ELEMENTARY BIOLOGY. [CHAP. 



Place a small drop of water on a bit of a thin cover- 

 glass, and place the bit, with the water downwards, 

 gently on the web : then examine the following points 

 with \ or \ obj. ; note 



a. The 'walls of arteries , capillaries, and veins. 



a. The arterial walls, tolerably thick, seen as a 



clear well-defined band on each side of the 



blood-stream. 

 p. The capillary walls ; difficult to see ; merely 



a thin somewhat more transparent boundary 



line. 



y. The venous walls ; much like the arterial. 



b. The blood-flow in the small arteries of the web. 



a. The rapid stream in the middle, containing 



most of the red corpuscles. 

 ft. The slower stream along the edge (inert 



layer), containing many colourless corpuscles. 



c. The flow in the capillaries : much slower than in 

 the arteries ; the frequent distortion of the red 

 corpuscles in the capillaries from pressure, &c. ; 

 their elasticity as indicated by the readiness with 

 which they recover their shape when the cause 

 of distortion is removed; the way the white 

 corpuscles creep along, with a tendency to stick 

 to the capillary wall. 



Examine a drop of frog's blood with the microscope 

 (J-or-| obj.). Sufficient blood to supply a whole class 

 for this purpose can be obtained by killing one frog 

 and opening its heart. 



It consists of solid bodies (corpuscles) floating in 

 fluid (plasma). 



