THE BLOOD l6l 



65. Human blood may be obtained without pain by tying a string 

 snugly around the finger. After a moment make a quick prick with 

 a clean needle upon the back of the finger just behind the nail. Remove 

 the string, and a drop of blood will flow which can be examined under 

 the microscope. Notice the circular shape of the red cells and the 

 absence of nuclei. Notice that they tend to arrange themselves in rows 

 like piles of coins. 



66. Place a drop of salt water on the slide by one edge of the cover 

 glass, and notice that the cells become shrunken. 



67. White blood cells are too few in number to be readily found 

 within a specimen of blood, but they form most of the white matter of 

 a pimple or boil. Prepare and examine a specimen, and notice the 

 dark specks scattered through the cells, and the nuclei which may be 

 three in number in each cell. Add a drop of vinegar and notice that 

 each cell becomes transparent, only the nuclei remaining visible. 



68. With a little care the movement of the white cells may be shown 

 in frog's blood. Prepare a fresh specimen of frog's blood upon a slide 

 slightly warmed. After a little search an irregularly shaped white blood 

 cell can usually be found. Watch it carefully, and it will be seen slowly 

 changing its shape exactly as an ameba changes, only more slowly. A 

 magnifying power of at least 200 diameters will be necessary. 



69. Prepare a specimen of blood for the microscope. (See demon- 

 stration No. 65.) At the edge of the cover glass drop a tiny bit of 

 alcohol. Notice how the red blood cells shrivel and become irregular 

 in form, because the alcohol takes away their water. 



REVIEW TOPICS 



1. Describe the blood. 



2. Describe the red blood cells. 



3. Describe the white blood cells. 



4. Describe the blood plasma. 



5. Describe the clotting of blood. 



6. Show what was meant in olden times by the terms good 



and bad blood and good and bad humored. 



7. Describe the blood in some of the lower forms of living 



beings. 



8. Describe the spleen and its use. 



OV. PHYSIOL. II 



