PHYSIOLOGY OF MOUTH-BREATHING APPLIANCES. 187 



through the mouthpiece for approximately 15 minutes before the period 

 began and from 10 to 15 seconds for the other periods, the procedure 

 being similar to that in the standing tests. In these experiments the 

 oxygen consumption was large and hence the respiration-rate and 

 pulmonary ventilation were correspondingly large. The error in the 

 technique would consequently play a much smaller role than in the 

 standing experiments. Table 51 gives the respiration and ventilation 

 rates on these days measured in minute or quarter-minute intervals for 

 the first 5 to 7 minutes of the period. 1 The method of presentation of 

 results is the same as in table 50. 



The results show that the respiration-rate underwent no pronounced 

 change in one direction or the other in those periods in which the sub- 

 ject had been breathing through the mouthpiece for 15 minutes and in 

 which the measurements were made on the per minute basis. There 

 was a slight tendency for the rate to be usually a little lower than with 

 the short preliminary use of the mouthpiece. In the quarter-minute 

 measurements there was more variation, which was sufficiently small 

 to be ascribable to the error in estimation for such short periods as 

 one-quarter minute, and this variation was not so uniform as to indi- 

 cate that the mouthpiece had more than a temporary effect. It would 

 appear, therefore, that the practice in our experiments of inserting 

 the mouthpiece 2 minutes before the period began probably gave 

 ample time for the respiration-rate to become settled, even under 

 conditions requiring a great increase in the rate of respiration. 



The pulmonary ventilation in the grade-walking experiments varied 

 considerably from minute to minute. The volumes per minute were 

 usually larger in those periods in which the mouthpiece had just been 

 inserted than in the periods in which it had been used for 15 minutes or 

 more, but this difference tends to become smaller as the experiment pro- 

 gressed. It may also be noted that the ventilation for these periods 

 was frequently larger in the first and second quarter-minutes than in 

 the next following, indicating a rather rapid adjustment to the dis- 

 turbance of the mouthpiece at the beginning of the period. 



From the data in table 51, which usually represent only 5 or 6 min- 

 utes of an 8 to 11 minute period, the general impression is obtained 

 that in the majority of periods the unreduced pulmonary ventilation 

 was somewhat higher in those tests with a short period of preliminary 

 mouthpiece breathing. This impression is confirmed by the average 

 values of the reduced ventilation for the whole of each period given 

 in table 16 (p. 78) for the several dates. Bearing in mind that the 

 comparison periods were alternate, and that the first measurement 

 on each day was preceded by a long period of mouthpiece breathing, 

 it is seen that the pulmonary ventilation was in all but two sets of com- 

 parisons (that of March 7 and the last pair of March 8) larger in the 

 period with the short preliminary mouthpiece breathing. Averaging 



1 The quarter-minute records were computed to the full-minute basis. 



