Chapter 9. Cytoplasmic Structure9.1. Historical survey of the study of cytoplasmic structureIn the previous chapters I discussed the evidence that proteins, vesicles, membranous tubules and organelles move throughout the cytoplasm. In this chapter I will discuss the structure of the cytoplasm through which they move.Remember that when the cell was discovered by Robert Hooke (1665), he could only imagine that there was a possibility of an internal structure within the walls composed of passages, valves, instruments and contrivances which would be discovered by “some diligent observer, if helped by better microscopes.”In the seventeenth and eighteenth centuries the lenses on light microscopeshad various spherical and chromatic aberrations that made it difficult to see minute detailed structures in nearly transparent objects. By the nineteenth century, the optics of microscopes were improved thanks to the introduction of achromatic lenses in the 1820s and 30s by scientists and inventors, including Giovanni Battista Amici (1818) and Joseph Jackson Lister (1830), the father of the surgeon who pioneered the use of antiseptics. The newly-developed lenses were corrected for spherical and chromatic aberrations, and allowed light microscopists such as Félix Dujardin (1835,1841) to resolve objects that were less than 1 m; about one hundred times smaller than that resolvable by the naked eye (Claude, 1948; Bradbury, 1967). The new microscopes with achromatic lenses provided the means to explore the structure of living beings at the subcellular level. Dujardin (1835,1841) could now study the transparent, water-insoluble, glutinous, contractile substance that held together the food vacuoles of ciliates, and gave it the name, sarcode, from the Greek word for flesh. In 1840, Jan Purkinji used the term protoplasm, a term long used in religious contexts to mean the first created thing (Protoplast = Adam and Protoplasmator = God), to designate the living substance of animal embryos; and in 1846, Hugo von Mohl independently applied the term, protoplasm to the living substance of plant cells, since he believed that the protoplasm was capable of giving rise to all other parts of thecell. By 1848, Alexander Ecker suggested that the sarcode is a fundamental substance of all animal life, from the cells of Hydra, to those of muscles in 289higher animals, and Ferdinand Cohn (1853) further emphasized the ubiquity, constancy and importance of protoplasm when he wrote; “All these properties, however, are possessed by that substance in the plant-cell, which must be regarded as the prime seat of almost all vital activity, but especially ofall the motile phenomena in its interior--the protoplasm. Not only do its optical, chemical and physical relations coincide with those of the ‘Sarcode’ or contractile substance, but it also possesses the faculty of forming ‘vacuoles,’ ...From these considerations it would therefore appear...that the protoplasm of the Botanists, and the contractile substance and sarcode of the Zoologists, if not identical, are at all events in the highest degree analogous formations.”Calling attention to the similarity of the living substance of all cells and giving it a common name, protoplasm, propelled the search to find a definite structure within the protoplasm that would prove to be the essence of life itself (Beale, 1872; Drysdale, 1874; Brücke, 1898). All the solutions to the problems of life were to be found in the identification of this one structure. The search ensued and dualistic theories, which distinguished between the living part of the cell and the lifeless part, were all the rage. Realizing that animal cells lacked the thick extracellular matrix typically found on the exterior of plant cells, Max Schultze (1863) decided that the extracellular matrix could be eliminated as a possible candidate. This left the naked protoplasm, as the part of the cell that was endowed with all the attributes of life. The nineteenth century biologists were interested in dissecting the protoplasm down to the ultimate constituent of life. Schleiden was enamouredwith the idea that the nucleus, or the cytoblast as he called it, was the elementary particle of life. This was because he could see that cells that had a nucleus were able to reproduce, while those without one could not. Since the cytoblast was not always easy to see, Schleiden later believed that the cytoblast was an elaboration of the invisible cytoblastema, the true elementarysubstance (Schleiden, 1853). Later work showed that the nucleus existed in all living cells, divided prior to cell division, and as a consequence of its continuity, must house the living substance (von Mohl, 1852; Wilson, 1925; Goebel, 1926). Kölliker coined the term cytoplasm in 1862 to distinguish the nucleus from everything else in the protoplasm. The nucleus, like the protoplasm showed substructure, and, of course, one part was thought to be more vital than its counterpart. For example the idiochromatin was considered290to be the portion of the nucleus that contained the hereditary material, and wasthus more vital than the trophochromatin, which served merely to nourish the idiochromatin (Wilson, 1925). While one school believed the nucleus or some of its contents was the trueliving substance, others felt that the surrounding elements in the cytoplasm were more vital. Thus the cytoplasm was differentiated into various parts to distinguish the most vital part. For example, the cytoplasm was divided into the inner region of granular matter, known as the endoplasm (Pringsheim, 1854; Hofmeister, 1867) and the outer border of a clearer substance called theectoplasm. Hanstein (1868) distinguished the protoplasm from the metaplasm,where the metaplasm performed certain duties necessary for life, but the protoplasm was the true living substance and retained all the properties of life.The metaplasm which later became known as the ergastic substances, included the cell sap, starch grains, crystals and the extracellular matrix.Under the brightfield microscope, the cytoplasm appears as a fine dispersion of particles of different sizes (1-10 m), freely suspended in a liquid medium. This led Hanstein to propose that the granules form the fundamental nature of cytoplasm (Figure 9-1), that is of life. Hanstein (1882) named the granules, "microsomes"-- a term later used by Albert Claude to designate a membrane fraction isolated from rat liver cells