undergoes a development which we know as its individual life and
which, so far as its physical substance is concerned, ends with death.
Death is the destruction of the greater part of this individual
organism which, when death ensues, once more becomes lifeless matter.
Only small portions of this matter, the germ cells, continue to live
under certain conditions which nature has fixed.
The germ cell--as has been established by the microscope--is the tiny
cell which in the lowest living organisms as well as in man himself,
forms the unit of physical development. Yet even this tiny cell is
already a highly organized and perfected thing. It is composed of the
most widely differing elements which, taken together, form the
so-called protoplasm or cellular substance. And for all life
established in nature the cell remains the constant and unchanging
form element. It comprises the cell-protoplasm and a nucleus imbedded
in it whose substance is known as the nucleoplasm. The nucleus is the
more important of the two and, so to say, governs the life of the
cell-protoplasm.
The lower one-celled organisms in nature increase by division, just as
do the individual cells of a more highly organized, many-celled order
of living beings. And in all cases, though death or destruction of the
cells is synonymous with the death or destruction of the living
organism, the latter in most cases already has recreated itself by
reproduction.
We will not go into the very complicated details of the actual process
of the growth and division of the protoplasmic cells. It is enough to
say that in the case of living creatures provided with more
complicated organisms, such as the higher plants, animals and man, the
little cell units divide and grow as they do in the case of the lower
organisms. The fact is one which shows the intimate inner relationship
of all living beings.
THE LADDER OF ORGANIC ASCENT
As we mount the ascending ladder of plant and animal life the
unit-cell of the lower organisms is replaced by a great number of
individual cells, which have grown together to form a completed whole.
In this complete whole the cells, in accordance with the specific
purpose for which they are intended, all have a different form and a
different chemical composition. Thus it is that in the case of the
plants leaves, flowers, buds, bark, branches and stems are formed, and
in that of animals skin, intestines, glands, blood, muscles, nerves,
brain and the organs of sense. In spite of the complicated nature of