336 DISEASES OF THE RESPIRATORY ORGANS. 



THE LUNGS, 



ATELECTASIS. 



Atelectasis is a condition in which the lung is compressed 

 or collapsed, so that there is an absolute absence of air from 

 the air- vesicles. 



Congenitally it occurs, especially posteriorly and at the 

 base of the lungs, from some mechanical obstruction of the 

 air-passages, as the presence of meconium ; or an inability to 

 take a full inspiration, as the result of extreme weakness. 

 Under these circumstances the term apneumatosis is some- 

 times applied. The affected areas are bluish, and so solid 

 that if a portion is thrown into water it sinks. 



Later in life a large pleuritic effusion, or a Avound in the 

 chest-wall, may result in the collapse of a whole lung. A 

 lobular collapse occurs in broncho-pneumonia, and is supposed 

 to result from a valve-like obstruction of a bronchiole by a 

 plug of mucus, which cannot be dislodged by inspiration, but 

 permits the air to escape from the lobules supplied. The 

 tissue is dry and tough, has a firm, flesh-like feel, does not 

 crepitate, and sinks if placed in water. If the condition per- 

 sists, there is finally an entire and permanent obliteration of 

 the air-vesicles by an overgrowth of connective tissue. 



EMPHYSEMA . 



Interstitial emphysema is a condition analogous to emphysema 

 of subcutaneous tissues ; there is an accumulation of air in 

 the connective-tissue septa between the lobules of the lung as 

 the result of rupture of an air-vesicle. It occurs most fre- 

 quently in the course of whooping-cough or broncho-pneu- 

 monia in young children ; and from excessive straining-efforts 

 in parturition, defecation, coughing, etc. 



By vesicular emphysema we understand a dilatation of the 

 air-vesicles which occurs as the result of a weakened condi- 

 tion of the lung-tissue from inflammatory or degenerative 

 processes, lessening its ability to resist increased pressure 

 within, from such causes as chronic cough, blowing of wind- 

 instruments, etc. The lungs are considerably larger than 

 normal j there is a gritty feeling on section, and the dilatation 



