is very small, and it is therefore hard
to make out the shape of the nucleus without the use of difficult
methods. In triacid preparations the granulation is unstained, and the
mast cells appear as clear, polynuclear cells, free from granules.

* * * * *

So much for the colourless cells in the blood of the normal adult.

In pathological cases, not only do the forms so far mentioned occur in
altered numbers, but abnormal cells also make their appearance. To these
belong:

1. =Mononuclear cells with neutrophil granulation.= ("=Myelocytes=,"
Ehrlich.) Generally they are bulky, with a relatively large, faintly
staining nucleus, often fairly centrally placed, and equally surrounded
by protoplasm on all sides. A fundamental distinction from the large
mononuclear cells lies in the fact that the protoplasm exhibits a more
or less numerous neutrophil granulation. Besides the larger myelocytes,
much smaller forms, approximating to the size of the erythrocytes are
also found. All transitions between these two stages are likewise met
with. In contradistinction to the polynuclear neutrophil elements, these
mononuclear forms shew no amoeboid movement on the warm stage. They
form a constant characteristic of myelogenic leukaemia, and in these
cases generally occur in large numbers.

Reinbach has found them in a case of lymphosarcoma with metastases in
the bone-marrow. A. Lazarus observed their transitory occurrence in
moderate number in a severe posthaemorrhagic anaemia. M. Beck observed
them in the blood of a patient with severe mercury poisoning. They are
also frequently found in children's diseases, especially in _anaemia
pseudoleukaemica infantum_. K. Elze established their presence in a boy
of 15 months, suffering from a slowly progressing tuberculosis of the
lymphatic glands.

The appearance of myelocytes in infectious diseases is particularly
interesting. Rieder had previously demonstrated that myelocytes may be
present in acute inflammatory leucocytoses; and recently a thorough
work by C. S. Engel has appeared upon the occurrence of myelocytes in
diphtheria. Engel discovered the interesting fact, that myelocytes are
often to be found in children suffering from diphtheria, and further
made the important observation that a high percentage of myelocytes
(3.6-16.4% of the white elements) only occurs in severe cases, and
points to an unfavourable prognosis. Myelocytes are also present in mild