he
investigation of the constitution of matter; we have now to talk of its
researches into the nature of Life.

The discovery that all plant and animal life is developed from living
cells was made, as we have already stated, more than seventy years ago.
Since then our knowledge of the formation and history of these cells
has been continually growing. The size of cells varies, but as a rule
they are very minute. They consist of what is termed protoplasm. At
one time it was supposed that protoplasm was structureless. Now it is
known that the protoplasmic cell contains a nucleus and a surrounding
body. Moreover, the nucleus, or small spot in the centre, has within
it a spiral structure of a very complicated kind. Every cell is
derived from a pre-existing cell by a process of division, the two
resulting cells being apparently identical with the parent cell. {77}
The cells possess the power of assimilating other cells or fragments of
cells. As they grow they move and go in search of food and light and
air and moisture. They exhibit feeling, and shrink as if in pain.
Spots specially sensitive to vibrations become eyes and ears; and thus
the various organs and faculties are evolved under the stimulating
influence of environment. The progress, so far as it is physical, can
be traced from the lowest blue-green algae right up to man. And all
throughout, in so far as their chemical composition is concerned, the
constituent elements of the living structure are the same. It is said
to be practically impossible to distinguish between the cells of a
toadstool and those of a human being.

But when all this has been explained, we have still left one great
question unanswered. How is the protoplasm made? Is there any
connexion of development to be traced whereby life can be shewn to have
arisen from inorganic matter? Protoplasm, under analysis, is found to
consist of some of the commonest elements on the earth's surface, such
as carbon, hydrogen, oxygen, nitrogen, and phosphorus. Apart from its
very complicated structure, its contents are not hard to provide. And
we know that there was a time when it must of necessity have been
formed out of that which was not living, {78} for there was a time when
our globe was in a state of incandescent heat in which no life that we
know could possibly have existed. More than this we cannot say. Sir
William Thomson, as President of the British Association in 1871,
suggested that a