594 Anatomy, Physiology, and Pathology of the 



around each terminal bronchus, somewhat after the manner 

 of grapes upon their stalk (fig. 17) ; and " it has been calcu- 

 lated by M. Rochaux, that in the human subject about 18,000 

 surround each bronchus, and that the total number in the 

 lungs amounts to six hundred millions.''' " If this estimate," 

 says Dr. Carpenter, " be even a remote approximation to the 

 truth, it is evident that the amount of surface exposed by the 

 walls of those minute cavities must be many times greater than 

 that of the exterior of the body." * The 

 air-cells follow no definite shape : they 

 are for the most part flattened against 

 each other, and are said to vary in size in 

 the human subject from about the '200th 

 to the 70th of an inch. In the ox the air 

 cells are many times smaller than in man, 

 and even more minute than those of the 

 horse ; and injected preparations of their ca- 

 pillaries show that the rete formed by these 

 vessels is likewise finer, or more closely 

 woven. This circumstance throws some 

 light on the peculiar appearances met with 

 in pleuro-pneumonia, and will hereafter be 



alluded to. ^ ^ ^^ Terminal bronchus, commu- 



From the foreo^oin^ remarks it is ap- nicating with r, the air-ceiis. 



1 1 1 • r I n r xi i • ^''^ P^"^*^^ *^^ highly mag- 



parent that the chief bulk ol the iungs is nitied. 

 made up of air-cells, surrounded by their 



network of vessels, and communicating with the minute ramifica- 

 tions of the bronchial tubes. Through the medium of these 

 structures both elastic and contractile tissue enter into the com- 

 position of the lungs, by which they possess a certain amount of 

 action independent of the expansion and contraction of the boun- 

 daries of the chest, and are thus enabled of themselves to assist in 

 the process of respiration. The various structures forming the 

 lungs are united together by areolar tissue, and they are also col- 

 lected into small masses, termed lobules, which are joined to each 

 other by the same material. Hence the expressions interstitial 

 and interlobular areolar tissue : the former being applied to the 

 bond of union between the different structures, and the latter to 

 that connecting the lobules to each other. In the ox the lobules 

 are very distinct, and the amount of areolar tissue is proportion- 

 ably large (see fig. 19) ; thus again accounting for the appear- 

 ances produced by pleuro-pneumonia. 



Each lung is divided into lobes by a deep fissure : — the num- 

 ber of these lobes varies, although not to great extent, in different 

 classes of animals. In the ox and sheep, the right lung consists 

 of four, and the left of three lobes. The lungs are held in their 



* Manual of Physiology, p. 389. 



