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 Jong as they 
have not entered into the spore form. According 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 0° 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 : 
