fe has made its
appearance under observation, except from antecedent life.

But, to exclude all trace of antecedent life, it is necessary not only
to shut out floating germs, but to kill all germs previously existing
in the material we are dealing with. This killing of previous life is
usually accomplished by heat; but it has been argued that strong heat
will destroy not only the life but the potentiality for life, will
break up the complex aggregate on which life depends, will deprive the
incubating solution not only of life but of livelihood. There is some
force in the objection, and it is an illustration of the difficulty
surrounding the subject. But Tyndall showed that antecedent life could
be destroyed, without any very high temperature, by gentle heat
periodically applied: heat insufficient to kill the germs, but
sufficient to kill the hatched or developed organisms. Periodic heating
enables the germs of successive ages to hatch, so to speak, and the
product to be slain; and, although some each time may have reproduced
germs before slaughter--eggs capable of standing the warmth--yet a
succession of such warmings would ultimately be fatal to all, and that
without necessarily breaking up the protoplasmic complex aggregates on
the existence of which the whole vital potentiality depends.

So far, however, all effort at spontaneous generation has been a
failure; possibly because some essential ingredient or condition was
omitted, possibly because great lapse of time was necessary. But
suppose it was successful; what then? We should then be reproducing in
the laboratory a process that must at some past age have occurred on
the earth; for at one time the earth was certainly hot and molten and
inorganic, whereas now it swarms with life.

Does that show that the earth generated the life? By no means; no more
than it need necessarily have generated all the gases of its
atmosphere, or the meteoric dust which lies upon its snows.

Life may be something not only ultra-terrestrial, but even immaterial,
something outside our present categories of matter and energy; as real
as they are, but different, and utilising them for its own purpose.
What is certain is that life possesses the power of vitalising the
complex material aggregates which exist on this planet, and of
utilising their energies for a time to display itself amid terrestrial
surroundings; and then it seems to disappear or evaporate whence it
came. It is perpetual