206 COMPARISONS OF RESPIRATORY EXCHANGE. 



results with the Mueller valves. This is particularly true with subjects 

 who have been trained in the use of the valves. This was shown by 

 the fact that much more satisfactory results were obtained with W. J.T. 

 and J. J. G. in the second series of experiments after they had become 

 accustomed to the valves in the first series of experiments. 



BENEDICT RESPIRATION APPARATUS (SPIROMETER UNIT) WITH AND WITHOUT 



ADDITIONAL DEAD SPACE. 



In all apparatus employed for the determination of the respiratory 

 exchange, when the subject is not inside a chamber, there is a volume of 

 dead air which must be swept out at each respiration before fresh air 

 can reach the respiratory tract of the subject. When inspiratory and 

 expiratory valves are used, generally that part of the connecting 

 tee-piece which is nearest the subject is filled with expired air at each 

 expiration , and this must be replaced by fresh air. In a closed-circuit 

 apparatus without valves there is likewise a dead space between the 

 respiratory tract of the subject and the moving current of air inside the 

 apparatus. The only exception to this rule is when a person inhales 

 through the mouth and exhales through the nose, or vice versa. 



In the construction and arrangement of all respiration apparatus, 

 the attempt is always made to reduce the dead space as much as pos- 

 sible, for it has been assumed that marked increase in the dead space 

 would result in such a disturbance in the respiratory exchange that the 

 results would not represent the true values. 



While in the construction of the Benedict universal respiration appa- 

 ratus every effort was made to minimize the dead space between the 

 subject and the moving current of air, in some of the experiments 

 with H. F. T. it became necessary to lengthen it in order that he might 

 lie on his side. 



The effect of thus varying the dead space between the subject and 

 the moving current of air was accordingly studied with the spirometer 

 unit in a considerable number of experiments. In this study the respi- 

 ratory exchange with the normal dead space was compared with the 

 results obtained when the dead space was arbitrarily increased by 

 inserting a piece of rubber tubing of about 20 mm. internal diameter 

 between the three-way valve and the nosepieces or mouthpiece, varying 

 the length of the rubber tubing as desired. The experiments were 

 made in four series, the increase in the dead space being 45, 90, 135, 

 and 224 c.c. respectively. There was usually a 5-minute preliminary 

 period of breathing through the nosepieces before the experimental 

 period itself began. 



The pulse-rate was recorded by means of the Bowles stethoscope; 

 a graphic record of the respiration was obtained from the movements 

 of the spirometer bell, and in many of the experiments an additional 

 record was obtained with the chest pneumograph. In practically all of 

 the experiments a record of the muscular activity was secured by a 



