CHAPTER IX. 



EFFECT OF TEMPERATURE UPON BACTERIA. 



IN judging the effect on bacteria of different agents 

 we have first to note the important fact that different 

 species of bacteria are differently influenced by the same 

 substances. Some bacteria thrive under conditions 

 which would destroy others, and they vary among 

 themselves in their powers of resistance to influences 

 which are deleterious to all. 



Further, any species of bacteria will resist better 

 when under favorable conditions than under unfavor- 

 able ones. Bacteria also in recent cultures withstand 

 injury better than those in old cultures, so long as they 

 have not entered into the spore form. A ccor cK n g to 

 the amount of injury they have suffered, bacteria may 

 be only lamed in some of their functions or they may 

 be totally destroyed. Their loss of function may be 

 only temporary or permanent. 



Every bacterial species makes certain demands on 

 the temperature of its culture media. Vegetative life 

 is possible within the limits of and 70 C. There 

 are some species, however, which grow at the lower and 

 others at the upper limit of these temperatures. The 

 maximum and minimum temperature for each indi- 

 vidual species lies about 30 C. apart. Bacteria have 

 been classified according to the temperatures at which 

 they develop, as follows : 



