160 DISEASES OF THE LUNGS. 



incised surfaces, commonlyof a reddish-black, are marked with 

 bright red spots, variable in size, of which the most superficial 

 communicate with the exterior eminences. They are occa- 

 sioned by the chemical action of the atmospheric air_, 

 remaining within the dilated air-cells of the globules, on 

 the colouring matter of the blood effused into the sur- 

 rounding tissue. 



With the three kinds of dilatation just described, we 

 sometimes meet with dilatation of the small bronchial tubes 

 running to the lobules increased in their volume. These 

 minute divisions, unprovided with cartilaginous rings, have 

 been discovered double the diameter they are in a sound 

 state. The membrane lining them is pale, thin, and coated 

 with a clear and plastic mucus. 



Now and then we find a middle-sized bronchial tube 

 dilated, which is supplying several morbid lobules. This 

 especially happens in emphysema resulting from chronic 

 inflammation of the mucous membrane, accompanied with 

 abundant secretion ; and these dilatations are attended with 

 separation of the cartilaginous rings, and with paleness, 

 ulceration, and even perforation of the internal coat. In 

 this case, the bronchi, and particularly such tubes as are 

 dilated, contain a white, plastic, inodorous mucus. 



Whether it happen that one or more air-cells become 

 suddenly ruptured from some effort, or whether the same 

 happen to air-cells already dilated and attenuated, or whether 

 the breach be the result of ulceration and complete per- 

 foration of the membrane, air makes its escape into the 

 interlobular cellular tissue and produces emphysema. If in 

 this condition the lungs be examined soon after death, the 

 pulmonary lobules will be found more or less isolated, in 

 consequence of the extravasated air separating them from 

 one another. Tiiis stream of air may be made by pressure 

 to pass from one cellule to another, and to form bubbles or 

 vesicles, of an indefinite shape, and of volume varying from 

 that of a lentil to a nut, or even to a large hen^s egg. 

 They occupy particularly the borders and extremities of the 

 lobes, and often have the pleura for their boundary, which 



