ifestations, which from Aristotle onwards have been subjected
to a scrutiny similar to that which has been given to the physical facts
of the universe and with results in many points similar also. But the
facts, although superficially more familiar, are infinitely more
complicated, and the scrutiny has only commenced in earnest some hundred
years ago. Considering the short space for this concentrated and
systematic study, the results are at least as wonderful as those
achieved by the physicists. Two or three points of suggestive analogy
between the courses of the two great branches of science may here be
mentioned.

We will put first the fundamental question on which, as we have seen, no
final answer has yet been reached: What is life, and is there any
evidence of life arising from the non-living? Now this baffling and
probably unanswerable question--unanswerable, that is, in terms which go
beyond the physical concomitants of life--has played the part in biology
which the alchemists' quest played in chemistry. It led by the way to a
host of positive discoveries. Aristotle, the father of biology, believed
in spontaneous generation. He was puzzled by the case of parasites,
especially in putrefying matter. Even Harvey, who made the first great
definite discovery about the mechanism of the body, agreed with
Aristotle in this error. It was left for the minute and careful
inquirers of the nineteenth century to dispose of the myth. It was only
after centuries of inquiry that the truth was established that life, as
we know it, only arises from life. But the whole course of the inquiry
had illuminated the nature of life and had brought together facts as to
living things of all kinds, plants and animals, great and small, which
show superficially the widest difference. Illumination by unification is
here the note, as clearly as in the mathematical-physical sciences. All
living things are found to be built up from cells and each cell to be an
organism, a being, that is, with certain qualities belonging to it as a
whole, which cannot be predicated of any collection of parts not an
organism. The cell is such an organism, just as the animal is an
organism, and among its qualities as an organism is the power of growth
by assimilating material different from itself. Yet, in spite of this
assimilation and constant change, it grows and decays as one whole and
reproduces its like.

Another point of analogy between the animate and the inan