e explanation of a blood picture of this kind, apart from the purely
anaemic changes, is by no means easy, as Epstein rightly observes. The
appearance of myelocytes is most readily explained by a direct
stimulation of the remaining bone-marrow by the surrounding masses of
tumour. In this, the mechanical factor is less concerned than the
chemical metabolic products of the tumour masses; which at first act on
the adjacent tissue in specially strong concentration, and also in a
negatively chemiotactic manner on the wandering cells. This view
receives support from the careful work of Reinbach on the behaviour of
the leucocytes in malignant tumours. Out of 40 cases examined, in only
one, of lymphosarcoma complicated with tuberculosis, were myelocytes
found in the blood, amounting to about 0.5-1.0% of the white blood
corpuscles. The autopsy shewed isolated yellowish white foci of growth
in the bone-marrow, reaching the size of a sixpenny piece. Bearing in
mind that in none of the other 39 cases were myelocytes demonstrated,
one does not hesitate to explain their presence in the blood in this
single case by the metastases in the bone-marrow. The small extent of
the latter is likewise the cause of the small percentage of the
myelocytes.

In explaining the presence of the megaloblasts in the blood of Epstein's
patient we must keep before us what we have said elsewhere on this kind
of cell. They are not present in the normal bone-marrow; they arise on
the contrary, according to our view, when a specific morbid agent acts
upon the bone-marrow, as we must assume is the case in the pernicious
forms of anaemia. In the cases of anaemia from tumours, in which we find
megaloblasts in large numbers in the blood, we must likewise assume that
chemical stimuli proceed from the tumours, leading to the formation of
megaloblasts in the bone-marrow.

The presence of megaloblasts in the bone-marrow does not itself cause
their appearance in the blood, for in pernicious anaemia the bone-marrow
may be filled with megaloblasts, and yet only very scanty examples are
to be found in the blood. Whether the emigration of the megaloblasts
from the bone-marrow into the blood-stream is in general to be referred
to chemical stimuli, as it is in the particular case of Epstein's, or to
mechanical causes, cannot at present be decided.

The bone-marrow may be replaced by typical lymphatic tissue, as well as
by the substance of malignant tumours. The former occ