| We are trying to find a way to measure the characteristics of the biological systems, and we find two ways to detect it as the following.When a suspension consisting of electric particles having nonlinear characteristics is subjected to a sinusoidal alternating current (ac) electric field, the electric response will generally consist of ac fields at frequencies of higher-order harmonics. We experimentally report on harmonic generation by erythrocytes subjected to an ac electric field. We find that both even and odd harmonics are sensitive to cell shapes, conductivities, field frequencies, and field magnitude. Theoretical analysis based on a phenomenological model yield predictions that are in excellent agreement with the experiments. Thus, it becomes possible to detect nonlinear characteristics, shapes, and conductivities of erythrocytes by measuring such ac responses.On the other hand to develop an accurate and convenient method for measuring the heart rate of zebra fish in vivo, a system combining fast differential interference contrast (DIC) imaging with an autocorrelation technique is established. The imaging correlation coefficient corr(i, j) between frame i, selected from the obtained time-lapse imaging series as the reference image, and any other frame j, is calculated as the time-dependent cycle course. Heat rate is determined by the cycle period of the corr with a high temporal resolution of 4 ms, achieved by fast charge-coupled device (CCD) imaging of 250 frames per second. With this high-resolution system, we find that 1mg/L cadmium not only induces the slowing of the heart rate, but also caused signs of arrhythmia in treated fish.
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