4IO TEXT-BOOK OF PHYSIOLOGY 



the beginning of the inspiration. The time relations of the two movements 

 can be obtained by a magnet-signal actuated by an electric current inter- 

 rupted once a second. The ratio of inspiration to expiration has been 

 represented as 5 to 6, or 6 to 8. 



Volumes of Air Breathed. The volumes of air which enter and leave 

 the lungs with each inspiration and expiration naturally vary with the ex- 

 tent of the movement, though four volumes at least, may be determined: 

 (i) that of an ordinary inspiration; (2) that 

 of an ordinary expiration; (3) that of a forced 

 inspiration; (4) that of a forced expiration. 



The apparatus employed for the determina- 

 tion of these different volumes is the spirometer, 

 a modification of the gasometer. The form 

 introduced by Jonathan Hutchinson, of which 

 Fig. 191 is a modification, consists of two 

 metallic cylinders, one containing water, the 

 other containing air, the latter being inserted 

 into the former. The air cylinder is balanced 

 by a weight so accurately that it remains 

 stationary in any position. A tube, penetrating 



rNSR 



FI G ' 190. A PNEUMATOGRAM. (After Marey.} 



FIG. 191. A SPIROMETER. 

 (Boruttau.) 



the base of the water cylinder, is continued upward through and above the 

 level of the water. The air-space above is thus placed in free communica- 

 tion with the atmospheric air. A stopcock at the outer end of this tube 

 prevents the escape of the air when this is not desirable. To the free end of 

 the tube a rubber tube provided with a suitable mouthpiece is attached, 

 through which air can be breathed into or out of the air cylinder. With 

 each inspiration the air cylinder descends; with each expiration it ascends. 

 A scale, on the side support, graduated in cubic inches or centimeters, in- 

 dicates the volume of air inspired or expired. 



With an apparatus of this character Hutchinson, from a long series of 

 observations, defined and determined the above-mentioned four volumes as 

 follows : 



i and 2. The tidal volumes, which flow into and out of the lungs with each 

 . inspiration and expiration, which vary from 20 to 30 cubic inches (330 

 to 500 c.c.). 



3. The reserve or supplemental volume, that which flows out of the lungs, 



in addition to the tidal volume, as a result of a forcible expiration, 

 and which amounts to about 100 cubic inches (1650 c.c.). 



4. The complemental volume, that which flows into the lungs, in addition to 



the tidal volume, as a result of a, forcible inspiration, and which amounts 

 to about no cubic inches (1800 c.c.). 



