. Pathogenic microörganisms; a practical manual for students, physicians, and health officers . perhour. Movement is influenced by many factors, such as chemicals (theoxygen in the air especially), heat, light, and electricity. The tactileproperty which enables microorganisms to take cognizance of variousforces is known as taxis; when forces attract, the phenomenon is knownas positive taxis and when they repel, it is called negative taxis. Chemo-taxis, or the effect of chemicals, is taken up in detail on page 59. Growth and Reproduction.—Under favorable conditions bacteriagrow rapidly to a ce
. Pathogenic microörganisms; a practical manual for students, physicians, and health officers . perhour. Movement is influenced by many factors, such as chemicals (theoxygen in the air especially), heat, light, and electricity. The tactileproperty which enables microorganisms to take cognizance of variousforces is known as taxis; when forces attract, the phenomenon is knownas positive taxis and when they repel, it is called negative taxis. Chemo-taxis, or the effect of chemicals, is taken up in detail on page 59. Growth and Reproduction.—Under favorable conditions bacteriagrow rapidly to a certain size, more or less constant for each species,and then divide by fission into approximately equal halves. Theaverage time required for this cycle is twenty to thirty in all species the nuclear material divides first. This iscertainly the case in the group to which the B. diphtherioe belongs,where division of the nuclear granules may be observed in the livingorganism before the characteristic snapping of the cell body and wheredivision into equal halves seldom Fio. 4.—Successive stages in division of B. diphtherise, showing relation of line of divisionto metachromatic granule. Continuous observation of living bacillus drawn withoutcamera lucida. (Williams.) According to our observations on the living cell of members of this group,division takes place at a point occupied by a metachromatic granule (Fig. 4).Before division of the cell body the metachromatic granule, which appearsto contain nuclear substance, elongates and shows a darker line at or nearits centre. This seems to divide and form two lines, each of which has at apoint near the surface a very tiny, refractive granule, staining deeply withchromatin stains. Between these two lines the cell body suddenly divideswith a snap, like the opening of a jack-knife, division beginning at the pointbetween the two tiny granules, and the two new cells remain for a variabletime attached at opposite
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