206 



RESPIRATORY VOLUMES. 



ject is placed in a large, hermetically sealed chamber (human cabinet) , in which 

 at first the pressure equals that of the atmosphere (P^. The contained air is 

 then rarefied by means of a pump, until the pressure P 2 is obtained, as indicated 

 by a manometer inserted in the chamber. In this process a part of the residual 

 air (x) will naturally escape during quiet expiration. This is collected and meas- 

 ured (d) by means of a spirometer connected in an air-tight manner with the 

 air-passages. In this way Pfliiger found x to be from 400 to 800 cu. cm. Gad, 

 working with different apparatus based on the same principle, estimates the residual 

 air to be half the vital capacity; Schenck gives the proportion of the former to 

 the latter as i to 3.7. 



2. Reserve air is the additional volume of air that can be forced out 

 after a quiet expiration. It measures from 1248 to 1804 cu. cm. 



The procedure of H. Davy and Grehant may also be applied to the estimation 

 of reserve air. 



3 . Respiratory or .tidal air is the volume of air that is taken in and 

 given off during quiet respiration. In adults under normal conditions it 



amounts to about 507 cu. cm. between 

 367 and 699 cu. cm., according to Vier- 

 ordt; in the new-born about one-quar- 

 ter of this amount. 



4. C omplemental air is the term ap- 

 plied by Hutchinson to the additional 

 volume of air that may be taken in 

 during a forced inspiration immediately 

 succeeding a quiet one. 



5. Vital capacity indicates the vol- 

 ume of air that escapes from the lungs 

 between the highest phase of inspiration 

 and the lowest phase of expiration. 

 For Germans it amounts to 3222 cu. 

 cm. on an average, and for Englishmen 

 to 3772 cu. cm. 



From the foregoing it follows that 

 after a quiet inspiration both lungs 

 contain about from 3000 to 3900 cu. cm. 

 of air ( i -f 2 -f- 3 ) ; after a quiet expi- 

 ration from 2500 to 3400 cu. cm. (i -f- 

 2). From this, as from 3, it follows 

 that during quiet respiration only about 

 one-sixth or one-seventh of the air in the lungs is changed. 



If, during a series of quiet respirations, a solitary inhalation of hydrogen be 

 made, and if the expired air be examined to determine how long the hydrogen 

 may be detected in it, it will likewise be found that the air in the lungs com- 

 pletely renews itself (becomes free of hydrogen) in from 6 to 10 respirations. 



Donders estimates that the combined bronchial tree and trachea contain about 

 500 cu. cm. of air. 



The vital capacity is determined by means of Hutchinson 's spirometer (Fig. 

 76). The determination is of importance in persons suffering from disease of the 

 thoracic organs. The vital capacity may be influenced by consolidation, destruc- 

 tion, or emphysema of the pulmonary tissue; by the presence of fluids, blood, air, 

 or new-growths in the thoracic cavity; by diminished mobility of the chest; by 

 weakness of the respiratory muscles ; by enlargement of the heart or pericardium ; 

 or by distention of the abdomen. 



By means of a large tube provided with a mouth-piece, the subject (holding his 

 nostrils closed) blows his expiratory air into a graduated gasometer bell- jar that 

 is suspended over water and evenly balanced by a system of weights rand pulleys. 



FIG. 76. Hutchinson's Spirometer. 



