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The French pressure cell or “French press”, invented by Stacy French of the Carnegie Institution of Washington, D. C., is used to disrupt cells by passing them through a narrow valve under high pressure. It can disrupt plant and microbial cell walls while leaving the nuclei intact. Other uses include disintegrating chloroplasts, animal tissue homogenates and other biological particles. A French press is commonly used to break the resilient cell walls of bacteria and other microorganisms for isolation of proteins, enzymes and other cellular components. The press uses a hydraulic pump to drive a piston within a larger cylinder that contains the liquid sample. The highly pressurized sample is then squeezed through a needle valve during which the fluid undergoes shear stress and decompression, causing cellular disruption. The major components of the press are made of stainless steel to prevent sample contamination. In the press, shear forces are carefully controlled by adjusting the piston pressure. The press provides a single-pass through the point of maximum shear force, limiting damage to delicate biological structures due to repeated shear, as can occur with other disruption methods. Before use, the pressure cell is chilled to preserve enzymatic and other biological activities of the sample. Disadvantages of the press include its inapplicability for large sample volumes, and its difficulty to move, manipulate and clean due to its heavy weight (~15 Kg). Additionally, certain types of samples may clog the valve.