306 



PULMONARY MUCOUS TISSUE. 



SSoo 



M 



JOOO 



In order to ascertain exactly the capacity of the lungs, and 

 the quantity of air introduced into them, the different por- 

 tions of which this air is 

 successively composed must 

 be demonstrated : that por- 

 tion of the air which cannot 

 be driven out of the lungs 

 by the most forcible expira- 

 tion is called residual air 

 (a) ; the air which may still 

 be expelled after an ordinary 

 expiration (though showing 

 the difference between a 

 moderate and a forced ex- 

 piration) is called air in 

 reserve (b) ; the air which 

 we inhale and exhale at each 

 ordinary respiration is called 

 the respiratory air (c) ; fin- 

 ally,that quantity of air which 

 we can inhale by means of a 

 forcible inspiration (or the 

 difference between normal 

 and forced inspiration) is 

 called complementary air 

 (Hermann). 



These names being accept- 

 ed, nothing is easier than to 

 estimate the last quantity (d) 

 experimentally: the numeri- 

 cal value of the complement- 

 ary air varies essentially with 

 individuals, the diversity ap- 

 pearing to depend less on 

 the size of the individual, 

 than on the conformation of 

 the chest. The quantity increases with the increase of the 

 transverse diameter of the cavity of the thorax. The three 

 diameters of the lung, or, what is the same thing, of the 



* V, Brass cylinder. TT, Respiratory tube. A, Mouth of the respiratory 

 tube. C, Receiver or gasometer. P, Balance-weight. S, Chain. R, Pulley. 

 L, Scale, M, Upright bar. G, Case, supporting the scale. N, Surface of the 

 fluid contained in the reservoir. E, Bottom of the gasometer. O, Open mouth 

 of the gasometer. 



T 



iij. 80. Schnepf's Spirometer.* 



