THE BLOOD 33 



through a system of connected vessels causes it to escape 

 rapidly from the body whenever openings in these vessels 

 are made. Clots form at such openings and close them up, 

 stopping in this way the flow that would otherwise go on 

 indefinitely. Coagulation, however, does not stop the flow 

 of blood from the large vessels. From these the blood runs 

 with too great force for the clot to form within the wound. 



Time Required for Coagulation. The rate at which coagulation 

 takes place varies greatly under different conditions. It is influenced 

 strongly by temperature; heat hastens and cold retards the process. 

 It may be prevented entirely by lowering the temperature of the 

 blood to near the freezing point. The presence of a foreign substance 

 increases the rapidity of coagulation, and it has been observed that 

 bleeding from small wounds is more quickly checked by covering them 

 with linen or cotton fibers. The fibers in this case hasten the process 

 of coagulation. 



Quantity of Blood. The quantity of blood is estimated to be 

 about one thirteenth of the entire weight of the body. "This for the 

 average individual is an amount weighing nearly twelve pounds and 

 having a volume of nearly one and one half gallons. About 46 per cent 

 by volume of this amount is made up of corpuscles and 54 per cent of 

 plasma. Of the plasma about 10 per cent consists of solids and 90 

 per cent of water, as already stated. 



Functions of the Blood. The blood is the great carry- 

 ing, or distributing, agent in the body. Through its move- 

 ments (considered in the next chapter) it carries food and 

 oxygen to the cells and waste materials from the cells. 

 Much of the blood may, therefore, be regarded as freight 

 in. the process of transportation. The blood also carries, 

 or distributes, heat. Taking up heat in the warm parts of 

 the body, it gives it off at places having a lower tempera- 

 ture. This enables all parts of the body to keep at about 

 the same temperature. 



In addition to serving as a carrier, the blood has anti- 

 septic properties, i.e., it destroys disease germs. While 



