RELATION TO ENVIRONMENT 



137 



are subjected to extremes of cold, such as may now readily 

 be obtained by the use of liquid air, it has been found by 

 Ravenel, McFayden, and others that they may live for long 

 periods of time and, indeed, may be little changed. It is 

 to be understood in all of these cases that some individuals 

 readily succumb but that certain others persist, and this is 

 found to be the case whenever bacteria are brought into un- 

 favorable surroundings. There is great difference in the 

 powers of resistance towards any unfavorable conditions by 

 the different individuals in the same culture. 



Compared with other forms of life bacteria are more resist- 

 ant, as will be seen in the following table : 



Comparative Power of Various Organisms to resist Changes of Temperature 



The temperature of the bacterial cell varies with the tem- 

 perature of the surroundings in the same way that the temper- 

 ature of the cold-blooded animal varies. The bacteria are there- 

 fore spoken of as poikolothermic in contradistinction to those 

 organisms which have a constant temperature, as, for instance, 



