66 RESPIRATORY SYSTEM. 



bronchus. Recognise the large pulmonary artery and vein 

 surrounded by loose peribronchial connective tissue, and the 

 sharp delimitation of the latter by the vesicular tissue of the 

 lung. Search for the small bronchial arteries scattered around 

 the bronchus (which convey arterial blood to its tissues) and 

 the nerves with frequent ganglia which accompany them. 

 Endeavour to trace in the surrounding lung substance the 

 expansion of the bronchus into the vesicular tissue and 

 examine the latter. 



Silvered Lung 1 of kitten or other young mammal. The freshly 

 excised lung is filled with 0"25P- C - solution AgN0 3 through a funnel 

 tied into the trachea, the air driven out by gentle squeezing, then 

 alternately emptied and refilled once with silver solution, and twice 

 with methylated spirit. The second charge of the latter being made 

 to distend the lung is retained by ligaturing the trachea,' the whole 

 being finally immersed in spirit. When rigid, 48 hours, cut into con- 

 venient pieces and continue the hardening 14 or more days in sunlight 

 (c. G, s. 19, m. F. or B.) 



(L) Recognise the bronchi, find an L.S. bronchiole at its 

 infundibular expansion (H\ note the cubical epithelium of 

 the bronchiole, the absence of cartilage and thinness of its 

 walls. Study closely how the vesicular recesses (air vesicles), 

 multiple saccular expansions, are connected with the walls of 

 the infundibular end of the bronchiole. The portions which 

 remain of the latter may be recognised around the vesicular 

 orifices by their covering of cubical epithelium. The endothelial 

 lining of the air sacs is outlined by the action of the silver, 

 each cell possessing a nucleus. Smaller cells stained brown 

 occur singly or in groups of two or three between the larger 

 clear ones, and may be regarded as germinal cells or as 

 pseudostomata connected with the perivesicular lymphatics. 

 Distinguish on the outer surface of the lung the pleural 

 epithelium and connective tissue. 



