212 ELEMENTARY PHYSIOLOGY. [XX. 



to leave the lung fairly distended. Pass another 

 thread under the lung and tie it close below the 

 mouth of the cannula. Holding up the thread 

 cut away the lung from its attachments and 

 place^it in gold chloride 0'5 p.c. solution for 

 about fifteen minutes. Then remove it to water, 

 cut it open longitudinally, and get rid of the 

 excess of gold solution by gently shaking the 

 lung in water once or twice renewed. To reduce 

 the gold expose it to light for about 24 hours in 

 water acidulated with acetic acid. 

 Whilst cutting open the lung note that it is a 

 simple sac with a smooth inner surface. 

 Mount a piece in glycerine with the inner surface 

 uppermost, and observe with a high power 



a. The nuclei of the epithelium cells, 



occurring in the inter-capillary fossoe in 

 groups of two to four. Sometimes a nucleus 

 may be seen to be surrounded by a smnll 

 amount of protoplasm coloured violet or red- 

 purple like the nucleus. The cell outlines 

 are rarely to be made out. 



6. The close capillary network running between 

 the nuclear groups. In this will probably be 

 seen blood corpuscles with deeply coloured 

 nuclei. On focussing below the capillaries the 

 long stained nuclei belonging to the coat of 

 unstriated muscular fibres may be seen. 



2. Distend the lungs of a frog with 30 p.c. alcohol ; 

 ligature each lung at its origin and place one (a) 



