304 PULMONARY MUCOUS TISSUE. 



physical conditions of the gaseous exchanges, and thus forms, 

 as it were, a measure of our life, since to breathe is to live : a 

 large number of instruments have been constructed for the 



Fig. 79. Circulation through the lung.* 



purpose of estimating this amount ; of these, the best known is 

 Hutchinson's spirometer. 1 It consists simply of a gasometer 



1 Hutchinson, " Medico-chirurg. Transactions," 1846. More 

 recently, the anapnoyrapher of Messrs. Bcrgeon and Kastus (de 

 Lyon) has been employed for comparative estimation. This instru- 

 ment is, briefly, Marey's sphygmograph, applied to currents of air 

 which enter the chest or leave it at each respiration; it consists, 

 chiefly, of a spring applied to the inspiratory and the expiratory 

 current. A registering lever, furnished with a writing point, 

 grows broader at the opposite end, and to this broader part a tube, 

 into which the person breathes, is closely fitted. This part, which 

 js an extremely light and delicate plate of aluminium, serves as a 

 valve, kept immovable and vertical by two opposite springs of equal 

 force, but moving with each respiratory current, and drawing after 

 it the writing lever, which traces on the paper, first by vertical and 



* a, b, Right heart (venous blood). /,/, Left heart (arterial blood), c, Pul- 

 monary artery and its branches (carrying the venous Mood into the lung). 

 , Pulmonary veins (rarely containing arterial blood), d, Vascular network of 

 the lung, h, Aorta. ( Dal ton, "Human Physiology.") 



