Essentials of bacteriology; being a concise and systematic introduction to the study of bacteria and allied microörganisms . c.). This first tube is called original. From this three drops(taken with the looped platinum rod, Fig. 11, p. 45) areplaced in a second tube, the rod being shaken somewhat in the 8o ESSENTIALS OF BACTERIOLOGY gelatin or agar; this is labeled first dilution (a colored pencilis useful for such markings). From the first dilution threedrops are taken into a third tube, which becomes the seconddilution. The plugs of cotton must be replaced after each inocula-tion, and while
Essentials of bacteriology; being a concise and systematic introduction to the study of bacteria and allied microörganisms . c.). This first tube is called original. From this three drops(taken with the looped platinum rod, Fig. 11, p. 45) areplaced in a second tube, the rod being shaken somewhat in the 8o ESSENTIALS OF BACTERIOLOGY gelatin or agar; this is labeled first dilution (a colored pencilis useful for such markings). From the first dilution threedrops are taken into a third tube, which becomes the seconddilution. The plugs of cotton must be replaced after each inocula-tion, and while being held must be carefully protected fromcontamination. Glass Plating.—The larger the surface over which thenutrient medium is spread, the more isolated will the coloniesbe; window glass cut in rectangular plates 6x4 inches insize was formerly used, but now Petri dishes consisting of2 circular glass or porcelain dishes, one fitting over the otheras a cover, are universally employed (Fig. 24). They aresterilized, the softened and inoculated agar or gelatin ispoured from the test-tube into the dish with as much speed. Fig. 24.—Petri dish for making plate cultures. as possible, and the lid replaced, avoiding contaminationfrom the air and surroundings. They are labeled or markedwith pencil, and placed in the incubator or kept at roomtemperature for further development. This method is very useful for transportation, and doesaway with the cooling apparatus and moist chamber for-merly employed; the saucers can be viewed imder micro-scope similar to the glass plates, and have entirely super-seded them. Esmarchs Tubes or Rolled Cultures.—This method,especially used in the culture of anaerobic germs, consists inspreading the inoculated gelatin upon the inner walls of thetest-tube in which it is contained and allowing it to congeal. INOCULATION OF CULTURE-MEDIA 8l /?~\ The colonies then develop upon the sides of the tube withoutthe aid of other apparatus. The method is useful wh
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