. Bacteriological methods in food and drugs laboratories : with an introduction to micro-analytical methods . Bacteriology; Food; Drugs. 98 BACTERIOLOGICAL METHODS absorbed portion is supposedly hydrogen. The colon bacillus shows a gas formation of 3-^ hydrogen. The standard time of incubation is 48 hr., but if colon bacilli are abundant, gas forma- tion will be observed in the tubes carrying the larger amounts of the inoculated material at a much shorter time, occasionally within a few hours. Small numbers of attenuated colon bacilli may require 2 and 3 days before there is any gas formation
. Bacteriological methods in food and drugs laboratories : with an introduction to micro-analytical methods . Bacteriology; Food; Drugs. 98 BACTERIOLOGICAL METHODS absorbed portion is supposedly hydrogen. The colon bacillus shows a gas formation of 3-^ hydrogen. The standard time of incubation is 48 hr., but if colon bacilli are abundant, gas forma- tion will be observed in the tubes carrying the larger amounts of the inoculated material at a much shorter time, occasionally within a few hours. Small numbers of attenuated colon bacilli may require 2 and 3 days before there is any gas formation noticeable. In this connection it may be mentioned that the attenuated colon bacilli indicate remote contamination, as all B. coli of recent contamination develop readily in lactose Fig. 26.—Bacillus coli. Superficial colony on a gelatin plate —{McFarland after Heim.) days old (X 21). This constitutes the usual presumptive test for the presence of sewage contamination. Some investigators, however, recommend that the test be supplemented as follows: Plant the suitable quantities or dilutions into liver broth (in test-tubes) and in- cubate at 37° C. for about 12 hr. and then transplant these cultures into the lactose bile as above explained. The liver broth en- richment medium is said to bring out the attenuated forms of colon bacilli. In routine procedures the liver broth culturing is usually omitted as the important point at issue is the determina- tion of fairly recent contamination with sewage, or of sewage. 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 Schneider, Albert, 1863-1928. Philadelphia : P. Blakiston's Son & Co.
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