QUANTITY OF AIR BREATHED 



28 3 



The reserve air is that which may be expelled by a forcible and deeper 

 expiration, after an ordinary expiration, such as that which expels the tidal 

 air. The reserve air amounts to from 1,200 to 1,500 c.c. This is also termed 

 the supplemental air. 



The residual air is the quantity which still remains in the lungs after 

 the most violent expiratory effort. Its amount depends in great measure 



FIG. 235. Diagram of Hutchinson's Spirometer. (Landois.) .4, Graduated cylinder 

 serving as a receiver for the breath; it is supplied with a stopcock at the top for the ready 

 expulsion of air, and is balanced by weights passing over pulleys. B, Mouthpiece with 

 tube reaching nearly to the top of the graduated receiver (A} when the latter is sunk in the 

 reservoir ready for an experiment; there is a stopcock in this tube near the first angle, to 

 prevent regurgitation of air. C, Reservoir for the graduated receiver. In using the 

 spirometer the reservoir and graduated receiver are filled with water, or, to prevent the 

 absorption of carbon dioxide, with a saturated aqueous solution of common salt (NaCl). 

 When ready for an experiment, the stopcock at the top of the receiver is closed and that in 

 the tube of the mouthpiece opened, and the breath forced into the receiver. The receiver 

 rises as fast as the breath displaces the water. After the breath is forced into the receiver 

 the stopcock in the tube of the mouthpiece is closed, and the water outside and inside the 

 receiver brought to the same level, so that the air within the receiver shall be at the atmos- 

 pheric pressure. The amount of breath within the receiver is then read directly from the 

 scale attached to the receiver. For accurate measurement the breath should stand a few 

 minutes to acquire the temperature of the liquid over which it is collected; then the various 

 corrections for aqueous vapor tension, and the variations from the standard temperature 

 and pressure, should be made. 



on the absolute size of the chest, but may be estimated at about 1,000 c.c. 

 to 1,200 c.c. 



The total quantity of air which passes into and out of the lungs of an 

 adult, at rest, in 24 hours, is about 686,000 cubic inches. This quantity, 

 however, is largely increased by exertion; the average amount for a hard- 

 working laborer in the same time being 1,568,390 cubic inches. 



The Respiratory Capacity. The greatest respiratory capacity or vital 



