is chiefly by means of their activity that other sorts of substances
are removed. They often contain dead cells or cell fragments, and when
hæmorrhage takes place in a tissue they enclose and remove the
granules of blood pigment which result. They often join together,
forming connected masses, and surround such a foreign body as a hair,
or a thread which the surgeon places in a wound to close it. They may
destroy living cells, and do this seemingly when certain cells are in
too great numbers and superfluous in a part, their action tending to
restore the cell equilibrium. The foreign cells do even more than
this: they themselves may be devoured by the growing cells of the
tissue, seemingly being actuated by the same supreme idea of sacrifice
which led Buddha to give himself to the tigress.

The explanation of most of the changes which take place in
inflammation is obvious. It is a definite property of all living
things that repair takes place after injury, and certain of the
changes are only an accentuation of those which take place in the
usual life; but others, such as the formation of the exudate, are
unusual; not only is the outpouring of fluid greatly increased, but
its character is changed. In the normal transudation[2] the substances
on which the coagulation of the blood depends pass through the vessel
wall to a very slight extent, but the exudate may contain the
coagulable material in such amounts that it easily clots. The
interchange between the fluid outside the vessels and the blood fluid
takes place by means of filtration and osmosis. There is a greater
pressure in the vessels than in the fluid outside of them, and the
fluid filters through the wall as fluid filters through a thin
membrane outside of the body. Osmosis takes place when two fluids of
different osmotic pressure are separated by animal membrane.
Difference in osmotic pressure is due to differences in molecular