Abstract: A bioreactor for cell culture medium is provided including a flask for holding the culture medium, a screen at or just below the surface of the culture medium, a mover for the screen to cause it to move generally parallel to the surface of the culture medium, and an integral or separate impeller to cause circulation of the culture medium to the surface of the liquid culture medium. The screen is preferably on a float, and is connected to be driven at different levels of the liquid in the flask.

Abstract: An oscillatory mechanism, designed particularly for use in a laboratory shaker, includes a member, or a system of members, arranged to perform oscillatory movements, the transmission of power to that member or system, whereby its oscillation is caused or maintained, being by means of fluid pressure, the mechanism comprising means defining one or more chambers each having an inlet connectible to a source of pressurized fluid and an outlet through which, when open, pressurized fluid supplied to each chamber can escape; the respective chamber being expansible under the action of said pressurized fluid when each said outlet is closed; and wherein the motion of the oscillatory member or system in operation cyclically opens and closes each said chamber outlet, the consequent expansion of the respective chamber upon closure of the outlet delivering an impulse to said member or system whereby the oscillation thereof is caused or maintained.