202 ELEMENTARY BIOLOGY. [XIII. 



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 cor- 

 puscles creep along, with a tendency to stick 

 to the capillary wall. 



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

 (J or J 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). 



a. The red corpuscles. 



a. Their form: oval when seen in front face; 

 almost linear in profile but slightly swollen at 

 the centre. 



/5. Their size: their length, breadth, and thick- 

 ness; measure. 



7. Their colour : pale yellow, when seen individu- 

 ally ; redder if a thick mass of them is looked 

 at. 



8. Their structure : they are homogeneous for the 

 most part, but possess a round granular central 

 nucleus. 



e Treat with water ; they swell up and^ become 

 more spherical ; their colouring matter is gra- 

 dually discharged ; the nucleus is rendered very 

 evident, and ultimately all the rest of the 

 corpuscle disappears. 



Treat with dilute acetic acid ; results same as 

 with water, but produced more rapidly. 



