BY H. S. HALCRO WARDLAW. 547 



with the bag. The expiration is made at the end of a normal inspiration. The 

 subject then breathes normally for about 5 minutes to allow any respiratoi-y and 

 circulatory disturbances' caused by the deep expiration to subside. He then ex- 

 pires as deeply as possible into the air, and takes a deep inspiration from the 

 bag containing his expired air. This inspiration he holds in his lungs for 5-10 

 seconds, then expires into the bag again, as deeply as possible, immediately clos- 

 ing it as before. The subject then breathes normally for about 5 minutes again, 

 empties his lungs, and takes another deep inspiration from the bag. He holds 

 the inspiration for another 5-10 seconds and expels it into the bag, and closes 

 the bag as before. This procedure may be repeated almost indefinitely without 

 inconvenience. With each succeeding inspiration from the bag the subject takes 

 into his lungs air which he has already held in his lungs for a period increasing 

 with the number of expii'ations into the bag. 



A limitation of the method is the fact that it is impossible to empty the 

 lungs to exactly the same extent before each inspiration from the bag. Each 

 inspiration is, therefore, mixed with a variable amount of residual air, and the 

 regularity of the figures obtained is thus somewhat impaired. As will be seen 

 from the accompanying Tables, however, the figures give a clear answer to the 

 question which the experiments were carried out to settle: namely, whether the 

 levels of the carbon dioxide content to which the composition of the alveolar air 

 seemed to be tending according to the experiments of the author's previous 

 paper, have any real existence or not. 



Results. 

 Carbon dioxide. 



In the following Table are shown the variations of the carbon dioxide eon- 

 tent of the alveolar air as successive inspirations, made from a bag as described, 

 are held in the lungs under normal pressure. The initial inspiration of each 

 experiment was made from the atmosphere. 



Table 1.* 



Alveolar carbon dioxide content after holding expired air in lungs under 

 negative pressure. Initial inspiration from atmosphere. 















Number of 

 inspiration 















Expt 



1 



1 Expt 



2 



Expt 



3 



Percent. 



Tension 



1 Percent. 



Tension 



Percent. Tension 



1 



5.20 



37.5 



5.10 



37.0 



5.17 



37.1 



2 



5.83 



42.0 



6. 30 



45.7 



6.41 



46.0 



3 



6.34 



45.7 



6.54 



47.4 



6.S4 



49.1 



4 



6.42 



46.3 



6.95 



50.4 



7.05 



50.3 



5 



6.54 



47.2 



6.94 



50.3 



6.99 



50.2 



6 



6.58 



47.4 



6.93 



50.2 



6.90 



49.5 



The above fig-ures show that during the last three inspirations the alveolar 

 carbon dioxide content had reached approximate constancy in each experiment. 

 The mean figures for the period of constancy are 6 . 81 % or 49 . 1 mm. Hg., values 

 which lie within 0.12 % or 0.7 mm. Hg. of those apjoroached in the previous 

 experiments. 



In the next Table the variations of alveolar carbon dioxide are shown during 

 experiments similar to those in Table 1, except that the initial inspirations were 



* The percentages in the tables are by volume of the dry alveolar air. The ten- 

 sions are in mm. of Hg and are also calculated for the dry alveolar air. 



