. Adventures with animals and plants. Biology. he wishes to study. When the needle is then touched to a fresh agar slant, a new colony of the same kind will form be- cause some bacteria have been "trans- ; In this way it is easy to start pure cultures, that is, cultures containing only one kind of bacterium. Identifying bacteria. Some bacteria can be identified merely from the appearance of the colony. Some colonies are smooth, others are rough; some are white, others have a distinct color such as yellow or red. Generally one cannot determine the exact kind of bacteria by the
. Adventures with animals and plants. Biology. he wishes to study. When the needle is then touched to a fresh agar slant, a new colony of the same kind will form be- cause some bacteria have been "trans- ; In this way it is easy to start pure cultures, that is, cultures containing only one kind of bacterium. Identifying bacteria. Some bacteria can be identified merely from the appearance of the colony. Some colonies are smooth, others are rough; some are white, others have a distinct color such as yellow or red. Generally one cannot determine the exact kind of bacteria by the appearance of the colony. Examining bacteria through a microscope helps somewhat in identifying them. But even after mi- croscopes had been improv^ed to mag- nify looo times or more, it was still diffi- cult to see bacteria because they were so transparent and so tiny. Koch and other bacteriologists discovered chemicals that dyed or stained the bacteria but did not stain other cells. This was of great value because staining made it possible to see and identify bacteria in body tissues. If you have a school laboratory, it will be possible to prepare a pure culture and to stain bacteria, as described in Exercises 4 and 5. If you have dishes of nutrient agar, you can easily test for the presence of bacteria in air, in water, and on objects outside the body. See Exer- cises 6 and 7. Favorable and unfavorable conditions for growth. Bacteria will grow and repro- duce onlv if kept moist and at a proper temperature. Like other organisms that lack chlorophyll, they depend on manu- factured food. By doing Exkkcisk 8 you can determine for yourself to what ex- tent external conditions afl'ect the Constant Care Is Needed for Health unit v\. Fig. 290 How iiia7iy colonies of bacteria can you find oti this agar plate? How many bacteria were introduced? (Brooklyn botanic garden) growth of bacteria. In general, bacteria are not killed by low temperatures but they fail to reproduce unless the te
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