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 amoeba 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, amoebÆ, 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an investing membrane, has the power of extension in any direction in the form of temporary processes capable of being withdrawn again; and it has also the characteristic property of streaming in minute masses through closed membranes without the loss of the identity of such masses.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 Amoeba.”