lly present in animals
and plants, simple and uniform--a substance always present in living
parts and disappearing with death. It was the simplest thing that had
life, and indeed the only thing that had life, for there is no life
outside of cells and protoplasm. But simple as it was it had all the
fundamental properties of living things--irritability, contractibility,
assimilation, and reproduction. It was a compound which seemingly
deserved the name of "_physical basis of life_", which was soon given to
it by Huxley. With this conception of protoplasm as the physical basis
of life the problems connected with the study of life became more
simplified. In order to study the nature of life it was no longer
necessary to study the confusing mass of complex organs disclosed to us
by animals and plants, or even the somewhat less confusing structures
shown by individual cells. Even the simple cell has several separate
parts capable of undergoing great modifications in different types of
animals. This confusion now appeared to vanish, for only _one_ thing was
found to be alive, and that was apparently very simple. But that
substance exhibited all the properties of life. It moved, it could grow,
and reproduce itself, so that it was necessary only to explain this
substance and life would be explained.

(b) _Nature of Protoplasm_.--What is this material, protoplasm? As
disclosed by the early microscope it appeared to be nothing more than a
simple mass of jelly, usually transparent, more or less consistent,
sometimes being quite fluid, and at others more solid. Structure it
appeared to have none. Its chief peculiarity, so far as physical
characters were concerned, was a wonderful and never-ceasing activity.
This jellylike material appeared to be endowed with wonderful powers,
and yet neither physical nor microscopical study revealed at first
anything more than a uniform homogeneous mass of jelly. Chemical study
of the same substance was of no less interest than the microscopical
study. Of course it was no easy matter to collect this protoplasm in
sufficient quantity and pure enough to make a careful analysis. The
difficulties were in time, however, overcome, and chemical study showed
protoplasm to be a proteid, related to other proteids like albumen, but
one which was more complex than any other known. It was for a long time
looked upon by many as a single definite chemical compound, and attempts
were made to determine its chemical