CHAPTER II 

 INFLUENCE OF TEMPERATURE 



Temperature, as well as moisture, is one of the most important fac- 

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

 protect 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 

 causes the metabolism of warm-blooded animals to be different from 

 that of 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 at lower tempera- 

 ture. All other organisms, reptiles as well as bacteria, have the tem- 

 perature 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- 

 tures. Growth and metabolism of microorganisms will increase with 

 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 mini- 

 mum 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 

 temperature is too high. The temperature requirement is largely de- 

 pendent upon the natural habitat of the organisms. The bacteria of 



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