endeavoured to put the question to
an experimental test. He said to himself, If these infusorial animalcules
come from germs, their germs must exist either in the substance infused,
or in the water with which the infusion is made, or in the superjacent
air. Now the vitality of all germs is destroyed by heat. Therefore, if I
boil the infusion, cork it up carefully, cementing the cork over with
mastic, and then heat the whole vessel by heaping hot ashes over it, I
must needs kill whatever germs are present. Consequently, if Redi's
hypothesis hold good, when the infusion is taken away and allowed to
cool, no animalcules ought to be developed in it; whereas, if the
animalcules are not dependent on pre-existing germs, but are generated
from the infused substance, they ought, by and by, to make their
appearance. Needham found that, under the circumstances in which he made
his experiments, animalcules always did arise in the infusions, when a
sufficient time had elapsed to allow for their development.

In much of his work Needham was associated with Buffon, and the results
of their experiments fitted in admirably with the great French
naturalist's hypothesis of "organic molecules," according to which, life
is the indefeasible property of certain indestructible molecules of
matter, which exist in all living things, and have inherent activities by
which they are distinguished from not living matter. Each individual
living organism is formed by their temporary combination. They stand to
it in the relation of the particles of water to a cascade, or a
whirlpool; or to a mould, into which the water is poured. The form of the
organism is thus determined by the reaction between external conditions
and the inherent activities of the organic molecules of which it is
composed; and, as the stoppage of a whirlpool destroys nothing but a
form, and leaves the molecules of the water, with all their inherent
activities intact, so what we call the death and putrefaction of an
animal, or of a plant, is merely the breaking up of the form, or manner
of association, of its constituent organic molecules, which are then set
free as infusorial animalcules.

It will be perceived that this doctrine is by no means identical with
_Abiogenesis_, with which it is often confounded. On this hypothesis, a
piece of beef, or a handful of hay, is dead only in a limited sense. The
beef is dead ox, and the hay is dead grass; but the "organic molecules"
of the beef