62 



THE LUNGS, BY FRANZ EILHARD SCHULZE. 



animals ; whilst they no longer lie on the same plane, but fre- 

 quently running through the septal wall project sometimes into 

 one and sometimes into the other of two contiguous alveoli. 



If the course of the capillaries be followed in transverse 

 sections of such alveolar septa, they will be seen to form loops, 

 projecting now on this, and now on that side. These appear 



Fig. 131. 



Fig. 131. Section of the alveolar parenchyma of human lung, in- 

 jected from the pulmonary artery, a a, Free margins of the alveoli ; 

 6, small artery ; c c, vertical walls of alveoli divided transversely. 



most tortuous when the vessels are very fully injected and the 

 alveoli are not much distended ; whilst with full dilatation of 

 the alveoli they lie more closely applied to the walls, though 

 the greater part of their circumference even then projects 

 freely into the interior of the alveolus. That these free sur- 

 faces of the capillaries are, in many parts at least, destitute of 

 an independent investment of connective tissue, can be most 

 easily demonstrated in the loops running round the free borders 

 of the alveolar septa. The diameter of the capillaries does not 

 materially vary with the size of the animal, but amounts in 



