Physiological systems can be identified systematically and efficiently by use of the nonlinear or white-noise analysis technique whose theoretical ground was laid by Wiener in 1942. The technique uses statistical, unbiased random noise as input to probe a system and identifies it through the process of cross-correlation, whereas the traditional approach uses purpose-oriented inputs to prove or disprove a particular and often limited aspect of a system's function.
Since our first application of the technique to define transfer functionals of neuron chains in catfish retina, many advances have been made in the theoretical as well as practical aspects of the theory. An introductory book on the subject was written by the Marmarelis brothers (Marmerelis and Marmarelis, 1977) and the latest theoretical advance is seen in Yasui's paper (Yasui, 1979). White-noise signals to probe biological systems now encompass such inputs as spatio-temporal random light signals, current injected into a point in a complex nervous system, and binary or ternary signals.
In our study of catfish retina, (first order) Wiener kemels were related to such traditional but moot concepts as the Weber-Fechner relationship or the Michaelis-Menten equation. Temporal as well as spatial dynamics of neurons in catfish retina have been defined by use of multi-input random signals or the one-dimensional random travelling grating devised by Yasui.
Although the technique may not be immediately accepted by biologists, it will, in the long run prove to be a valuable tool for studying complex biological systems.

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Recently, the mesomorphic structure has been found in the molten and dissolved states and even the solid state of many kinds of polymers. The history of polymer liquid crystals is surveyed briefly in this paper. Polymers which exhibit a liquid crystalline phase are classified into semiflexible or rigid polymers, according to the flexibility of their main chain, or into polymers with mesogenic side groups, polymers with rigid segments, or polymers with a rigid block, depending on their molecular structure. The liquid crystalline structure of these polymers is interpreted on the basis of the molecular structure. Recent theoretical works on the formation of lyotropic polymer liquid crystals and on the structure and properties of polymer liquid crystals are also briefly reviewed. The application of polymer liquid crystals is discussed, taking account of the characteristics of polymer liquid crystals.

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Many biologically active substances exert their activity as the result of a specific interaction with a cellular component, the receptor, that triggers off the sequence of biological events leading to the final response. Thus the mode of interaction of a bioactive compound with the receptor would be best understood by analysing its interaction with the isoloated receptor molecule.
In case of plant hormones, binding protein(s) can be isolated but can not at present be identified as the real receptor. Indirectly, however, the quantitative structureactivity relationship can be used to probe the binding between a bio-active molecule and its receptor. This methodology assumes that the variation in biological activity of a series of compounds reflects differences in both the permeability of the environment to these compounds and their affinity to the active site. Thus the results of the analysis are thought to reflect the interaction profile in terms of physical and structural parameters if the permability factor is of little significance or considered separately. In this sense, the methodology has been applied to the analysis of cytokinins, a class of plant hormomes which consists of two series of compounds, N⁶-substituted adenines arid diphenylureas. The results for adenylate cytokinins indicated an optimum steric condition for activity in terms of the maximum width of the N⁶-substituent. The electron-withdrawing effect is thought to enhance the activity through both series. Position-specific steric and hydrophobic effects of substituents on the benzene ring of the diphenylureas were suggested to participate in the variation of activity. Based on inferences made from the analyses, a hypothetical map for the mode of interaction of these two sets of cytokinins at the site of action has been proposed.

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Antisera to bovine serum albumin were raised in rabbits. Studies of immunological activities of some of the fragments from bovine serum albumin and other species of serum albumins showed that immune response is dynamic rather than static. The results of immunological activities of fragments of bovine serum albumin were analyzed carefully and 5 regions of the molecule were predicted to be antigenic determinants. Synthesis of these regions confirmed this prediction. These results suggest that the serum albumin molecule has at least a partially repeated antigenic structure.

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The recent development of magnets to produce a stable static field and of computers to process the data and to control the apparatus has improved the resolution of NMR spectra and the detection of NMR relaxation times. NMR is now being used as a non-destructive method for measuring substances in living tissues. This paper reports the application of NMR to living tissues, nervous tissue and muscle, together with methods of maintaining these tissues under physiological conditions during NMR measurement.
The methods of maintaining tissue in the living state are: (1) perfusion of a solution into the NMR tube, (2) freezing of tissue with liquid nitrogen, and (3) insertion of living material and supplying air into the NMR tube. ³¹P-NMR spectra of crayfish ventral nerve cords and brain slices of guinea pig under perfusion with spinning showed the resonances of Pi, sugar phosphates and high-energy phosphorus compounds. Both frozen rat brain and the head of mouse in vivo showed almost the same ³¹P-NMR spectra, and the time courses of signal intensities of the phosphorus compounds in the former were obtained. ¹H- and ³¹P-NMR were applied to frog muscle. Measurements of ¹H-NMR transverse relaxation time showed that water in the muscle is composed of three fractions. ³¹P-NMR spectra of frog muscle at rest and after tetanus stimulation showed metabolic changes in phosphocreatine, Pi, and sugar phosphates, and changes of intracellular pH. The decrease of Pi and the increase of phosphocreatine after tetanus stimulation showed the same time course.

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