Most living beings do not support cold or excessive heat. When the temperature is very high, the chemicals essential to life are destroyed, and when it is very low, the chemical reactions needed to supply the energy needed for growth occur at a rate too slow to make life possible. However, there are microorganisms capable of living and growing at the freezing temperature of water.
Some spectacular examples of this type are not offered by algae, which grow so profusely on the surface of the snowy fields of the Arctic that they colour the snow red and green. Freezing, on the other hand, does not always destroy bacteria; this was demonstrated recently when, after thawing some samples of human excrement found in the huts of an explorer in 1913, living intestinal bacterial cells appeared in them.
There are other bacteria that can withstand very high temperatures, such as those living around boiling water springs in different parts of the globe. In Yellowstone National Park, Wyoming, there are more than 10,000 springs of this type, in which the water temperature is close to 100 degrees centigrade, however, in the rocks bathed by boiling water, live and multiply bacteria in an elongated form.
Endospores of some bacterial species can withstand boiling for several minutes, a test that would destroy most other life forms.However, even the most resistant microorganisms are unable to grow and multiply and lack water, although many of them can withstand desiccation.
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