Artificial Cultivation of Bacteria. 21 



Handling of bacteria. The bacteria are handled in 

 the laboratory and are transferred from one culture 

 tube to another containing fresh food by means of small 

 platinum wires inserted in glass handles. These wires 

 are rendered germ free by heating them in a flame be- 

 fore they are used. By keeping the culture tubes 

 plugged with cotton, by careful use of the inoculating 

 needle, and by using care at every step, the bacteriolo- 

 gist works with the most dangerous disease-producing 

 organisms without danger to himself. 



Use of experimental animals. In the study of the 

 disease-producing or pathogenic bacteria, it frequently 

 becomes necessary to use for inoculation purposes small 

 animals, such as guinea pigs, rabbits, white mice, and 

 rats. Some forms of bacteria can not grow on any of 

 the artificial media but may develop in the bodies of 

 animals, so that animal inoculation becomes a necessity 

 in determining whether any particular kind of organ- 

 ism is able to produce disease or not. 



Incubation of bacteria. Many of the bacteria have 

 acquired parasitic properties and grow naturally only 

 in the bodies of animals. Such is the case with the tu- 

 bercle bacillus. If such types are to be artificially 

 propagated, the cultures must be kept under conditions 

 simulating the animal body. Hence incubators to main- 

 tain the cultures at the same temperature as the animal 

 body are more or less essential in bacteriological work. 



