form, as may be seen in Figs. 3 and 5. The typical cell is usually
_globular_ in form, other shapes being the result of pressure or of
similar modifying influences. The globular, as well as the large, flat
cells, are well shown in a drop of saliva. Then there are the _columnar_
cells, found in various parts of the intestines, in which they are closely
arranged side by side. These cells sometimes have on the free surface
delicate prolongations called cilia. Under the microscope they resemble a
wave, as when the wind blows over a field of grain (Fig. 5). There are
besides cells known as _spindle, stellate, squamous_ or pavement, and
various other names suggested by their shapes. Cells are also described as
to their contents. Thus _fat_ and _pigment_ cells are alluded to in
succeeding sections. Again, they may be described as to their functions or
location or the tissue in which they are found, as _epithelial_ cells,
_blood_ cells (corpuscles, Figs. 2 and 66), _nerve_ cells (Fig. 4), and
_connective-tissue_ cells.

14. Vital Properties of Cells. Each cell has a life of its own. It
manifests its vital properties in that it is born, grows, multiplies,
decays, and at last dies.[3] During its life it assimilates food, works,
rests, and is capable of spontaneous motion and frequently of locomotion.
The cell can secrete and excrete substance, and, in brief, presents nearly
all the phenomena of a human being.

Cells are produced only from cells by a process of self-division,
consisting of a cleavage of the whole cell into parts, each of which
becomes a separate and independent organism. Cells rapidly increase in
size up to a certain definite point which they maintain during adult life.
A most interesting quality of cell life is motion, a beautiful form of
which is found in ciliated epithelium. Cells may move actively and
passively. In the blood the cells are swept along by the current, but the