86 



ELEMENTS OF PHYSIOLOGY 



into fibers which by entangling the corpuscles caused the 

 formation of the clot. The serum, or the portion of the 

 blood that remains liquid, is composed of water and albu- 

 min, with traces of sugar, fat, and certain salts. If the 



FlG. 83. Diagram to Illustrate the Process of Coagulation. 



I. Fresh. II. Coagulating. III. Coagulated. 



(Corpuscles and plasma.) (Birth of fibrin.) (Clot and serum.) 



Plasma minus fibrinogen equals serum. Corpuscles plus fibrin equal clot. 



water is -boiled away, the albumin is left as a white jelly. 

 The composition of the clot, serum, and plasma may 

 be shown as follows : 



COAGULATED I 



BLOOD 



I Serum 



( Blood corpuscles 

 1 Fibrin 



J Water J> Plasma 

 1 Albumin 



LIQUID 

 BLOOD 



CIRCULATION OF THE BLOOD 



142. The organ which gives the push or impulse to the 

 blood and causes it to circulate in the tubes or vessels is 

 the heart (Fig. 84). The tubes that conduct the blood 

 away from the heart to the organs and tissues are called 

 arteries. The tubes through which it returns to the heart 

 are called veins. The very small tubes that take the blood 

 from the arteries to the veins where it begins its return 

 journey are called capillaries. The blood must circulate in 

 order that it may go to the digestive organs to get food, 

 to the lungs to get oxygen, and to all the tissues in order to 

 distribute these things, and to carry away waste materials 

 to the organs that will free the body of them. Can you 

 see in your mind the dark color of a piece of beef and 



