In a scientific sense, we only know life by its
association with living matter, which in its simplest form is known as
_protoplasm_. The latter has been termed the physical basis of life, and
so far as we know every material living thing is composed wholly of
protoplasm and of the structures which it has built up.
This grayish, viscid, slimy, semi-transparent, semi-fluid substance,
similar to the white of an egg, is the most puzzling, the most wonderful
material with which science has to deal. Chemically it is composed of
various proteids, fats, carbohydrates, etc., and these in turn of but
very few elements, all of which are common, and none of which are
peculiar to protoplasm itself. And yet its essential properties, its
mechanical as well as its chemical make-up, have baffled the resources
of our wisest men with all their retorts and microscopes and other
instruments of precision.
Protoplasm is essentially uniform and similar in appearance and
properties wherever found, whether in the tissues of the human body, in
a blade of grass, or in the green slime of a stagnant pool. And yet
probably no two samples of protoplasm are ever exactly similar in all
respects, though we may never be able to detect their precise
differences.
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