134 GENERAL PHYSIOLOGY 



Temperature. Temperature has a profound influence 

 upon the lower as well as on the higher forms of life. Every 

 organism becomes habituated or attuned to certain temper- 

 atures. If the functions of life become adjusted to this par- 

 ticular temperature, any considerable variation affects these 

 functions. An increase of temperature within certain limits 

 increases the activity of the cell. The power of absorption 

 is increased and the excretions are accelerated, so that the whole 

 life process becomes more active. Variations from this tem- 

 perature, either above or below, decrease the activity. Be- 

 yond a certain limit functional activity ceases and growth stops, 

 and finally certain marked variations render the existence of 

 the organism impossible. The temperature limits within which 

 the life of the bacteria is possible are wide, in a general way 

 extending from the temperature of boiling water down to 

 practically absolute zero. The temperature limits within 

 which functional activities occur are very much narrower and 

 for most forms of life are between zero and a temperature 

 slightly above that of the animal body. In considering the 

 effect of temperature on bacteria, there are several cardinal 

 points which must be taken into consideration. There is the 

 maximum temperature, which is the highest temperature at 

 which the bacteria are able to carry on their life processes. 

 The optimum temperature is that temperature at which the 

 bacteria grow best. The minimum temperature is the lowest 

 temperature at which the bacteria are capable of growing, and 

 the thermal death point is that temperature at which bacteria 



