FREQUENCY AND CHARACTER OF RESPIRATORY MOVEMENTS 481 



of the small bronchial tubules have come together before the in- 

 fundibula have been completely emptied. In this way a portion 

 of the residual air has been entrapped in the different air cells. This 

 constitutes the minimal air. It is possible to remove it, however by 

 chemical means ; for example, by displacing it with oxygen and carbon 

 dioxid and bringing it in contact with water. A lung so treated ceases 

 to float. 



From the foregoing discussion it may readily be gathered that the 

 reserve amount of air which is contained in the lungs at the end of a 

 quiet expiration, following a quiet inspiration, amounts to about 

 2500 c.c. and consists of the residual and supplemental portions. 

 It is designated as the stationary air. The term vital or respiratory 

 capacity signifies the quantity of air which may be expelled from the 

 lungs by the most forcible expiration after the deepest possible in- 

 spiration. It includes the tidal, complemental and supplemental por- 

 tions and may, therefore, be estimated at 3700 to 4000 c.c. If to this 

 quantity is added the residual air, the lung capacity is obtained, which 

 in round numbers may be said to equal 5000 c.c. The term bronchial 

 capacity refers to the quantity of air which is accommodated in the 

 trachea and bronchi. It is generally estimated at 140 c.c. so that only 

 360 c.c. of the 500 c.c. of tidal air are actually forced into the deeper 

 passages of the lungs. ^ What bearing this fact possesses upon the 

 interchange of the gases will be seen later. While it is true that these 

 figures allow us to draw definite conclusions regarding the respiratory 

 power of an individual, no special clinical value can be attached to 

 them, because they may be materially increased by practice and are 

 subject to a number of conditions, such as posture, age, sex, race, 

 and occupation. Mountaineers, for example, possess a greater 

 respiratory capacity than the inhabitants of lowlands. 



These data now permit us to compute the quantity of air respired 

 by an adult person during a given period of time. Assuming that the 

 respiratory frequency is 15 in a minute and that the tidal air amounts 

 to 500 c.c, then 7.5 liters are breathed in a minute, 450 liters in an 

 hour, and more than 10,000 liters in the course of a day. It is from 

 this enormous quantity of air that the oxygen requirement of our 

 tissues is satisfied. 



Modified Respiratory Movements.— The rhythmical enlargement 

 of the thorax has as its object the ventilation of the lungs so that a 

 proper interchange of the gases may be had between the intrapulmonic 

 air and the blood. Under certain conditions, however, the respiratory- 

 current of air is employed during brief periods of time for other pur- 

 poses, this change generally necessitating a modification of either 

 the inspiratory or expiratory movement. Acts of this kind are speaking, 

 singing, coughing, sneezing, sighing, laughing, crying, sobbing, hic- 

 cough, yawning, and snoring; in fact, if other species of animals are 

 here taken into consideration, this list may be made to include a 



1 Loewy, Pfliiger's Archiv, Iviii, 1894, 416. 

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