CHAPTER II. 

 INFLUENCE OF TEMPERATURE. 



Temperature, as well as moisture, is one of the most important factors 

 of life. It is so important that the most highly developed animals pro- 

 tect themselves by a very complicated mechanism of regulation against 

 changes of temperature; the life processes of such animals will take 

 place at a temperature nearly constant from birth to death. This neces- 

 sitates a distinct difference in the metabolism of warm-blooded animals 

 and all other organisms. The metabolism of the warm-blooded animals 

 takes place at a constant temperature. The required amount of food 

 is constant except for the part that is used for heating the body; at lower 

 temperatures, more heat-producing material is used and the result is that 

 warm-blooded animals require more food, the lower the temperature. 

 All other organisms, reptiles as well as bacteria, have the temperature 

 of their environment and the decrease of temperature will decrease the 

 intensity of metabolism as it retards any other chemical process. The 

 lower the temperature, the less food is required by all lower organisms. 



There are, of course, limits to the favorable influence of high tempera- 

 ture. Growth and metabolism of microorganisms will increase with a 

 rising temperature to a certain point, called the optimum temperature, 

 and beyond this point the rate of growth will fall off rapidly and soon 

 cease entirely. The highest temperature at which growth can take place 

 is called the maximum temperature. Correspondingly, the minimum 

 temperature of an organism is the lowest point at which growth can take 

 place. 



THE OPTIMUM TEMPERATURE which allows the fastest growth will be 

 quite different for different species. Groups of bacteria are known which 

 develop only at very high temperatures and others for which room tem- 

 perature is too high. The temperature requirement is largely dependent 

 upon the natural habitat of the organisms. The bacteria of the polar sea 

 and of a lagoon near the equator will very probably have different 

 optimum temperatures because of the acclimatization and selection 

 which has been taking place for centuries. 



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