THE PULMONARY ALVEOLI 



129 



the capillaries themselves, inasmuch as they are covered with a 

 layer of flat cells. These cells, constituting the parenchyma of the 

 lung, have the power, on the one hand, of selecting such material 

 from the air as may be required, passing it on to the blood in the 

 capillaries; and, on the other, of removing effete material from the 



FIG. 86. 



DIAGRAM OP AN ULTIMATE PULMONARY LOBULE. 



A. A terminal bronchiole. 



B. The air-sacs or alveoli. 



blood, transferring it to the atmospheric contents of the air -sacs 

 for exhalation. 



The air -sacs or alveoli are not unlike minute bladders. Their 

 diameter about equals that of a terminal bronchus; viz., from one- 

 fourth to one -eighth, of a millimeter. A group of these alveoli are 

 associated in the manner shown in Fig. 86, their contiguous walls 



FIG. 87. DIAGRAM SHOWING AN ULTIMATE PULMONARY LOBULE IN LONGITUDINAL 

 SECTION, SHOWING THE MANNER IN WHICH THE ALVEOLI ARE ASSOCIATED IN 

 CONNECTION WITH A TERMINAL BRONCHIOLE. 



A. Terminal bronchiole entering. 



B. The infundibuhim. 



C. C, C. Alveoli. 



fusing and all opening into a common cavity, the infundibulum . 

 The whole is in connection with a terminal bronchiole (vide Fig. 

 87). A primary lobule having been thus constructed, several are 

 associated and united to a slightly larger bronchial twig, and there 

 results one of the polyhedral lobules, previously mentioned as 

 i 



