THE LUNG 8. 



237 



Bronchitis, or "a cold on the chest," is an inflamma- 

 tion of the membrane lining the bronchial tubes, in con- 

 sequence of which it swells, and secretes an extra amount 

 of mucus. The swelling and secretion tend to close the 

 tabes and interfere with the free passage of air in breathing. 



The Lungs consist of the bronchial tabes and their ter- 

 minal dilatations, together with blood-vessels, lymphatics, 

 and nerves, all bound firmly together by elastic tissue. 

 The expansions called " air-cells" * at the end of each final 

 branch of a bronchial tube (Fig. 

 66) are relatively very large, 

 and their surface is still fur- 

 ther increased by the pouches 

 (, V) which project from them. 

 Their walls are highly elastic, 

 and contain a close network of 

 capillary blood-vessels, supplied 

 by the pulmonary artery and 

 emptying into the pulmonary 

 veins. Through the extremely 

 thin lining of the air-cell, and 



., . , . *ii ii -n FlG - 66. Two alveoli of the lung 



the thin Wall OI the Capillaries highly magnified. 6, 6, the air-cells, 

 . . , or hollow protrusions of the alveo- 



imbedded. Ill It, OXygen IS au- lus, opening into its central cavity; 



c, terminal branches of bronchial 



sorbed by the blood from the tube. 



air in the air-cell and carbon dioxide given up to 



It 



"What is bronchitis? How does an attack of bronchitis interfere 

 with breathing? 



Of what do the lungs consist? What are the air-cells? How is 

 their surface increased? What do their walls contain? By what are 

 their capillaries filled, and into what do they empty? What inter- 

 change between blood and air occurs in the air-cells of the lungs? 



* Cell is here used in its primitive sense of a small chamber or cavity (Latin, 

 cellula), and not in its modern histological signification, as one of the distinct 

 pieces of living matter recognized by the microscope as serving to build up the 

 body by their accumulation and co operation. 



