PROTOPLASM, defined by Huxley as "the physical basis of life," is the essential material of which living creatures are corn posed. A typical multicellular organism can be analysed into component organs, which are built up of diverse tissues, in turn consisting of cells. In pursuing the analysis the biologist reaches, within the cell, the essential living matter or protoplasm. But a cell often includes material which cannot be thought of as alive, or as playing an essential role in the characteristic chemical routine or metabolism. Such non-living material is conveniently called metaplasm, and may be illustrated by waste pigments or by crystals. If the whole of this metaplasm could be subtracted from the entire cell-substance or cytoplasm, and from the whole nuclear substance or nucleoplasm, the remainder would be proto plasm.
Soon after the vague recognition of the cellular structure of plants and animals in the later i 7th century by Hooke, Malpighi and Grew, there began to be some appreciation of the fact that the cells had contents. Yet it required another century before Corti and Treviranus saw the streaming movements inside the cells of some plants. Even then the open secret was missed, for the objective envisaging of life as involving an intricate series of physical and chemical changes within the cells was still far distant.
The term "protoplasm" was first used by Purkinje in 1840 in reference to the formative material of animal embryos. It was taken over by von Mohl (1846) and applied to the "slimy, granu lar, semifluid" constituents of plant-cells, as distinguished from cell-wall, cell-sap and nucleus. Some time before that, however, Dujardin had discerned the living material in Foraminifera. He called this "sarcode" (1835), and defined it as a "living jelly, glutinous and transparent, insoluble in water, and capable ol contracting into globular masses and of adhering to dissecting needles so that it can be drawn out like mucus." Soon there came an identification of Dujardin's animal "sarcode" and von Mohl's plant "protoplasm," and yet the acceptance of this unifying idea was slow. This was partly because the statement of the cell
theory by Schwann and Schleiden (1838) gave undue prominence to the importance of the cell-wall. Indeed it was not till 1861 that Max Schultze won conviction for the fundamental idea that throughout the whole world of life there is one general kind of living material, protean, yet nevertheless always essentially similar. ( J. A. TH.) The various methods of studying living matter may be grouped under three general headings : ) microscopic tions of the structure and behaviour of the great variety of cells which constitute living organisms, both plant and animal; (2) a chemical analysis of the materials composing protoplasm and (3) the application of experimental methods on living cells to ascertain the extent to which protoplasmic phenomena can be explained in physico-chemical terms and to study chemical reactions within the living cell. All of these methods have been used since proto plasm was first recognized as the physical basis of life. However, the results obtained were largely empirical or purely speculative until the newer developments in the fields of physics and chemistry could give some significance to the physical configuration and chemical constitution of protoplasm.
The technical difficulties of making observational studies on cellular structures in the living state have resulted in the elabora tion of methods for the fixation of tissues and cells with killing agents. As for chemical analyses of cellular tissues the usual procedure entails complete destruction of the cell. The results obtained by such methods can be accepted only with the qualifica tion that the passage from life to death undoubtedly occasions structural and chemical changes in the form of recombinations and decompositions so that the structures and compounds found in dead matter can offer at best a very incomplete idea of the compo sition of living protoplasm.