. Laboratory work in bacteriology. Bacteriology. 434 BACTEBIOLOGY. Inasmuch as the bacteria are liable to multiply rapidly, especial- ly if the water is taken from a cool source and is then kept at ordinary temperature, it is advisable to plate the water at the time it is collected. Under these circumstances, instead of plates or Petri dishes, flat flasks or bottles can be used. These contain the requisite amount of sterile gelatin which is inoculated with the water as soon as it is drawn. The flask is placed on its side, and, when the gelatin solidifies, it can be taken back to the laboratory
. Laboratory work in bacteriology. Bacteriology. 434 BACTEBIOLOGY. Inasmuch as the bacteria are liable to multiply rapidly, especial- ly if the water is taken from a cool source and is then kept at ordinary temperature, it is advisable to plate the water at the time it is collected. Under these circumstances, instead of plates or Petri dishes, flat flasks or bottles can be used. These contain the requisite amount of sterile gelatin which is inoculated with the water as soon as it is drawn. The flask is placed on its side, and, when the gelatin solidifies, it can be taken back to the laboratory. If only a small number of colonies are present they can be counted with the unaided eye, but when, as it fre- quently happens, the number is very large, it is desirable to make use of a counting apparatus. Fig. 57 shows the counting apparatus of WolfEhiigel, which is usually em- ployed when ordinary glass plates are used. The gelatin plate, on which the colonies are to be counted, is placed on the black glass base and covered with a glass plate ruled into squares. The number of colonies under each square can thus be easily determined. When possible, the number of colonies under each square should actually be counted. As a rule, however, it is customary to count the number of colonies found under each of 6, 8 or 10 squares selected at random from over the surface of the plate. The average number present in one square is then Fig. 57. Wolffhugel's apparatus for counting colonies. The total number of colonies on the plate is found by determining the number of square centimeters which the gel- atin on the plate covers, and multiplying this figure by the average number of colonies per square. Since each colony. 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 Novy, Frederick George, 1864- . Ann Arb
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