was
something quite different from sap. He asserted that the nucleus of the
cell lies within this substance and not attached to the cell wall as
Schleiden had contended. He saw, too, that the chlorophyl granules,
and all other of the cell contents, are incorporated with the "opaque,
viscid fluid," and in 1846 he had become so impressed with the
importance of this universal cell substance that he gave it the name
of protoplasm. Yet in so doing he had no intention of subordinating the
cell wall. The fact that Payen, in 1844, had demonstrated that the
cell walls of all vegetables, high or low, are composed largely of one
substance, cellulose, tended to strengthen the position of the cell wall
as the really essential structure, of which the protoplasmic contents
were only subsidiary products.

Meantime, however, the students of animal histology were more and more
impressed with the seeming preponderance of cell contents over cell
walls in the tissues they studied. They, too, found the cell to be
filled with a viscid, slimy fluid capable of motion. To this Dujardin
gave the name of sarcode. Presently it came to be known, through the
labors of Kolliker, Nageli, Bischoff, and various others, that there are
numerous lower forms of animal life which seem to be composed of this
sarcode, without any cell wall whatever. The same thing seemed to be
true of certain cells of higher organisms, as the blood corpuscles.
Particularly in the case of cells that change their shape markedly,
moving about in consequence of the streaming of their sarcode, did it
seem certain that no cell wall is present, or that, if present, its role
must be insignificant.

And so histologists came to question whether, after all, the cell
contents rather than the enclosing wall must not be the really essential
structure, and the weight of increasing observations finally left no
escape from the conclusion that such is really the case. But attention
being thus focalized on the cell contents, it was at once apparent
that there is a far closer similarity between the ultimate particles of
vegetables and those of animals than had been supposed. Cellulose and
animal membrane being now regarded as more by-products, the way was
clear for the recognition of the fact that vegetable protoplasm and
animal sarcode are marvellously similar in appearance and general
properties. The closer the observation the more striking seemed this
similarity; and finally, about 1860, it w