A previous note (Barnes, '36) reported that concentrated heavy water reduces the potential of frog skin. The present paper presents additional evidence together with a comparison of the effects of heavy water and temperature. The susceptibility of frog skin potential to temperature was early recognized, notably by Hermann, Engelmann, von Gendre and Biedermann (compare Lesser, '07)' but their results were obscured by the lack of oxygen supply and balanced salt solution. The interpretation of temperature effects on bioelectrical potential has played an active part in both the 'metabolism' school of Hermann (and more recently of Lund) and the 'ionic' school of Bernstein and later workers. Lund and Moorman ('31) described the effect of temperature changes on frog skin over the range 26.4 to 16.4"C. but not below. The Q1, values of Francis ('33) for Rana temporaria are based on only three skins. Klopp's ( '24) study was confined to the injurious effects of high temperature.

A laser tweezer (LT) along with advanced imaging techniques has been widely applied to manipulate and study living as well as nonliving microscopic objects. In this study we present yet another novel application of LTs for a precise measurement of the viscosities of fluids in a micro-volume flow. We have demonstrated this novel application by measuring the viscosity of a fetal bovine serum (FBS) using a LT constructed from a single intensity gradient laser trap. By calibrating the LT using dielectric silica micro-beads in a fluid with a known viscosity, specifically water, and by suspending same size of silica beads in the FBS and trapping with the same trap, we have determined the viscosity of the FBS at different temperatures. We have used the relationship between the trapping and Stoke's drag force for a constant drag speed to determine the viscosity. We have also analyzed the viscosities determined in comparison with corresponding viscosities measured using an Ostwald viscometer.

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In the study of the mechanical properties of the erythrocytes (red blood cells-RBCs) the blood sample is commonly diluted in fluids that do not compromise the integrity of the cells. Fetal bovine serum (FBS), newborn bovine serum (NBBS), and phosphate buffer (PBS) solution with a concentration that can provide the right osmotic pressure are fluids commonly used to dilute the blood samples in such studies. Here we have presented the effect of these fluids on the elastic properties of the RBCs that we studied using laser traps. Two laser traps are directly used to trap and deform the cell by exerting a force distributed on the entire cell. The relative changes in size of the cell are studied as a function of the applied force to investigate any effects on the mechanical deformability of RBCs when the cells are suspended in these fluids. The results have shown that the elasticity of the RBCs in the NBBS is not statistically different from the elasticity of the cells in the PBS solution; however the results for the elasticity of the cells in FBS are found to be significantly higher.

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