CHAPTER VIII. 



THE ISOLATION AND CULTIVATION OF BACTERIA. 



Cultivating bacteria. As bacteria are omnipresent in 

 external nature, it is difficult to procure any material such 

 as soil, water, etc., which does not contain several species 

 or varieties of these organisms. The isolation of bacteria 

 means the separating of the different kinds of organisms so 

 that there is but one species of bacteria present which can 

 be cultivated on different media and the nature of its growth 

 determined. 



The cultivation of bacteria is much like that of garden 

 plants. In the growth of lettuce, for example, to determine 

 the nature of the developed plant all other plants and weeds 

 that grow up immediately around it are removed. So in 

 isolating and cultivating the bacillus of tetanus from the 

 soil it is first necessary to get it separated from all other 

 bacteria. 



The growth of Bacillus tetani alone in a tube of bouillon 

 would be a pure bouillon culture of that organism. 



Requirements of bacteria. In the artificial cultivation 

 of bacteria, or in their multiplication in nature, a number of 

 factors are necessary, such as food, moisture, temperature, 

 and to a certain extent, light. The extent of their develop- 

 ment and their effect upon the culture medium, host, or 

 surroundings depend upon and vary with these biological 

 requirements or life conditions. 



Food supply. The food for bacteria must be of such a 

 nature and in such a condition that the bacteria can as- 

 similate it. As a rule, they require organic matter, although 

 some species can thrive on inorganic elements and com- 

 pounds. Again, the food must be of suitable chemical reac- 

 tion. For most bacteria it must contain nitrogen. Some 

 species require carbo-hydrates. Unless the food is in a suit- 

 able condition the bacteria can not multiply. This is an im- 



