162 COMPARISONS OF RESPIRATORY EXCHANGE. 



would hold only about 25 to 30 liters without noticeable pressure. 

 The periods in which the bag was used were only about 5 minutes in 

 length, with a preliminary period of 10 minutes. 



This bag was used up to and including July 3, 1912, when another 

 bag was secured of rubber-covered cloth which was of the same dimen- 

 sions as the larger bag described by Douglas. The possibility of the 

 diffusion of carbon dioxide through the rubber cloth was tested by 

 partly filling the bag with expired air and taking samples from time 

 to time. No appreciable change in the carbon-dioxide content was 

 found in the length of time which would elapse between the beginning 

 of a period and the time of taking the sample. This bag was used for 

 the remainder of the series, the duration of the periods being 10 min- 

 utes, with a preliminary period of 5 minutes. 



Several types of valves were employed in this comparison. In all 

 of the experiments with the first bag and also in a part of the experi- 

 ments with the larger bag, the rubber-flap valves described on page 69 

 were used. In some of the later experiments use was also made of 

 both the mica-flap valves ordinarily employed with the Douglas method 

 and the Tissot valves. 



The routine was the same as in the other comparisons, except that 

 in a number of the experiments the subject occupied a reclining chair, 

 this position being more convenient with the Douglas method. Both 

 the mouthpiece and the nosepieces were used as noted in the statistics. 

 As in other comparisons, the pulse-rate was determined by the Bowles 

 stethoscope. The respiration was recorded from the chest pneumo- 

 graph in the periods with the Douglas apparatus and from the move- 

 ments of the spirometer bell in the periods with the spirometer unit. 

 The degree of muscular repose was determined in nearly all of the 

 experiments with the spirometer unit by means of the lever bed-spring 

 arrangement, 1 the only exception being the first experiment with 

 E . W. H. This device was also used in many of the experiments with the 

 Douglas method, but in some of the experiments the only indications 

 of the quietness of the subject were obtained from the records of the 

 chest pneumograph. None of the subjects were familiar with the 

 Douglas apparatus, but, with the exception of M. J. S., they had all 

 had previous experience with the spirometer unit. The statistics of 

 the 16 experiments in this comparison are given in the following pages. 

 My thanks are due to Mr. L. E. Emmes for assistance in carrying out 

 a considerable number of the experiments. 



STATISTICS OF EXPERIMENTS. 



E. W. H., June 21, 1912. Spirometer unit, 3 periods; Douglas apparatus, 

 2 periods; apparatus alternated. Pneumatic nosepieces with both apparatus; 

 rubber-flap valves and small bag with Douglas apparatus. Subject sat in 

 reclining chair; was very difficult to work with, owing to his restlessness and 



1 See p. 84. 



