In the cells of plants, in addition to the cell wall, the cell body
and the cell juice require to be examined. The material of the cell
body, or the cell contents, was named by von Mohl (1846) protoplasm,
and consisted of a colorless tenacious substance which partly lined the
cell wall (primordial utricle) and partly traversed the interior of
the cell as delicate threads inclosing spaces (vacuoles) in which the
cell juice was contained. In the protoplasm the nucleus was embedded.
Nägeli, about the same time, had also recognized the difference between
the protoplasm and the other contents of vegetable cells, and had
noticed its nitrogenous composition.
Though the analogy with a closed bladder or vesicle could no longer
be sustained in the animal tissues, the name ‘cell’ continued to be
retained for descriptive purposes, and the body of the cell was spoken
of as a more or less soft substance inclosing a nucleus (Leydig). In
1861 Max Schultze adopted for the substance forming the body of the
animal cell the term ‘protoplasm.’ He defined a cell to be a particle
of protoplasm in the substance of which a nucleus was situated. He
regarded the protoplasm, as indeed had previously been pointed out by
the botanist Unger, as essentially the same as the contractile sarcode
which constitutes the body and pseudopodia of the Amœba and other
Rhizopoda. As the term ‘protoplasm,’ as well as that of ‘bioplasm’
employed by Lionel Beale in a somewhat similar though not precisely
identical sense, involves certain theoretical views of the origin and
function of the body of the cell, it would be better to apply to it the
more purely descriptive term ‘cytoplasm’ or ‘cell plasm.’
Schultze defined protoplasm as a homogeneous, glassy, tenacious
material, of a jelly-like or somewhat firmer consistency, in which
numerous minute granules were embedded. He regarded it as the part
of the cell especially endowed with vital energy, whilst the exact
function of the nucleus could not be defined. Based upon this
conception of the jelly-like character of protoplasm, the idea for a
time prevailed that a structureless, dimly granular, jelly or slime
destitute of organization, possessed great physiological activity, and
was the medium through which the phenomena of life were displayed.
More accurate conceptions of the nature of the cell plasm soon began
to be entertained. Brücke recognized that the body of the cell was
not simple, but had a complex organization. Hemming observed that the
cell plasm contained extremely delicate threads, which frequently
formed a network, the interspaces of which were occupied by a more
homogeneous substance. Where the threads crossed each other, granular
particles (milkrosomen) were situated. Bütschli considered that he
could recognize in the cell plasm a honeycomb-like appearance, as if
it consisted of excessively minute chambers in which a homogeneous
more or less fluid material was contained. The polar and spindle-like
radiations visible during the process of karyokinesis, which have
already been referred to, and the presence of the centrosome, possibly
even during the resting stage of the cell, furnished additional
illustrations of differentiation within the cell plasm. In many cells
there appears also to be a difference in the character of the cell
plasm which immediately surrounds the nucleus and that which lies at
and near the periphery of the cell. The peripheral part (ektoplasma)
is more compact and gives a definite outline to the cell, although
not necessarily differentiating into a cell membrane. The inner part
(endoplasma) is softer and is distinguished by a more distinct granular
appearance and by containing the products specially formed in each
particular kind of cell during the nutritive process.
By the researches of numerous investigators on the internal
organization of cells in plants and animals, a large body of evidence
has now been accumulated, which shows that both the nucleus and the
cell plasm consist of something more than a homogeneous, more or less
viscid, slimy material. Recognizable objects in the form of granules,
threads, or fibers can be distinguished in each. The cell plasm and
the nucleus respectively are therefore not of the same constitution
throughout, but possess polymorphic characters, the study of which in
health and the changes produced by disease will for many years to come
form important matters for investigation.
(To be concluded.)