es is
known to be due to life processes of minute organisms, as is the
gangrene which follows unskilful surgery. The study of the "fauna and
flora" within living organisms has now become a science of itself,
demanding the greatest care in observation and the most complete of
appliances. "_Omne vivum ex vivo_," "all life from life," was an
aphorism of the naturalists of a century or two ago. It was to them a
new and broad generalization. It has not yet been set aside. The classic
experiments of Tyndall show that this law applies to all creatures we
have yet recognized or classified. As far as science can tell,
spontaneous generation is still a myth, having no basis in observation,
no warrant in experiment. It remains as a pure deduction from the
philosophical conception of Monism, incapable of proof, insusceptible of
refutation. The argument for it is chiefly this: Life exists on a globe
once lifeless. How did life begin? If not through spontaneous
generation, how did it come? Must it not have been by the operation of
those laws and forces which through all time change lifeless into living
matter? Very likely, but we do not know. We know nothing whatever of
such laws and forces, and we gain nothing by veiling our ignorance under
a philosophical necessity.

Moreover, if spontaneous generation occurs as a resultant of any
forces, like forces would produce it again. We have never known it to
occur. Should it occur the organisms thus produced would have no bonds
of blood-relationship with those already in existence. With these they
should show no homology, as they could have no inheritance in common.
But all known organisms have common homologies. The factors of organic
evolution are essentially the same for all. The unity of life amid all
its diversity seems to point to origin from a common stock. If not from
one stock, the lines of division between one and another are hidden from
us. The study of embryology breaks down the time-honored branch lines of
vertebrates, articulates, mollusks, and radiates. The groups of animals
are more numerous, more complex, and more intertangled than Cuvier and
Agassiz thought. The number of primary branches of animals or plants is
uncertain, their boundaries undefined.

If spontaneous generation exists, it is a factor in evolution. If it is
a factor, our explanation of the meaning and nature of homology must be
fundamentally changed. But it may be that it should be changed. We
cannot show