482 



ORGAN SYSTEMS OF MAN 



4500 

 c.c. 



5000. . 

 2500 ■ f 



1000 



forced « 

 expiration 1 5 



MENTAL WORK 



a 



1 1 1 1 



irfa^a 



-I minute- 



■l>i^ai^^aJI_^ak>^ 



Fig. 18-6. Breathing movements can be recorded by such a device as shown here. The movements alter the air 

 pressure in the rubber hose which is transmitted via the rubber tube to the rubber membrane which in turn 

 influences the movement of the lever, the tip of which Inscribes the magnified movements on the smoked drum. 

 With this instrument the tracings shown in A and B were made. See the text for an explanation of A. The 

 tracings in B are a result of mental work. A student was given a problem in mathematics to solve which required 

 one minute. How his breathing was influenced during this mental work is shown in the tracing. 



air at the end of a quiet inspiration and can 

 force out a great deal more air at the 

 end of a quiet expiration. These facts indi- 

 cate that the lungs have a great deal more 

 capacity than is used in non-strenuous 

 work. This constitutes a reserve that is 

 always available when needed. 



In quiet breathing, about 500 cc. of air 

 is breathed in and out. This is known as 

 tidal air, reminiscent of the tides (Fig. 

 18-6). Upon forced inspiration, 1500 cc. 



more can be taken into the lungs. This is 

 known as complemental air. Forced ex- 

 piration can deliver about 1500 cc. of 

 air, known as supplemental air. Therefore, 

 complemental air together with tidal and 

 supplemental air amounts to about 3500 cc, 

 the total capacity that can be taken in and 

 forced out under conditions of heavy exer- 

 tion. This amount is called vital capacity. 

 There is some variation in this quantity, de- 

 pending on the size, age, sex, and training 



