EXERCISE 75 



I Problem. What is the make up of the human blood ? 

 What to use. Compound microscope ; glass slide ; cover glass ; gas or alcohol flame ; sharp needle ; 

 normal salt solution (made by dissolving about a teaspoonful of common salt in a pint of water). 1 



What to do. Press the thumb hard against the joint of the index finger until the skin is tight 

 and red. With the other hand pass the needle through the flame. After waiting a moment for it to 

 cool, prick the tight skin of the thumb with a smart stroke. Collect the drop of blood in the middle 

 of the glass slide. Add a drop of salt solution. Cover with the cover glass. Examine under the 

 microscope, first with the low power, then with the high. 



Record. Make a drawing to show all the different structures you can find. 



NOTE. The yellowish disks are the red corpuscles. Larger, irregular bodies, not so numerous, are the white corpus- 

 cles. The clear liquid in which the corpuscles float is the plasma. These three are the chief constituents. There are other 

 structures in the blood, but they are harder to see. 



Question. What element of the blood is deficient in a pale person who is said to be anaemic ? 



1 It is not necessary to prepare salt solution for your own use ; there is probably some on hand in the laboratory. 



[81] 



