44 ESSENTIALS OF BACTERIOLOGY 



CHAPTER VII 

 METHODS OF CULTURE 



Artificial Cultivation. The objects of cultivation are to 

 obtain germs in pure culture, free from all foreign matter, 

 isolated, and so developed as to be readily used either for 

 microscopic examination or animal experimentation. 



To develop bacteria properly we supply, as nearly as possi- 

 ble, the conditions which hold for the especial germ in nature. 

 With the aid of solid nutrient media the bacteria can be easily 

 separated, and the methods are nearly perfect. 



Sterilization of Cultures. If we place our nutrient mate- 

 rial in vessels that have not been properly disinfected, we will 

 obtain growths of bacteria without having sown any. 



If we have thoroughly cleaned our utensils and then not taken 

 care to protect them from further exposure, the germs we have 

 sown will be effaced or contaminated by multitudes of others 

 that are constantly about us. We, therefore, have two neces- 

 sary precautions to take: 



First, thoroughly to clean and sterilize every object that 

 enters into, or in any way comes in contact with, the culture. 



Second, to maintain this degree of sterility throughout the 

 whole course of the growth, and prevent, by proper containers, 

 the entrance of foreign germs. 



Disinfectants. Corrosive sublimate (bichlorid of mercury), 

 which is the most effective agent we possess, cannot be generally 

 used because it renders the soil unproductive, and, therefore, 

 must be employed only in washing dishes, to destroy the old 

 cultures. Even after washing a few drops of the solution may 

 remain and prevent growth, so that one must be careful to have 

 the glassware that comes in contact with the nutrient media 

 free from the sublimate. 



Heat. Heat is the best agent we possess for general use. 

 Dry heat and moist heat are the two forms employed, but these 

 differ greatly in effectiveness. Thus Koch found that while 



