to prevent the spread of germs through the body. In a similar manner they
also prevent the germs from boils, abscesses, and sore places in general
from getting to and infecting other parts of the body.(10) Another
function ascribed to the white corpuscles is that of aiding in the
coagulation of the blood (page 31); and still another, of aiding in the
healing of wounds.

*Plasma.*—The plasma is a complex liquid, being made up of water and of
substances dissolved in the water. The dissolved substances consist mainly
of foods for the cells and wastes from the cells.

1. _The foods_ represent the same classes of materials as are taken in the
daily fare, _i.e._, proteids, carbohydrates, fats, and salts (Chapter IX).
Three kinds of proteids are found in the plasma, called _serum albumin_,
_serum globulin_, and _fibrinogen_. These resemble, in a general way, the
white of raw egg, but differ from each other in the readiness with which
they coagulate. Fibrinogen coagulates more readily than the others and is
the only one that changes in the ordinary coagulation of the blood. The
others remain dissolved during this process, but are coagulated by
chemical agents and by heat. While all of the proteids probably serve as
food for the cells, the fibrinogen, in addition, is a necessary factor in
the coagulation of the blood (page 31).

The only representative of the carbohydrates in the plasma is _dextrose_.
This is a variety of sugar, being derived from starch and the different
sugars that are eaten. The _fat_ in the plasma is in minute quantities and
appears as fine droplets—the form in which it is found in milk. While
several mineral salts are present in small quantities in the plasma,
_sodium chloride_, or common salt, is the only one found in any
considerable amount. The mineral salts serve various purposes, one of