rieties and were first classified according as, under the microscope,
they presented a granular appearance or appeared clear. The cells were
also distinguished from one another according as they possessed fine or
coarse granules. The granules are confined to the protoplasm of the
cell, and it has been shown that they differ chemically, because their
staining properties vary. Thus, some granules select an acid stain, and
the cells containing them are then designated _acidophile_ or
_eosinophile_;[1] other granules select a basic stain and are called
_basophile_, while yet others prefer a neutral stain (_neutrophile_).

In human blood the following varieties of leucocytes may be
distinguished:--

1. _The Polymorphonuclear Cell._--This possesses a nucleus of very
complicated outline and a fair amount of protoplasm filled with numbers
of fine granules which stain with eosin. They vary in size but are
usually about 0.01 mm. in diameter. They are highly amoeboid and
phagocytic, and form about 70% of the total number of leucocytes.

2. _The Coarsely Granular Eosinophile Cell._--These large cells contain
a number of well-defined granules which stain deeply with acid dyes. The
nucleus is crescentic. The cells amount to about 2% of the total number
of leucocytes, though the proportion varies considerably. They are
actively amoeboid.

3. _The Lymphocyte._--This is the smallest leucocyte, being only about
0.0065 mm. in diameter. It has a large spherical nucleus with a small
rim of clear protoplasm surrounding it. It forms from 15 to 40% of the
number of leucocytes, and is less markedly amoeboid than the other
varieties.

4. _The Hyaline_ (Gr. [Greek: hualinos], glassy, crystalline, [Greek:
ualos], glass) _cell or macrocyte_ (Gr. [Greek: makros], long or
large).--This is a cell similar to the last with a spherical, oval or
indented nucleus, but it has much more protoplasm. It constitutes about
4% of all the leucocytes and is highly amoeboid and phagocytic.

5. _The Basophile Cell_.--This possesses a spherical nucleus and the
protoplasm contains a small number of granules staining deeply with
basic dyes. It is rarely found in the blood of adults except in certain
diseases.

_Functions._--These cells act as scavengers or as destroyers of living
organisms that may have gained access to the tissue spaces. They play an
important part in the chemical processes underlying the phenomena of
immunity, and some at least are of importan