The outer membrane of Escherichia coli, which is composed of proteins, phospholipids and lipopolysaccharides, is assumed to have passive diffusion pores for small hydrophilic molecules. We discussed on the properties of these hypothetical pores on the basis of the results previously reported. We also described about a structural lipoprotein of the E. Coli outer membrane, which is a possible candidate for the passive diffusion pores.

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Using a semi-floating glass microelectrode, the permeability of the peritubular membrane for Na, K. HCO₃ and Cl was studied in the rat kidney proximal tubule in vivo. The magnitude of the change in membrane and transepithelial p.d. due to peritubular ionic replacement was analyzed by means of an equivalent circuit analysis. The results of the present study showed that the peritubular p.d. is composed mostly of the diffusion p.d. of K and HCO₃. The contribution of Na and Cl to the membrane current appears to be negligible. The transference number of the peritubular cell membrane was 0.57 for K, 0.42 for HCO₃ and less than 0.01 for Na.

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The mechanism of action of calcium ion on the troponin-tropomyosin-actin system was briefly reviewed. Direct action of calcium on myosin was discussed, and throught to be not important in physiological control of contraction and relaxation. Mechanical properties, such as maximum shortening velocity, length-tension relation, rate of tension development etc., of skinned muscle fibers partially activated by calcium were described, which are still to be explained on a molecular basis.
The mechanism of uptake of calcium by the sarcoplasmic reticulum (SR) was briefly reviewed. Calcium releasing action of calcium ion itself and that of "depolarization" of the SR were described. Calcium ion itself was shown to be not playing an essential role in phyiological excitation-contraction coupling of skeletal muscle. Recent progress in excitation-contraction coupling other than that with skinned fibers was briefly reviewed.

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Recent trends of the study of molecular evolution are briefly reviewed in relation with the theory of population genetics. Similar aspects of the population genetics theory and statistical mechanics are pointed out, and it is suggested that the both could adequately viewed as branches of population science. In order to grasp them in a unified way, an attempt is made of an axiomatic formulation of population science, by which some characteristics of models of statistical mechanics, population ecology, and population genetics are described.

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