92 GLANDS. 



structure of^the The constituent parts of a pulmonary vesicle, pass- 

 ing from without inwards, are, 1st, basement mem- 

 brane; 2d, its epithelial investment. The first is 

 . formed by an extremely delicate web of elastic fibres ; 



different openings, converge to a point a short distance from the surface 

 of the lung. It will be known that they pass to a common point, as, by 

 moving one of the bristles gently, it will act upon the others. Having 

 placed bristles in all the air-sacs which converge to this spot, the bristles 

 should be left in their position, and the bronchial tube should be laid 

 bare on its proximal side, down to its termination, i. e. the lung sub- 

 stance covering it should be removed, care being taken to stop just 

 before reaching the spot where it communicates with the air-sacs. The 

 number of bristles communicating with the spot thus exposed, will show 

 the number of air-sacs belonging to one group. The termination of the 

 bronchial tube will be seen to be somewhat expanded, and the air-sacs 

 will be found, many of them, to communicate with it by a circular ori- 

 fice, which is smaller than the sac itself." . . . . " When the bron- 

 chial tube has been exposed in the way I have mentioned, and the mode 

 of communication with the air-sacs observed, a section may be made 

 longitudinally through one or more of the latter ; it will be then seen 

 that the sacs lie side by side, and that they occasionally give off smaller 

 sacs ; the manner also in which they divide, and the mode in which 

 they terminate, will be observed. It will also be seen, that as each 

 bronchial tube approaches its termination, it has here and there through- 

 out its circumference, small circular orifices, which are the commencement 

 of small canals, leading to groups of air-sacs or lobulettes ; and it will 

 further be seen that the tube itself, at its termination, has a number of 

 alveoli in its walls. . . . 



" Another very excellent way of examining the terminal bronchial 

 tubes, and the commencement of the air-sacs, is to soak a piece of lung 

 that has been injected, inflated, and dried, in spirits for some time, and 

 when the piece is well saturated, to dissect it under the microscope. By 

 imbibition of the spirit the mass of lung swells, and the air tubes and sacs 

 remaining distended, the parts assume nearly the size and shape they have 

 in life. When such a piece is examine^, very frequently on opening the 

 bronchial tubes and following them to their end, their alveoli may be 

 plainly seen, as well as the orifices leading to the air-sacs, and the band 

 of elastic fibres which surrounds the opening into each sac becomes 

 apparent." pp. 182-14T. (Ed.} 



