Protoplasm is an albuminoid substance, ordinarily resembling the white
of an egg, consisting of carbon, oxygen, nitrogen, and hydrogen in
extremely complex and unstable molecular combination, and capable,
under proper conditions, of manifesting certain vital phenomena, as
spontaneous motion, sensation, assimilation, and reproduction, thus
constituting the physical basis of life of all plants and animals;
sarcode. It is essential to the nature of protoplasm that the substance
consist chemically of the four elements named (with or without a trace
of some other elements); but the molecule is so highly compounded
that these elements may be present in somewhat different proportions
in different cases, so that the chemical formula is not always the
same. The name has also been somewhat loosely applied to albuminous
substances widely different in some physical properties, as density
or fluidity. Thus the hard material of so-called vegetable ivory and
the soft body of an amœba are both protoplasmic. The physiological
activities of protoplasm are manifested in its irritability, or
ready response to external stimuli, as well as its inherent capacity
of spontaneous movement and other indications of life; so that the
least particle of this substance may be observed to go through the
whole cycle of vital functions. Protoplasm builds up every vegetable
and animal fabric, it is itself devoid of discernible histological
structure. It is ordinarily colorless and transparent, or nearly
so, and of glairy or viscid semi-fluid consistency, as is well seen
in the bodies of foraminifers, amœbæ, and other of the lowest forms
of animal life. Such protoplasm (originally named sarcode) when not
confined by an investing membrane, has the power of extension in
any direction in the form of temporary processes capable of being
withdrawn again; and it has also the characteristic property of
streaming in minute masses through closed membranes without the loss
of the identity of such masses. An individuated mass of protoplasm,
generally of microscopic size with or without a nucleus and a wall,
constitutes a cell, which may be the whole body of an organism, or the
structural unit of aggregation of a multicellular animal or plant.
The ovum of any creature consists of protoplasm, and all the tissues
of the most complex living organisms result from the multiplication,
differentiation, and specialization of such protoplasmic cell-units.
The life of the organism, as a whole, consists in the continuous waste
and repair of the protoplasmic material of its cells. No animal,
however, can elaborate protoplasm directly from the chemical elements
of that substance. The manufacture of protoplasm is a function of the
vegetable kingdom. Plants make it directly from mineral compounds
and from the atmosphere under the influence of the sun’s light and
heat, thus becoming the store-house of food-stuff for the animal
kingdom.--(See Cent. Dic. 6, p. 4799.)
Hence this substance, known in Vegetable Physiology as protoplasm, but
often referred to by zoölogists as sarcode, has been appropriately
designated by Professor Huxley “the physical Basis of Life.”--(W. B.
Carpenter, _Micros_, _sec. 219_.)
For the whole living world, then, it results that the morphological
unit--the primary and fundamental form of life--is merely an
individual mass of protoplasm, in which no further structure is
discernible.--(Huxley, _Anat. Invert._, _p. 18_.)
See Spencer, _Principles Biology I_, _p. 63-67_. _Encyc. Brit. 19_, _p.
828-830_; _New Int. Encyc. 16_, _p. 471-472_. Haeckel, _Ev. Man_, pp.
36-50; “_Ovum and Amœba_.”