MASK AND NOSEPIECES, BENEDICT APPARATUS. 191 



to mask to press it more closely to the face. Pulse-rate very regular. Aver- 

 age respiration-rate previous to experiment, 17 per minute. 1 During experi- 

 ment, respiration somewhat irregular. In first period with mask, it was rapid 

 and deep at first, but became slower and more shallow in the middle of the 

 period; in second period with mask it was fairly regular at the beginning, but 

 during the last half it was very irregular and there was considerable apnoea. 

 Portions of the records obtained are given in figure 50, showing the two types 

 of respiration. In the last period with the mask, the respiration was very 

 much like that in the preceding periods. In the periods with the nosepieces, 

 the respiration was much more regular than in those with the mask. Average 

 barometric pressure, 762.1 mm.; average temperature of the air in the appa- 

 ratus, 21.0 C. 



DISCUSSION OF RESULTS. 



The results of this series of comparisons are given in table 33. The 

 summary of the results shows that on the average there is practi- 

 cally no difference in the respiratory exchange with the two methods of 

 breathing, only the total ventilation and the volume per respiration 

 indicating any appreciable differences. The variations in the indi- 

 vidual experiments are not in any case very large. With M. J. S. 

 on July 20, the carbon-dioxide elimination was 8 c.c. lower with the 

 mask than with the nosepieces. With L. E. E. on November 18, the 

 carbon-dioxide elimination was 10 c.c. and the respiratory quotient 

 0.045 lower with the mask than with the nosepieces, but in two of the 

 periods with the mask there was irregular breathing and apncea; con- 

 sequently the carbon-dioxide values are not strictly normal. In 

 practically all of the experiments the ventilation per minute was higher 

 with the mask than with the nosepieces, but as the respiration-rate was 

 not noticeably different, the increased volume per respiration must be 

 due to the greater dead space with the mask. Assuming a dead space 

 of 100 c.c. for the subject with both methods of breathing, we find by 

 calculation that the dead space in the mask is about 40 to 70 c.c. 



The probability curves for the different factors in this comparison 

 have been plotted and are given in figure 51. The number of experi- 

 ments is somewhat too small for obtaining good curves, but they show 

 that in general the results with the mask are slightly more uniform than 

 with the nose-breathing. This is especially noticeable in the curves for 

 the oxygen consumption, the respiratory quotient, the total ventilation, 

 and the volume per respiration. 



All of the subjects were smooth- shaven, consequently no knowledge 

 was obtained as to the applicability of the mask for men having a 

 moustache or a beard. It is doubtful if the difficulties in making a 

 mask air-tight under these circumstances can be overcome. As far as 

 the measurement of the respiratory exchange is concerned, it is imma- 

 terial whether a mask or nosepieces are employed; but in using a mask, 

 one must know the dead space in the mask in order to obtain the true 

 ventilation during the experimental period. 



1 A new routine was established about this time in that records of the respiration-rate were 

 taken in the preliminary rest period. In this way the normal value for the respiration-rate could 

 be obtained for comparison with the values obtained during the experimental periods. 



