High-Speed Cinematography of Microscopic Organisms

Abstract

Many cells bear thin, hair-like appendages about 0.2 µm in diameter and between 10 and 500 µm long, called cilia or flagella. For flagella which beat rhythmically in a plane and can be constrained to move within the field of an optical microscope, stroboscopic techniques can be used to observe and analyse the motion. Flagella of many cells execute a threedimensional beat, while other important movements occur spasmodically. Such non-repetitive behaviour is not amenable to stroboscopic observation but requires a technique in which individual images are recorded as a function of time. One such technique is high-speed cinephotography, which has been used to obtain information about the movement of a variety of cells.

To illustrate the effectiveness of the method, we describe a series of experiments in which active flagella were damaged by firing a laser through the microscope from eyepiece to objective in such a way that the laser beam was focused on a local region of the flagellum. High-speed cinephotography was used to record the response of the system to laser damage, and the results are of importance to our understanding of the molecular machinery within the flagellum which is responsible for the externally observed motility.

The use of high-speed cinephotography generates much material for subsequent analysis. To facilitate interpretation of our photographs we have modified a standard back-projection system to provide a semi-automatic, computer-controlled instrument which will track along the image of a flagellum and record the coordinates of the centre-line. If required, preliminary processing of the results can be effected in the computer, which will then present the data in a form suitable for further analysis.