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STRUCTURE OF CELLS. 523
direction of this indwelling principle just as plainly as we see the blue
tint of the water ; and we feel as sure that there is a force outside the
properties of matter, which pervades and vivifies every living particle,
as we do of the grain of copper left after the evaporation of its men-
struum. It is only as man contemplates, at the same time, matter and
mind that he is able to master the first data of life-science or form even
a dim conception of that Infinite Spirit " whom none by searching can
find out."
But we must now leave the question of how life begins, and consider
life as it presents itself to our eyes when seen in its minutest forms and
at its earliest known stage of existence i. e. as an aggregation of trans-
parent cells.
The unit of life, as we are able to demonstrate, is expressed in small
bodies denominated cells, and " the life-history of the hidividual cell is
the first important and indispensable basis whereon to found the true
physiology of the life-history of all the orders of creation." We shall
therefore take our starting-point from the simple cell, which is the same,
in respect to its chief characters, in animal and vegetable life.
Structure of Cells.
A mature cell is composed of a nucleus, a cell-body, and a cell-limit,
or wall. The nucleus is that part of the cell which is first formed from
the germinal matter, and is the first to be affected when a change in form
occurs. The nucleus may assume various shapes, as round, oval, rod-
like, or irregular. It generally encloses central dots, termed nucleoli,
which are thought by some histologists to be the enlargements of por-
tions of an irregular network of fibres which can be seen inside the
nucleus. The cell-body is the formed material which surrounds the
nucleus. The cell-wall is the limit of this formed material. When we
speak of a cell-wall, we do not mean that there is any abrupt demarca-
tion between the cell-body and its outer edge ; the one passes gradually
into the other. Cells draw their nourishment from a protoplasmic sub-
stance which circulates in the intercellular spaces. This supply of cell-
pabulum is inert until acted upon by the living principle resident in the
cell. Such are the visible parts of a cell when seen in its early stage of
existence.
Ziegler, speaking of the youngest embryonal cells, says : " The cell
by itself appears originally as a microscopic mass of pale, slimy, finely-
granular matter—the so-called protoplasm. It usually contains within
it a nucleus—that is to say, a structure like a tiny vesicle, whose
form may be round, oval, rod-like, or irregular, and in whose interior
we can make out, by proper handling— 1, small definite bodies, the
nucleus-corpuscles ; 2, a net-like framework of nucleus substance ; and,
3, a clear fluid, the nucleus juice. The young cell is at first naked.
Only in its raaturer stages does it develop on its surface an oj^tically
distinct membrane or other structure according to the special tissue
of which it forms a part." This accords with my own observation.
For example, in studying sections from the mucous membrane of the
mouth it is found that the deepest part of the epithelial layer of the
STRUCTURE OF CELLS. 523
direction of this indwelling principle just as plainly as we see the blue
tint of the water ; and we feel as sure that there is a force outside the
properties of matter, which pervades and vivifies every living particle,
as we do of the grain of copper left after the evaporation of its men-
struum. It is only as man contemplates, at the same time, matter and
mind that he is able to master the first data of life-science or form even
a dim conception of that Infinite Spirit " whom none by searching can
find out."
But we must now leave the question of how life begins, and consider
life as it presents itself to our eyes when seen in its minutest forms and
at its earliest known stage of existence i. e. as an aggregation of trans-
parent cells.
The unit of life, as we are able to demonstrate, is expressed in small
bodies denominated cells, and " the life-history of the hidividual cell is
the first important and indispensable basis whereon to found the true
physiology of the life-history of all the orders of creation." We shall
therefore take our starting-point from the simple cell, which is the same,
in respect to its chief characters, in animal and vegetable life.
Structure of Cells.
A mature cell is composed of a nucleus, a cell-body, and a cell-limit,
or wall. The nucleus is that part of the cell which is first formed from
the germinal matter, and is the first to be affected when a change in form
occurs. The nucleus may assume various shapes, as round, oval, rod-
like, or irregular. It generally encloses central dots, termed nucleoli,
which are thought by some histologists to be the enlargements of por-
tions of an irregular network of fibres which can be seen inside the
nucleus. The cell-body is the formed material which surrounds the
nucleus. The cell-wall is the limit of this formed material. When we
speak of a cell-wall, we do not mean that there is any abrupt demarca-
tion between the cell-body and its outer edge ; the one passes gradually
into the other. Cells draw their nourishment from a protoplasmic sub-
stance which circulates in the intercellular spaces. This supply of cell-
pabulum is inert until acted upon by the living principle resident in the
cell. Such are the visible parts of a cell when seen in its early stage of
existence.
Ziegler, speaking of the youngest embryonal cells, says : " The cell
by itself appears originally as a microscopic mass of pale, slimy, finely-
granular matter—the so-called protoplasm. It usually contains within
it a nucleus—that is to say, a structure like a tiny vesicle, whose
form may be round, oval, rod-like, or irregular, and in whose interior
we can make out, by proper handling— 1, small definite bodies, the
nucleus-corpuscles ; 2, a net-like framework of nucleus substance ; and,
3, a clear fluid, the nucleus juice. The young cell is at first naked.
Only in its raaturer stages does it develop on its surface an oj^tically
distinct membrane or other structure according to the special tissue
of which it forms a part." This accords with my own observation.
For example, in studying sections from the mucous membrane of the
mouth it is found that the deepest part of the epithelial layer of the
