34 



COMPARISONS OF RESPIRATORY EXCHANGE. 



dioxide by passing air 2 or 3 minutes through the barium-hydroxide 

 container, as previously described. After the experimental period is 

 over, the ventilation is stopped and oxygen is admitted until the 

 pressure is the same as at the beginning of the experiment. The 

 carbon-dioxide absorbers are then disconnected and weighed, and the 

 oxygen cylinder is also weighed. The loss in weight of the oxygen 

 cylinder and the gain in weight of the carbon-dioxide absorber and 

 accompanying water-absorber give respectively the quantities of oxygen 

 consumed and carbon dioxide exhaled. 



SPIROMETER UNIT. 



The spirometer unit was developed in the winter of 1911-12, and a 

 description of it was published at that time. 1 Subsequently a number 

 of modifications were made in the apparatus; it is accordingly desi- 

 rable to give a complete description in English of the apparatus in 

 its present form. 



General Plan of Apparatus. 



The general principle of the spirometer type of the universal respi- 

 ration apparatus is the same as that of the tension-equalizer type. 

 The subject breathes into a closed volume of air which is kept in motion 

 by a rotary blower. The water-vapor and carbon dioxide of the 

 expired air are removed by 



suitable absorbers and oxy- spiromete* 



gen is admitted to the appa- 

 ratus. The volume of the 

 system must be the same at 

 the beginning and end or its 

 changes known. A spiro- 

 meter bell, suspended in oil 

 or water, is substituted for 

 the tension equalizer, the 

 vertical movements of the 

 bell giving quantitatively 

 the volume alterations of the 

 respiratory tract. A device 

 is included for adding the in- 

 spiratory volumes and some 

 mechanical changes to assist 

 in manipulation and opera- 

 tion have also been made. 



The general scheme of the apparatus may be seen in figure 9. 

 After the air leaves the rotary blower, it passes first through a water- 

 absorber, next through a carbon-dioxide absorber, and then through 

 the spirometer, returning from there to the pump or rotary blower. 



Lungs 



-&%-£) 



c 



J 



Pump 



Absorbed 



H 2 

 Absorbed 



Fig. 9. — Schematic outline of ventilation system 

 of spirometer unit. 



Benedict, Deutsch. Archiv f. klin. Med., 1912, 107, p. 156. 



