eus, which had been thought of as an organ of reproduction. These
suggestions appeared indefinitely in the writings of one scientist and
another, and were finally formulated in 1860 into a general theory which
formed what has sometimes been called the starting point of modern
biology. From that time the material known as _protoplasm_ was elevated
into a prominent position in the discussion of all subjects connected
with living phenomena. The idea of protoplasm was first clearly defined
by Schultze, who claimed that the real active part of the cell was the
cell substance within the cell wall. This substance he proved to be
endowed with powers of motion and powers of inducing chemical changes
associated with vital phenomena. He showed it to be the most abundant in
the most active cells, becoming less abundant as the cells lose their
activity, and disappearing when the cells lose their vitality. This cell
substance was soon raised into a position of such importance that the
smaller body within it was obscured, and for some twenty years more the
nucleus was silently ignored in biological discussion. According to
Schultze, the cell substance itself constituted the cell, the other
parts being entirely subordinate, and indeed frequently absent. A cell
was thus a bit of protoplasm, and nothing more. But the more important
feature of this doctrine was not the simple conclusion that the cell
substance constitutes the cell, but the more sweeping conclusion that
this cell substance is in _all_ cells essentially _identical._ The study
of all animals, high and low, showed all active cells filled with a
similar material, and more important still, the study of plant cells
disclosed a material strikingly similar. Schultze experimented with this
material by all means at his command, and finding that the cell
substance in all animals and plants obeys the same tests, reached the
conclusion that the cell substance in animals and plants is always
identical. To this material he now gave the name protoplasm, choosing a
name hitherto given to the cell contents of plant cells. From this time
forth this term protoplasm was applied to the living material found in
all cells, and became at once the most important factor in the
discussion of biological problems.

The importance of this newly formulated doctrine it is difficult to
appreciate. Here, in protoplasm had been apparently found the foundation
of living phenomena. Here was a substance universa