210 ELEMENTARY BIOLOGY. [CHAP. 



3. 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 

 /3. 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. 



% /?. 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. 



4. Examine a drop of frog's blood with the microscope 

 (J or I 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). 



