THE FINE STRUCTURE OF BIOLOGICAL SYSTEMS

Abstract

Summary 1. Present‐day interest in the study of fine structure may be traced back to the work of the botanist, Carl Nägeli, to whom the conception of the micell is due. 2. The continuation of Nageli's optical studies of biological structures, the development of X‐ray analysis, and the investigation of the properties of long chain high polymers, have led to the extension and modification of Nägeli's ideas. 3. Two main types of molecular aggregate are of particular importance in biological systems—linear (or fibrous) and laminar structures. These may be classified as subcellular, extracellular and supracellular. 4. The subcellular structures which have been examined include: protein fibres from the sap of virus‐infected plants; chromosomes; asters and spindles; and contractile fibrils (muscle fibrils, myonemes, pseudopodia and cilia). These all appear to be composed of chain molecules arranged approximately parallel to the long axis of the structure in question. Laminar subcellular structures include the surface membranes of animal cells (nerve fibres, echinoderm eggs, red blood corpuscles) and the outer portion of the rods and cones of vertebrate retinae. These are composed apparently of alternating layers of protein and lipoid molecules. 5. Extracellular fibrous structures are represented by elastoidin, collagen, elastin and chitin; laminar structures by the keratinous egg cases of selachians, the cellulose test of tunicates and chitinous integuments in general. The relation of these to other natural and synthetic high polymers is discussed. 6. The category of supracellular Structures, that is, of macroscopic fibrous or laminar structures of multicellular origin includes (a) hair and muscles, and (b) enamel and bone. 7. It is clear that a close parallel in structure and behaviour exists between biological materials and high polymer substances. The morphological implications of this parallel are discussed and the importance of molecular morphology for the biologist is considered.