SECT. J 76.] BRONCHIAL TUBES AND AIR-CELLS. 383 



may most readily convince ourselves of this arrangement, by making 

 sections in different directions of an inflated and dried lung, or by 

 examining a preparation which has been injected with coloured 

 resin, and macerated in hydrochloric acid. In such preparations, 

 we never find single terminal air-cells, nor do we ever see them 

 pedunculated or opening independently ; but they always open 

 into each other, and coalesce in such a manner, as to form by their 

 union a tube with sinuous walls, and mostly pyriform in shape. 

 These tubes are the finest pulmonary lobules,' or the infundibula 

 of Rossignol. The air-cells on their walls are not disposed singly 

 and at regular intervals, but arc arranged in groups, and even 

 form small secondary recesses, which open in the so-called infun- 

 dibulum. An idea of the whole relation of the parts in question 

 may be best obtained, by regarding each pulmonary lobule as 

 an amphibian lung in miniature : or we may consider the ulti- 

 mate divisions of the bronchia to widen at their ends, and the 

 dilated extremities to be closely beset with numerous racemose 

 groups of vesicles, opening into one another, and into the common 

 cavity. This structure corresponds, then, in its main features 

 with that of other racemose glands. Adrian! has observed in the 

 adult lung, a partial coalescence of the air-cells of a lobule by 

 perforation of their walls, the septum between two adjacent air- 

 cells in a group being reduced to a few isolated threads. 



The smallest bronchial tubes, cri'" to o"i6'"in diameter, arise 

 from the finest lobules by simple diminution in size. At their 

 origin they continue to be surrounded by simple air-cells, which 

 are called parietal, and they, accordingly, have at first sinuous 

 walls. The irregularities soon disappear, and give place to the 

 ordinary smooth appearance, which is observable through the 

 remainder of their course. The size of the air-cells varies very 

 considerably even in healthy lungs, and, in the absence of dila- 

 tation by air, is found to measure after death V'" to ^" to ^~". 

 Every air-vesicle, however, is capable, by virtue of its elasticity, of 

 being distended, without tearing, to double or treble its original 

 size, and of returning afterwards to its previous condition. We 

 shall not err in assuming, that in life, during moderate fulness of 

 the lungs, the air-vesicles arc at least one-third wider than after 

 death ; and that, by the utmost possible deep inspiration, the dila- 

 tation may reach to double the size presented post mortem. In 

 emphysema, dilatation to this extent, and even far beyond it, 

 becomes permanent, and may lead at last to the rupture of the 

 walls of the alveoli of a lobule, or even to the coalescence of the 



