sary to
life in itself, hence they enter as food and become transformed into
protoplasm. The lowest forms of life with which we are acquainted are
nothing but simple pieces of protoplasm and yet they have all the
appearance of living objects.

But in what consist these signs of life which are common to all living
objects? In this, that the protoplasm takes from its surroundings
other matter suitable to itself and assimilates it while other former
portions of the body become decomposed and are thrown off. Other
things, not living bodies, decompose or make combinations, but cease
thereby to be what they were. The rock worn by atmospheric action is
no longer rock, the metal which becomes oxidised goes off in rust. But
what causes the destruction of dead bodies is the essential of the
existence of living protoplasm. From the very moment when the unbroken
interchange in the constituents of protoplasm ceases, the continual
interchange of receiving and throwing off, from that moment the
protoplasmic substance itself ceases, becomes decomposed, that is,
dies.

Life, the mode of existence of protoplasmic substance, therefore
consists in this, that at one and the same moment it is itself and
something else, and this is not the result of a process to which it is
compelled by external agency, since this may happen also with objects
which are dead. On the contrary life, which is change of matter, is
consequent upon nourishment and throwing off, is a self-fulfilling
process inherent in its medium, protoplasm, without which it cannot
exist. Hence, it follows that if chemistry should ever discover how to
make protoplasm artificially, this protoplasm must show some signs of
life, even if very insignificant. It is, of course, doubtful if
chemistry will discover the proper food for this protoplasm at the
same time as the protoplasm.

Through the changes in matter produced by nourishment and throwing
off, as actual functions of the protoplasm, and through its own
plasticity, proceed all the other most simple factors of life,
sensibility which consists in the interchange between the protoplasm
and its food, contractibility which shows itself at a very low stage
in the consumption of food, possibility of growth which is shown in
the lowest stages of development by splitting, and internal motion
without which neither the consumption nor assimilation of food is
possible.

Our definition of life is, of course, very incomplete since in ord