3^4 



LOBULES OF THE LUNG. 



[SF.CT. I77. 



Fig. 159. 



lobules themselves. In a recent collapsed lung, the form of the 

 air-cells is mostly roundish or oblong, becoming polyhedral, in an 

 inflated or injected lung, inconsequence of their mutual flattening; 

 the air-cells of the surface of the lungs invariably appear poly- 

 gonal, and their external sides are always nearly equal. 



The lobulated structure of the lung is not nearly so distinct in 

 the adult as in younger individuals and in animals. It is, there- 

 fore, advisable to begin the investigation of this structure on the 



lung of a child. Here each single 

 lobule is to be found distinctly sepa- 

 rated from all others by connective tissue, 

 and may be isolated, so as to exhibit 

 the tolerably regular pyramidal form 

 of the superficial lobules, and the more 

 irregular shape of the internal ones. 

 In the adult, these ultimate lobules, 

 ranging in size from \'" to 1'", are still 

 present, but are so intimately blended, 

 that even, upon the surface of the lung 

 their outlines are difficult of recog- 

 nition; while in the interior of the 

 organ, the structure formed by their 

 union appears at first sight homo- 

 geneous, somewhat as in the liver. 

 On the other hand, the secondary lobules, \, h, to 1 inch in size 

 (' lobules ' of some authors), are generally distinct, even in adults, 

 especially when the boundaries of these lobules are marked out by 

 streaks of pigment deposited in the interjacent connective tissue, as 

 is often the case in grown persons. These lobules last mentioned, 

 united by an abundant interstitial tissue, make up the well-known 

 large ' lobes ' of the lung. Thus the lung, as a whole, is composed 

 of larger and smaller segments, which again are made up of air- 

 cells and minute bronchia. Each of these segments is in connexion 

 with one, and one only, of the larger bronchial tubes, which have 

 arisen from the main air- passages in certain definite groups. 



§ 177. The intimate structure of the bronchi and air-cells is as 

 follows. — The bronchi are, in the main, constructed like the trachea 

 and its branches; still some differences present themselves even 

 from the commencement, and these increase more and more as 

 the bronchia are traced onwards. Two coats may, for the sake of 

 convenience, be distinguished upon them : an outer fibrous coat, 



Exterior surface of the injected lung 

 of a cow, after Harting; magnified HO 

 times, a a. Air-cells, b b. Borders 

 of the smallest lobules or infundibula 

 (Rossignol). 



