nds. There now suddenly appears an endeavour to bring all the white
blood corpuscles into one class, and to regard the different forms as
different stages merely of the same kind of cells. The following
sections will show that this tendency is unwarranted and unpractical.

I. NORMAL AND PATHOLOGICAL HISTOLOGY OF THE WHITE BLOOD CORPUSCLES.

The classification of the white corpuscles of normal human blood, drawn
up by Ehrlich, has been accepted by most authors, and we therefore give
a short summary of it, as founded on the dry specimen.

1. =The Lymphocytes.= These are small cells, as a rule approximating in
size to the red blood corpuscles. Their body is occupied by a large
round homogeneously stained nucleus centrally situated, whilst the
protoplasm surrounds the nucleus as a concentric border. Between nucleus
and protoplasm there is often found a narrow areola, which doubtless
results from artificial retraction. Nucleus and protoplasm are basophil,
nevertheless in many methods of staining the protoplasm possesses a much
stronger affinity for the basic stain than does the nucleus. The nucleus
in these cases stands out as a bright spot from the deeply stained mass
of protoplasm, which is reticulated in a peculiar manner.

Within the nucleus are often to be found one or two nucleoli with a
relatively thick and deeply stained membrane. With methylene blue and
similar dyes the protoplasm stains unequally, which is not to be
considered as the expression of a granulation, as Ehrlich first
assumed, but rather of a reticular structure. The contour of the
lymphocytes is not quite smooth as a rule, at least in the larger forms,
but is somewhat frayed, jagged, and uneven (Fig. 1). Small portions of
the peripheral substance may repeatedly bud off, especially in the large
forms, and circulate in the blood as free elements. In stained
specimens, especially from lymphatic leukaemia, these forms, which
completely resemble the protoplasm of the lymphocytes in their staining,
may from their nature and origin be readily recognised.

As far as the further metamorphosis of the nucleus is concerned, a sharp
notching of the border of the nucleus may occasionally be found, the
further fate of which is shewn in the accompanying figure (Fig. 3). It
is evident that in this case the resulting nuclear forms are quite
different from those which are characteristic of the polynuclear
elements.

The protoplasm possesses no special affinity for