| Summary: | This paper describes the development of a miniature, temperature-controlled, stainless steel pressure chamber which uses strain-free optical glass for windows. It is directly adaptable to standard phase-contrast and polarized-light microscopes and requires a minimum amount of equipment to generate and measure pressure. Birefringence retardations (BR) of 0.1 nm up to 3,000 psi, 0.4 nm up to 5,000 psi and 1.0 nm up to 10,000 psi can be detected over a 0.75-mm central field with two strain-free Leitz 20 • UM objectives, one used as a condenser. In phase-contrast studies a Nikon DML 40 • phase objective and Zeiss model IS long working-distance phase condenser were used, with little deterioration of image quality or contrast at pressures as high as 12,000 psi. The actual design process required a synthesis of various criteria which may be categorized under four main areas of consideration: (a) specimen physiology; (b) constraints imposed by available optical equipment and standard microscope systems; (c) mechanical strength and methods for generating pressure; and (d) optical requirements of the chamber windows. Procedures for using the chamber, as well as methods for shifting and controlling the temperature within the chamber, are included. Hydrostatic pressure is important as a physiological parameter in relation to life in the deep sea and as an experimental variable, especially in studies of the equilibria of labile cellular structures and the reaction rates of enzymatic processes. (For details
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