112 RESPIRATION 



4. Complemental Air ; the excess over the ordinary breathing air, 

 which may be introduced by a forcible inspiration. 



In measuring the air changed in ordinary breathing, it has been found 

 that the acts of respiration are so easily influenced and it is so difficult 

 to experiment on any individual without his knowledge, that the results 

 of many good observers are not entirely reliable. This is one of the 

 most important of the questions under consideration. The difficulties in 

 the way of estimating with accuracy the residual, reserve or complemen- 

 tal volumes, will readily suggest themselves. The observations on these 

 points which may be taken as the most definite and exact are those of 

 Herbst and of Hutchinson. Those of the last-named observer are very 

 elaborate and were made on a large number of subjects of both sexes 

 and of all ages and occupations. They are commonly accepted by 

 physiologists as the most extended and accurate. 



Residual Air. Perhaps there is not one of the questions under con- 

 sideration more difficult to answer definitely than that of the quantity of 

 air remaining in the lungs after a forced expiration ; but it fortunately is 

 not one o great practical importance. The residual air remains in the 

 lungs as a physical necessity. The lungs in health are always in contact 

 with the walls of the thorax ; and when the chest is reduced to its small- 

 est dimensions, it is impossible that more air should be expelled. The 

 volume which thus remains has been variously estimated. The residual 

 volume has been put at about one hundred cubic inches (1639 cubic 

 centimeters), but the quantity varies very considerably in different indi- 

 viduals (Hutchinson). Taking everything into consideration, it may be 

 assumed that this estimate is as nearly correct as any. 



Reserve Air. This name is given to the volume of air that may be 

 expelled and changed by a voluntary effort, but which remains in the 

 lungs, added to the residual air, after an ordinary act of expiration. It 

 may be estimated, without reference to the residual air, by forcibly ex- 

 pelling air from the lungs after an ordinary expiration. The average 

 volume, according to Hutchinson, is one hundred cubic inches (1639 

 cubic centimeters). 



More or less of the reserve air is changed whenever there is a neces- 

 sity for more complete renovation of the contents of the lungs than 

 ordinary. It is encroached upon in the unusually profound inspiration 

 and expiration which occur once in every five to eight acts. It is used in 

 certain prolonged vocal efforts, in blowing etc. Added to the residual air, 

 it constitutes the minimum capacity of the lungs in ordinary respiration. 

 As it is continually receiving .watery vapor and carbon dioxide, it is 

 always more or less vitiated, and when reenforced by the breathing air, 

 which enters with inspiration, is continually in circulation, in obedience 



