general bacteriology 
33 
which produce disease, that is, are pathogenic, while the 
saprophytes live on dead matter and are of greatest value 
in the world’s economy in breaking up the organic matter 
through the processes of fermentation and putrefaction. 
X. Mutual Relations of Bacteria 
It is evident that in many cases several different bac¬ 
teria must live in the same place, or, in other words, the 
same surrounding must be favorable to several species. 
This possibility of several bacteria living and multiplying 
in the presence of each other is spoken of as symbiosis 
(from Greek syn, meaning with, and bios, meaning life), 
as exemplified by diphtheria and streptococci. Symbiosis 
is not so frequent, however, as the opposite fact—namely, 
the impossibility of one organism living in the presence 
of another—a condition which is known as antagonism 
(from Greek antagonisma, meaning struggle) ; examples 
of bacterial antagonism are gonococcus and bacillus pyocy- 
aneus, plague bacillus and streptococci, etc. 
XI. Relations of Bacteria to Physical Environment 
Temperature. —Bacteria, like other living beings, have 
their minimum (lowest), maximum (highest), and opti¬ 
mum (the best) temperature at which they will live, grow 
and multiply. 
For the large majority of the bacteria the optimum 
temperature is 37.5° C.; on the other hand, there are 
numerous bacteria in the water which grow at 20° C. 
Individual organisms have their limits, these varying 
with the environment adopted by them through many gen¬ 
erations; for example, the bacillus of the avian (bird) 
tuberculosis grows at 41° to 42° C. and can not grow 
at 37.5° C., while the bacillus of human tuberculosis grows 
best at the latter and will not grow at the former tempera- 
