134 STUDENTS HISTOLOGY 



5 The lining epithelial cells, (a) Those remaining attached 

 to the edges of the wall, D. (&) Detached cells. E. (c) Groups 

 partly detached, F, F. 



6. The divided pulmonary artery, G. (A medium - sized bron- 

 chial tube existed in the section immediately to the left of the 

 artery.) 



FCETAL LUNG 



Harden the lung of a foetus, preferably human, in Miiller's or Orth's 

 fluid. After washing, finish hardening in alcohol ; imbed in celloidin; cut; 

 stain with haematoxylin and eosin; mount in balsam. 



Observe the polyhedral form of the epithelial cells lining the 

 alveoli. A few such polyhedral cells can be demonstrated in the 

 alveoli of the adult lung with silver staining, and they correspond 

 to the polyhedral cells of the terminal bronchioles. It appears 

 that the plate -like cells lining the alveoli of the adult lung are 

 derived from the polyhedral cells of the foetal lung, which become 

 flattened from the distension which they undergo when the alveoli 

 are inflated. 



