than do the red, and hence accumulate in the vessels lining the inner
surface and later become attached to this and cease to move forward.
The attached corpuscles then begin to move as does an amoeba, sending
out projections, some one of which penetrates the wall, and following
this the corpuscles creep through. Red corpuscles also pass out of the
vessels, this taking place in the capillaries; the white corpuscles,
on the other hand, pass through the small veins. Not only do the white
corpuscles pass through the vessels, but the blood fluid also passes
out. The corpuscles which have passed into the tissue around the
vessels are carried away by the outstreaming fluid, and the web
becomes swollen from the increased amount of fluid which it contains.
The injured area of the web is more sensitive than a corresponding
uninjured area and the foot is more quickly moved if it be touched. If
the injury has been very slight, observation of the area on the
following day will show no change beyond a slight dilatation of the
vessels and a great accumulation of cells in the tissue.

Everyone has experienced the effect of such changes as have been
described in this simple experiment. An inflamed part on the surface
of the body is redder than the normal, swollen, hot and painful. The
usual red tinge of the skin is due to the red blood contained in the
vessels, and the color is intensified when, owing to the dilatation,
the vessels contain more blood. The inflamed area feels hot, and if
the temperature be taken it may be two or three degrees warmer than a
corresponding area. The increased heat is due to the richer
circulation. Heat is produced in the interior of the body chiefly in
the muscles and great glands, and the increased afflux of blood brings
more heat to the surface. A certain degree of swelling of the tissue
is due to the dilatation of the vessels; but this is a negligible
factor as compared with the effect of the presence of the fluid and