When an inflamed area is examined, after twenty-four hours, by
hardening the tissue in some of the fluids used for this purpose and
cutting it into very thin slices by means of an instrument called a
microtome, the microscope shows a series of changes which were not
apparent on naked eye examination. The texture is looser, due to the
exudate which has dilated all the spaces in the tissue. Red and white
corpuscles in varying numbers and proportions infiltrate the tissue;
all the cells which belong to the part, even those forming the walls
of the vessels, are swollen, the nuclei contain more chromatin, and
the changes in the nuclei which indicate that the cells are
multiplying appear. The blood vessels are dilated, and the part in
every way gives the indication of a more active life within it. There
are also evidences of the tissue injury which has called forth all the
changes which we have considered. (Fig. 15.)

[Illustration: FIG. 15--A SECTION OF AN INFLAMED LUNG SHOWING THE
EXUDATE WITHIN THE AIR SPACES. Compare this with Fig 6. Fig 15 is from
the human lung, in which the air spaces are much larger than in the
mouse.]

The microscopic examination of any normal tissue of the body shows
within it a variable number of cells which have no intimate
association with the structure of the part and do not seem to
participate in its function. They are found in situations which
indicate that these cells have power of active independent motion. In
the inflamed tissue a greatly increased number of these cells is
found, but they do not appear until the height of the process has
passed, usually not before thirty-six or forty-eight hours after the
injury has been received. The numbers present depend much upon the