. The principles of bacteriology; a practical manual for students and physicians. Bacteriology. BACTERIUM DIPHTHERIA 461 be recognized. They are in every way more delicate in structure than when on the serum mixture. They appear at first, when on the surface, as very flat, almost transparent, dry, non-glistening, round points which are not elevated above the surface upon which they are growing. When slightly magnified they are seen to be granular, and to present an irregular central marking, which is denser and darker by transmitted light than the thin, delicate zone which surrounds it. As the
. The principles of bacteriology; a practical manual for students and physicians. Bacteriology. BACTERIUM DIPHTHERIA 461 be recognized. They are in every way more delicate in structure than when on the serum mixture. They appear at first, when on the surface, as very flat, almost transparent, dry, non-glistening, round points which are not elevated above the surface upon which they are growing. When slightly magnified they are seen to be granular, and to present an irregular central marking, which is denser and darker by transmitted light than the thin, delicate zone which surrounds it. As the colony increases in size the thin granular peripheral zone becomes broader, is usually marked Fig. 82 m--^ @ ft Colonies of bacterium diphtherise on glycerin-agar-agar. a, colonies located in the depths of the medium; b, colonies just breaking out upon the surface of the medium; t, fully developed surface-colony. by ridges or cracks, and its periphery is notched or scalloped. (Fig. 80, c.) These colonies are always quite dry in ap- pearance. When deep down in the agar-agar they are coarsely granular. (Fig. 80, a.) They rarely exceed 3 mm. in diameter. Gelatin.—On gelatin the colonies develop much more slowly than on media that can be retained at a higher tem- perature. They rarely present their characteristic appear- ances on gelatin in less than seventy-two hours. They then appear as flat, dry, translucent points, usually round in Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Abbott, Alexander Crever, 1860-1935. Philadelphia, Lea & Febiger
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