e
of inflammations and many infective diseases, in malignant disease, in
such toxic states as uraemia, and after the ingestion of nuclein and
other substances. It does not occur in some infective diseases, the most
important of which are typhoid fever, malaria, influenza, measles and
uncomplicated tuberculosis. In all cases where it is sufficiently severe
and long continued, the reserve space in the bone-marrow is filled up by
the active proliferation of the leucocytes normally found there, and is
used as a nursery for the leucocytes required in the blood. In many
cases leucocytosis is known to be associated with the defence of the
organism from injurious influences, and its amount depends on the
relation between the severity of the attack and the power of resistance.
There may be an increase in the proportions present in the blood of
lymphocytes (_lymphocytosis_), and of eosinophile cells
(_eosinophilia_). This latter change is associated specially with some
forms of asthma, with certain skin diseases, and with the presence of
animal parasites in the body, such as ankylostoma and filaria.

Leucaemia.

The disease in which the number of leucocytes in the blood is greatest
is _leucocythaemia_ or leucaemia. There are two main forms of this
disease, in both of which there are anaemia, enlargement of the spleen
and lymphatic glands, or of either of them, leucocytic hypertrophy of
the bone-marrow, and deposits of leucocytes in the liver, kidney and
other organs. The difference lies in the kind of leucocytes present in
excess in the blood, blood-forming organs and deposits in the tissues.
In the one form these are lymphocytes, which are found in health mainly
in the marrow, the blood itself, the lymph glands and in the lymphatic
tissue round the alimentary canal; in the other they are the kinds of
leucocytes normally found in the bone-marrow-myelocytes, neutrophile,
basophile and eosinophile, and polymorphonuclear cells, also
neutrophile, basophile and eosinophile. The clinical course of the two
forms may differ. The first, known as lymphatic leucaemia or
_lymphaemia_, may be acute, and prove fatal in a few weeks or even days
with rapidly advancing anaemia, or may be chronic and last for one or
two years or longer. The second, known as spleno-myelogenous leucaemia
or _myelaemia_, is almost always chronic, and may last for several
years. Recovery does not take place, though remissions may occur. The
use of the X-rays has