. A text-book of bacteriology, including the etiology and prevention of infective diseases and a short account of yeasts, and moulds, haematazoa, and psorosperms. Bacteriology. 80 BACTERIOLOGY. the medium in which the section is mounted, nothing would be visible under the microscope. As, however, the cells and their nuclei, and the tissue fibres do differ in this respect, the rays which pass through them are diffracted, and an image of lines and shadows is developed. If in such a tissue there were minute coloured objects, and if it were possible to mount the tissue in a medium of exactly the s
. A text-book of bacteriology, including the etiology and prevention of infective diseases and a short account of yeasts, and moulds, haematazoa, and psorosperms. Bacteriology. 80 BACTERIOLOGY. the medium in which the section is mounted, nothing would be visible under the microscope. As, however, the cells and their nuclei, and the tissue fibres do differ in this respect, the rays which pass through them are diffracted, and an image of lines and shadows is developed. If in such a tissue there were minute coloured objects, and if it were possible to mount the tissue in a medium of exactly the same refractive power, the tissue being then invisible, the detection of the coloured objects would be much more easy. This is exactly what is required in dealing with bacteria which have been stained with aniline dyes, and the desired result can be obtained by the use of the sub-stage condenser. If we use the full aperture of the condenser the greatly converged rays play on the component parts of the tissue, light enters from. Fig. 24.—Ramsden Micbometee Eye-piece. all sides, the shadows disappear, and the structure picture is lost. If now a diaphragm is inserted, so that we are practically only dealing with parallel rays, the structure picture reappears. As the diaphragm is gradually increased in size the structure picture gradually becomes less and less distinct, while the colour jjicture, the image of the stained bacteria, becomes more and more intense. When, therefore, bacteria in the living condition and unstained tissues are examined a diaphragm must be vised, and when attention is to be concentrated upon the stained bacteria in a section or in a cover-glass preparation, the diaphragm must be removed and the field flooded ^vith light. Micrometer.—For the measurement of bacteria a stage micro- meter may be used with a camera lucida". The stage micrometer consLsts of a slip of thin glass ruled with a scale consisting of tenths and hundredths of a millimetre. The im
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Keywords: ., bookcentury1800, bookdecade1890, bookpublisherphila, bookyear1897
