JAMA. 1903;XLI(2):104-105. doi:10.1001/jama.1903.04470040032013.
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During the last few years bacteriologists have come to attribute a rapidly increasing number of diseases to microbes that are too small to be seen with our best microscopes.1 With these instruments and the ordinary method of illumination Helmholtz and physicists in general tell us that it is not possible to get a clear image of an object that is less than ¼ micron in diameter. Recently, however, two German physicists, Siedentopf and Zsigmondy2 have perfected an apparatus by means of which they are enabled to see particles having a diameter of 0.005 micron or even less. They make use of the best microscope that can be furnished by Zeiss and illuminate the preparation to be examined with a cone of intense sunlight or light from an electric arc. The light is concentrated by means of a system of condensors, and the vertex of the cone thus formed


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