oncerned.

This toxaemia affects the marrow and through it the blood, the
gastro-intestinal apparatus and the nervous system, especially the
spinal cord, in different proportions in different cases. The effect
upon the marrow is to alter the type of red corpuscle formation, causing
a reversion to the embryonic condition, in which the nucleated red
corpuscles are large (megaloblasts), and the corpuscles in the blood
formed from them are also large, are apparently ill suited to the needs
of the adult, and easily break down, as the deposits of iron in the
liver, spleen, kidneys and marrow prove. Whether this reversion is due
to an exhaustion of the normal process or to an inhibition of it is not
definitely known. The result is that the circulating red corpuscles are
enormously diminished; it is usual to find 1,000,000 or less in the
cubic millimetre instead of the normal 5,000,000. Though the haemoglobin
is of course absolutely diminished, it is always, in severe cases,
present in relatively higher percentage than the red corpuscles, because
the average red corpuscle is larger and contains more haemoglobin than
the normal. The large nucleated red corpuscles (megaloblasts) with which
the marrow is crowded, often appear in the blood.

Other anaemias, such as those known as _lymphadenoma_, or Hodgkin's
disease, _splenic anaemia_, _chloroma_, _leucanaemia_ and the _anaemia
pseudo-leucaemica_ of children, need not be described here, as they are
either rare or their occurrence or nature is still too much under
discussion.

Leucocytosis.

The number and nature of the leucocytes in the blood bears no constant
or necessary relation to the number or condition of the red corpuscles,
and their variations depend on entirely different conditions. The number
in the cubic millimetre is usually about 7000, but may vary in health
from 5000 to 10,000. A diminution in their number is known as
_leucopenia_, and is found in starvation, in some infective diseases, as
for example in typhoid fever, in malaria and Malta fever, and in
pernicious anaemia. An increase is very much more frequent, and is known
as _leucocytosis_, though in this term is usually connoted a relative
increase in the proportion of the polymorphonuclear neutrophile
leucocytes. Leucocytosis occurs under a great variety of conditions,
normally to a slight extent during digestion, during pregnancy, and
after violent exercise, and abnormally after haemorrhage, in the cours