This paper describes how microcinematographic pictures were made of the agglutination process of typhoid bacilli (both H and 0), and what the resulting 16 mm. films showed. TECHNIQUE The technique used was described in detail in a previous paper on the microcinematography. of the motile organs of typhoid bacilli (1940). Here the following chief points may suffice. Sunlight was taken as the source of light. It was brought direct from a heliostat mirror through a 2-meter focus collector lens to

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... e dark ground condenser of the microscope. No further mirrors, nor coolers, nor light filters were employed. This had been proved to be the only way to get sufficient light onto the photographic film. The darkground condenser was the Siedentopf cardioid. Of great help were the combined glass-mica microscope slides, invented by Zeiss, which provide a perfectly clean surface by splitting off a layer of mica. With glass slides it is very difficult to get a perfectly dark background.' The objective used was the Zeiss oil-immersion apochromat, 35 X, N. A. 0.85. In combination with the Zeiss photographic eye-piece 4 X, and a distance of 15 cm. between microscope and cinema film, a magnification of a little over 50 was reached. This proved ample for all details, and low enough to send sufficient light to the photographic film.