160 LABORATORY METHODS OF 



teria serve a useful purpose in nature by breaking up 

 the complex substances that we find in nature into 

 simpler ones. 



The reaction of the medium is of importance, since 

 many bacteria will not grow on any but an acid me- 

 dium, and all but a very few require an alkalin me- 

 dium. 



Moisture is the next to consider. All bacteria re- 

 quire moisture; but some can live with less than oth- 

 ers; some can stand drying for several days and then 

 remain vital when placed in a suitable place for 

 growth (for an example, take the anthrax). 



The relation of bacteria to the gases of the atmos- 

 phere is another important consideration. Some can 

 live without the oxygen, while others cannot live even 

 a short while without it; still another variety can live 

 with or without the presence of air. 



Temperature is the next to be considered. The 

 point where the bacteria will grow best is called the 

 optimum temperature. This is usually the same as 

 that of summer weather. The temperature in which 

 they grow with the greatest difficulty is called the 

 minimum temperature. 



MEDIA. 



1. Take beef extract 3 grams 



2. Peptone 10 grams 



