THE process consists primarily of filming rapidly JL moving micro-organisms by means of intermittent light. The source of light is an open arc-light and the intermittent character is obtained by rotating, at high speed, a suitable disc, pierced by one or several slots, between the arc and the microscope. The number of exposures per second obtained in this way is almost unlimited while the time of each exposure can be made very small. Thus if the disc is rotating at 100 rev. a second, and there are 12 slots in it, the number of exposures will be 1,200 a second. If each slot subtends an angle of 1°, the exposure will be 1/100 x 1/360 = 1/36,000 sec.
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