. Biophysical science. Biophysics. Figure 2. Bacterial plates for three different dilutions. The left hand plate represents a 107:1 dilution which shows too few clones for meaningful counting, whereas the right hand one, a 105:1 dilution, has far too many. However, the middle one, diluted 106:1, shows about 50 clones. By counting duplicate plates at this dilution, one can find the original con- centration of bacteria at the time of plating. It is unlikely that the initial bacterial concentration will be in a range suitable for plating. Accordingly, a series of dilutions are made, each differin
. Biophysical science. Biophysics. Figure 2. Bacterial plates for three different dilutions. The left hand plate represents a 107:1 dilution which shows too few clones for meaningful counting, whereas the right hand one, a 105:1 dilution, has far too many. However, the middle one, diluted 106:1, shows about 50 clones. By counting duplicate plates at this dilution, one can find the original con- centration of bacteria at the time of plating. It is unlikely that the initial bacterial concentration will be in a range suitable for plating. Accordingly, a series of dilutions are made, each differing by a factor of 10. A few members of such a series are shown in Figure 2. On plates where the dilution is too great, too few clones develop to make counting statistically meaningful. On plates made up with too high a concentration of bacteria, many spots originate from two or more of the bacteria placed on the plate, and many clones overlap. In the extreme case, the entire plate will be covered with bacteria. Figure 2 illustrates typical plates after they have been incubated for two days. When phages are studied by a plating method, bacteria are used at a concentration which would completely cover the plate in the absence of phage particles. If phages are present, clear areas develop on the sur- face of the plate. These result because each phage particle multiplies inside a bacterium until the cell wall is eventually ruptured. For every bacterium infected, as many as 300 new phage particles are sometimes produced. The new phage particles then enter other bacteria surrounding. 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 Ackerman, Eugene, 1920-. Englewood Cliffs, N. J. , Prentice-Hall
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