o-/ 
THE RESPIRATORY SYSTEM. 367 
Respiration may, then, be regarded from a physical and 
chemical point of view, though in this as in other instances we 
Fig. 297.—Trachea and branchial tubes (Sappey). 1, 2, larynx ; 3, 3, trachea; 4, bifurcation 
of trachea ; 5, right bronchus; 6, left bronchus; 7, bronchial division to upper lobe of 
right lung ; 8. division to middle lobe ; 9, division to lower lobe ; 10, division to upper lobe 
of left lung ; 11, division to lower lobe ; 12, 12, 12, 12, ultimate ramifications of bronchia ; 
18, 18, 13, 18, lungs, represented in contour ; 14, 14, summit of lungs ; 15, 15, base of lungs. 
must be on our guard against regarding physiological processes 
as ever purely physical or purely chemical. The respiratory 
process in the mammal, unlike the frog, consists of an active 
and a (largely) passive phase. The air is not pumped into the 
lungs, but sucked in. So great is the complexity of the lungs 
in the mammal, that the frog’s lung (which may be readily 
understood by blowing it up by inserting a small pipe in the 
glottic opening of the animal and then ligaturing the distended 
organ) may be compared to a single infundibulum of the mam- 
malian lung. 
Assuming that the student is somewhat conversant’ with the 
