. A civic biology : presented in problems. Biology; Sanitation. PLANTS WITHOUT CHLOROPHYLL 141 (d) exposed at the level of a dirty and much-used city street. (e) exposed at the level of a well-swept and little-used city street. (/) exposed in M city park. (g) exposed in a factory building. (h) dirt from hands placed in dish. (•/) rub interior of mouth with finger and touch surface of dish. (;/) touch surface of dish with decayed vegetable or meat. (A1) touch surface of dish with dirty coin or bill. •(/) place in dish two or three hairs from boy's head. This list might be prolonged indefinitely
. A civic biology : presented in problems. Biology; Sanitation. PLANTS WITHOUT CHLOROPHYLL 141 (d) exposed at the level of a dirty and much-used city street. (e) exposed at the level of a well-swept and little-used city street. (/) exposed in M city park. (g) exposed in a factory building. (h) dirt from hands placed in dish. (•/) rub interior of mouth with finger and touch surface of dish. (;/) touch surface of dish with decayed vegetable or meat. (A1) touch surface of dish with dirty coin or bill. •(/) place in dish two or three hairs from boy's head. This list might be prolonged indefinitely. Now let us place all of the dishes together in a moderately warm place (a closet in the schoolroom will do) and watch for results. After a day or two little spots, brown, yellow, white, or red, will begin to appear. These spots, which grow larger day by day, are colonic* made up of millions of bacteria. But probably each colony arose from a single bacterium which got into the dish when it was exposed to the air. How we may isolate Bacteria of Certain Kinds from Others. - In order to get a number of bacteria of a given kind to study, it becomes necessary to grow them in what is known as a pure culture. This is done by first growing the k'H-teria in some medium such MS beef broth, gelatin, or on Then as growth follows the colonies of bacteria appear in the culture media or the beef broth becomes cloudy. If now we wish to study one given form, it becomes recessary to isolate them from the others. This is done by the following process: a platinum needle is first passed through a flair e to sterilize it; that is, to kill all living things that may be on tie needle point. 1 For directions for making a culture medium, see Hunter, Laboratory Problems in Civic Biology. Culture tubes may be obtained, already prepared, from Parke, Davis, and Company or other good ( 'olonirs of l).-iclcri;i m-owing in a petri Please note that these images are extracted from
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