12 HUMAN PHYSIOLOGY CHAP. 



materials for the cells, and removes from it the waste 

 products of tJie cells. 



12. Uses of the Blood. All the foods we eat are 

 changed in the body so that they become part of the 

 blood, and may be used to keep the cells in a good, 

 healthy condition. The water we drink also gets into 

 the blood and is carried to the cells, where it is of 

 great use. Even the air we breathe finds its way into 

 the blood, which then carries the oxygen to the cells 

 throughout the body. Thus we see that the blood brings 

 oxygen and foods together in the cells in all parts of 

 the body. The chief function of the blood is to carry 

 foods and wastes. The blood is necessary to keep us 

 alive ; to keep us well ; to give us strength to work ; 

 and to make us grow. 



13. What Blood looks like. We have all seen blood 

 and know that it is a bright red liquid. Through a mi- 

 croscope it is not red at all but yellow in color. The 

 whole mass of water of a large lake looks blue, but a 

 small amount does not. And it is just so with the 

 blood ; a drop looks red, but a very small amount as 

 seen under the microscope looks pale yellow. 



Prick yourself with a sharp, clean needle so as to draw a small 

 drop of blood. Examine it with a microscope. Describe what you 

 find. The small masses are red blood corpuscles floating about in 

 the plasma. Do you see larger white masses ? They are white 

 corpuscles. 



14. Composition of Blood. Under the microscope 

 we see thousands of tiny yellow bodies moving about 

 in a colorless liquid. These solids, oddly enough, are 



