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 carrying, or
distributing, agent in the body. Through its movements (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 temperature. This enables all parts of the body to
keep at about the same temperature.

In addition to serving as a carrier, the blood has antiseptic properties,
i.e., it destroys disease germs. While this function is mainly due to the
white corpuscles, it is due in part to the plasma.(13) Through its
coagulation, the blood also closes leaks in the small blood vessels. The
blood is thus seen to be a liquid of several functions.

[Fig. 12]


Fig. 12—*A balanced change* in water. The level remains constant although
the water is continually changing; suggestive of the changes in the blood.


*Changes in the Blood.*—In performing its functions in the body the blood