eparated from the
lymphocytes because they are totally different in appearance, and
because forms transitional between the two are not observed. It cannot
yet be decided from which blood-producing organs these forms arise,
whether from spleen or bone-marrow, although there are many reasons for
regarding the latter as their place of origin.

These large mononuclear leucocytes change in the blood to the following
kind:

3. "=The transitional forms.=" These resemble the preceding, but are
distinguished therefrom by deep notchings of the nucleus, which often
give it an hour-glass shape, further by a somewhat greater affinity of
the nucleus for stains, and by the presence of scanty neutrophil
granulations in the protoplasm. The groups 2 and 3 comprise together
about 2-4% of the white blood corpuscles[11].

4. The (so-called) "=polynuclear leucocytes=." These arise in small part,
as will be described later in detail, from the above-mentioned No. 3,
within the blood stream. By far the larger part is produced fully formed
in the bone-marrow, and emigrate to the blood. These cells are rather
smaller than Nos. 3 and 2 and are distinguished by the following
peculiarities: firstly by a peculiar polymorphous form of nucleus which
gives the relatively long, irregularly bulged and indented nuclear rod
the appearance of an S, Y, E or Z. The complete decomposition of this
nuclear rod into three to four small round single nuclei may occur
during life, as a natural process. Ehrlich first discovered it in a case
of haemorrhagic small-pox; it is frequently found in fresh exudations.
Formerly when various reagents, for instance acetic acid, were
customarily used, the decomposition of the nucleus into several parts
was more frequently observed, and Ehrlich for this reason chose the not
wholly appropriate name "polynuclear" for this form of cell. As this
name has now been universally adopted, and misunderstandings cannot be
expected, it is undoubtedly better to keep to it. The expression "Cells
with polymorphous nuclei" would be more accurate.

[Illustration: Fig. 3.

Nucleoli in larger lymphocytes.

(From a photograph of a preparation from chronic lymphatic leukaemia.)

_To face page 74_]

The nucleus stains very deeply with all dyes; the protoplasm possesses a
strong attraction for most acid stains, and is unmistakeably
characterised by the presence of a dense neutrophil granulation. The
reaction of the protoplasm is alkaline, to a