46 HUMAN PHYSIOLOGY .CHAP. 



blood. It is in these small lobules that the air we 

 breathe comes in contact with the blood. 



1. Procure a sheep's lungs and notice the size, shape, color, and 

 texture. Notice the air tubes leading to each lung. Will the lungs 

 float in water ? 



2. Blow up the lungs by breathing into the windpipe. 



FIG. 19. Showing the trachea, right lung, and the bronchial tubes of the left 

 lung (Zuppke). 



49. Covering of the Lungs. Each lung is closely 

 covered with a thin, delicate, saclike serous membrane 

 called ihefl/eura. The outer part of this sac lines the 

 walls of the chest, while the inner part covers the lungs. 

 There is a small amount of fluid in the sacs which serves 

 to keep the membrane moist, and so prevents friction 

 and disease which would result from the constant rub- 



