The application of phase-contrast to the ultra-violet microscope

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Abstract
It has been shown that the phase-contrast principle of Zernike may be applied with advantage to ultra-violet microscopy and that certain advantages follow: ( a ) In the first place, it furnishes a more certain method than dark-ground illumination for the visual selection of a suitable field of view as all structures are more clearly revealed. ( b ) In the second place, it furnishes a new means whereby structural details that give rise to a change of phase in the transmitted radiations may be photographed in contrast, even under conditions when selective absorption does not take place. ( c ) In the third place, it is possible, after having selected a suitable field by means of visual phase-contrast, to photograph the same field in ultra-violet light and then to turn once again to the visual phase-contrast image to make certain that the exposure has not caused damage to a living organism. A series of explanatory photographs has been taken covering a wide range of biological objects. These show that the method is sensitive to minute changes in phase and that the resulting images are characterized by good contrast. Details are revealed that cannot be brought out by normal methods, as will be clear from a close study of the pairs of photographs which accompany this paper. In selecting these it was thought necessary to avoid very fine detail and delicate shades of contrast that would be lost in the process of reproduction.
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