158 DISEASES OF THE LUNGS. 



Delafond's account is the best veterinary one, although 

 he has confounded dilatation of the air-conduits with the ex- 

 travasation of air. We shall transcribe it : — 



The AIR-CELLS are little transparent vesicles or culs-de- 

 sac, having partitions of dense cellular tissue, by which they 

 are united into small masses or lobules, rendered distinct 

 by the looser cellular tissue which surrounds them, and 

 connects them with other lobules. In domestic animals 

 the form and number of the air-cells vary, not only with 

 the species, but in individuals of the same kind, according to 

 the age and to the part of the lung they occupy. In young 

 horses and in foals they are small, and closely grouped to- 

 gether, which gives gravity to the lung, and at the same time 

 elasticity ; but with age they become dilated, atrophied, and 

 and in part destroyed, which renders the lung lighter, less 

 elastic, softer, and of a paler colour. The air-cells are more 

 numerous in the centre of the lung than at the extremities; 

 but are most capacious and at greatest interval within the 

 anterior lobes. This distribution explains why the respira- 

 tory murmur is more audible in the middle of the lung. 



Enlargement of the air-cell has been observed to the 

 extent or more of a pea. But the cells are very rarely found 

 enlarged in every part of the lung : the anterior lobes, and 

 borders, and mediastinal portion of the right lung, fre- 

 quently exhibit them ; and in the middle of the sound lung 

 are here and there found dilated air-cells ; and often these 

 two latter conditions are combined. When the dilatation of the 

 cells is generalj the lungs, on opening the thorax, appear as 

 if they had been inflated. The atmospheric pressure col- 

 lapses them only to about one third or one fourth of their 

 volume. They are of a pale rose-colour, elastic, and ex- 

 tremely light; and more buoyant in water than sound 

 lungs. In general, their cells have acquired the volume of 

 a millet or hemp seed, and particularly in the anterior 

 lobes, and along the posterior and inferior borders of the 

 lungs. The parenchyma, on being cut, collapses only to 

 the extent of the incision; and there is no effecting a 

 perfect collapse of it without incising it in every direction. 



