; the spleen contains many large
cells that seem to have the power first of "engulfing" and later of
decomposing red corpuscles. A further evidence that the spleen aids
in the removal of worn-out corpuscles is found in the fact that
during diseases that cause a destruction of the red corpuscles, such
as the different forms of malaria, the spleen becomes enlarged.

10 An infected part of the body, such as a boil or abscess, should
never be bruised or squeezed until the time of opening. Pressure
tends to break down the wall of white corpuscles and to spread the
infection. Pus from a sore contains germs and should not, on this
account, come in contact with any part of the skin. (See treatment
of skin wounds, Chapter XVI.)

11 Coagulation is not confined to the blood. The white of an egg
coagulates when heated and when acted upon by certain chemicals, and
the clabbering of milk also is a coagulation.

12 If the blood be stirred or "whipped" while it is coagulating, the
clot may be broken up and the fibrin separated as fast as it forms.
The blood which then remains consists of serum and corpuscles and
will not coagulate. It is known as "defibrinated" blood.

13 Certain substances, called _opsonins_, have recently been shown to
exist in the plasma, that aid the white corpuscles in their work of
destroying germs. The opsonins appear to act in such a manner as to
weaken the germs and make them more susceptible to the attacks of
the white corpuscles.

14 Some of the changes in the blood are very closely related to our
everyday habits and inclinations. For example, a lack of nourishment
in the blood causes hunger and this leads to the taking of food. If
the fluids of the body become too dense, a feeling of thirst is
aroused which prompts one to drink water.

15 Metchnikoff, _The New Hygiene_.

16 A physiological salt solution is prepared by dissolving .6 of a gram
of common salt in 100 cc. of distilled water or pure cistern water.
This solution, having the same density as the plasma of the blood,
does not act injuriously upon the corpuscles.

17 The term "circulation" literally means moving in a circle. While the
blood does not move through the body in a circle, the term is
justified by the fact that the blood flows out continually fr