RESPIRATORY VOLUMES. 



20 5 



with perforation of an intercostal space Aron found the elastic tension to be from 

 4.5 to 6.8 mm. If, however, the thorax is, by force applied from the outside, 

 brought into the expanded position assumed during inspiration, the elastic trac- 

 tion will be increased to 30 mm. 



If the glottis be closed during inspiratory dilatation of the thorax, 

 the elastic lungs also will expand, and there will be produced a rarefac- 

 tion of the air within the lungs, as this air must expand to a greater 

 volume. If the glottis is now suddenly opened, the atmospheric air 

 will enter the lungs, until the density of the air within equals that of 

 the atmosphere. On the other hand, if the chest and the lungs be com- 

 pressed by expiratory efforts, with a closed glottis, the air in the lungs 

 will become denser, that is, compressed into a smaller volume. If the 

 glottis now be opened, air will escape from the lungs, until the internal 

 and external pressures are equalized. As the glottis is open during 

 ordinary respiration, the adjustment of the diminished or increased 

 air-pressure during inspiration and expiration will occur gradually. It 

 is certain, however, that there exists in the air within the lungs a slight 

 negative pressure during inspiration and a slight positive pressure 

 during expiration. This may be measured in the trachea of persons 

 having wounds of this tube, and equals i mm. during inspiration and 

 from 2 to 3 mm. during expiration. According to J. R. Ewald the 

 total figures are only o.i mm. and 0.13 mm. respectively. 



The so-called abdominal pressure within the abdomen is generally 

 increased during expiration, and declines during inspiration in man and 

 in dogs, while in rabbits it is increased during inspiration. Moderate 

 increase of the abdominal pressure increases somewhat the arterial 

 blood-pressure, as well as the action of the heart; more pronounced 

 increase of abdominal pressure diminishes both. 



RESPIRATORY VOLUMES. 



The lungs never completely empty themselves of air. Therefore, in 

 filling and emptying the lungs during inspiration and expiration, only 

 a part of the contained air is subjected to change, the amount depending 

 on the depth of the respirations. 



Hutchinson in this connection established the following distinctions : 



i. Residual air is the volume of air that remains in the lungs after 



complete expiration. This can be estimated approximately after death 



by collecting over water the air from the lungs after ligating the trachea. 



H. Davy and Grehant estimated the amount during life in the following man- 

 ner: The subject makes a forcible expiration, and then breathes for a while from 

 and into a spirometer, filled with a measured quantity of hydrogen. If it can be 

 assumed that the residual air has been completely admixed with the hydrogen, 

 the percentage of air in the spirometer after forced expiration will indicate the 

 quantity of residual air. The observers named found the amount to be from 1200 

 to 1700 cu. cm. Berenstein, by a similar method, estimated the residual air to 

 be equal to from one-fifth to one-fourth of the vital capacity. 



The following wholly different method has also been employed to determine 

 the residual air: The amount of an unknown volume of air x can be calculated 

 from the increase in volume that it undergoes when the pressure upon it is lessened, 

 for this increase in volume is directly proportional to the quantity of gas, and 

 to the diminution in the pressure upon it. If Pj is the original pressure to which 

 the gas is exposed, P 2 the other, lessened pressure, and d the measurable increase 

 in volume of x, then 



x = (P 2 Xd) : (P! P 2 ). 



For carrying out this experiment Pfltiger constructed his pneumometer. The sub- 



