without leak. 



In general the pneumatic nosepieces have found the widest applica- 

 tion in this laboratory, because they are adaptable to most subjects and 

 the most comfortable appliance to use. In our experimenting we have 

 not found more than 10 subjects who were unable to use these nose- 

 pieces, and with only a small proportion of those who used them was 

 soapsuds applied for the detection of possible leaks. 



GLASS NOSEPIECES. 



The glass nosepieces described by Tissot 1 have been more or less 

 employed in this research. They are always ready for use, practically 

 indestructible with proper care, can be made in a large variety of sizes, 

 and give a good opening for free breathing. On the other hand, as 

 the round glass nosepieces when inserted are parallel to one another, 

 the enlarged part of the glass presses against the cartilage between the 

 nostrils and this pressure becomes exceedingly painful after a time. 

 An attempt has been made to remedy this by making glass nosepieces 

 with an oval instead of round cross-section, since this would conform 

 more generally to the usual shape of the opening of the nostril; but the 

 oval nosepieces have not proved so successful as had been expected. 



'See description on p. 62. 



