XXI V] LUNG 189 



The alveoli as roundish areas of various size; in 

 many the central part is simply a space, others show 

 the wall as a thin nucleated membrane ; the outlines of 

 the flat cells of the membrane are not very distinct 

 (cp. Demons. 3) but patches of two or more small cells 

 may be seen amongst larger ones. 



Irregular spaces larger than alveoli ; these are the 

 respiratory bronchioles, the short passages into 

 which these divide, and the infundibula branching 

 from the passages. They all give off alveoli, but 

 the respiratory bronchioles do so from a part only of 

 their periphery. 



The epithelium of the atria and the infundibula resembles 

 that of the alveoli except that the groups of small cells are 

 larger; the epithelium of the respiratory bronchioles consists 

 partly of non-ciliated cells either cubical or flat, partly of patches 

 of ciliated cells, muscular fibres may be present in the wall. 



4. Section of mammalian lung, the blood vessels 

 of which have been injected ; mount in balsam. 



Observe the close-set capillary network in the 

 alveolus, and the branching of the large vessels. 



5. Cut out a lung from a recently killed newt, open it longi- 

 tudinally, divide into two parts and spread them out, inner 

 surface uppermost, on separate slides, being careful not to rub 

 off the epithelium. 



a. Treat with silver nitrate as in Lesson xvn. 2, but do 

 not transfer from clove oil to balsam until the outlines of the 

 surface cells are visible. 



6. Make a moist film preparation and fix with alcohol. 

 Stain, but not very deeply, with hsematoxylin and eosin. 



Observe The nuclei of the surface cells of the lung, occurring 

 in groups of two to six. The outline of the cells (silver prepara- 



