The properties of living matter.
1. Its _chemical composition_--containing, as it invariably does, one or
more forms of a complex compound of carbon, hydrogen, oxygen and
nitrogen, the so-called protein or albumin (which has never yet been
obtained except as a product of living bodies), united with a large
proportion of water, and forming the chief constituent of a substance
which, in its primary unmodified state, is known as _protoplasm_.
2. Its _universal disintegration and waste by oxidation; and its
concomitant reintegration by the intussusception of new matter_.
A process of waste resulting from the decomposition of the molecules of
the protoplasm, in virtue of which they break up into more highly
oxidated products, which cease to form any part of the living body, is a
constant concomitant of life. There is reason to believe that carbonic
acid is always one of these waste products, while the others contain the
remainder of the carbon, the nitrogen, the hydrogen and the other
elements which may enter into the composition of the protoplasm.
The new matter taken in to make good this constant loss is either a
ready-formed protoplasmic material, supplied by some other living being,
or it consists of the elements of protoplasm, united together in simpler
combinations, which consequently have to be built up into protoplasm by
the agency of the living matter itself. In either case, the addition of
molecules to those which already existed takes place, not at the surface
of the living mass, but by interposition between the existing molecules
of the latter. If the processes of disintegration and of reconstruction
which characterize life balance one another, the size of the mass of
living matter remains stationary, while, if the reconstructive process
is the more rapid, the living body _grows_. But the increase of size
which constitutes growth is the result of a process of molecular
intussusception, and therefore differs altogether from the process of
growth by accretion, which may be observed in crystals and is effected
purely by the external addition of new matter--so that, in the
well-known aphorism of Linnaeus, the word "grow" as applied to stones
signifies a totally different process from what is called "growth" in
plants and animals.