42 ESSENTIALS OF BACTERIOLOGY. 



Positive. Negative. 



Tetanus Bacillus, Friedlander's Bacillus, 



Diphtheria Bacillus, Plague Bacillus, 



Pneumococcus, Diplococcus intracellularis, 



Streptococcus, Gonococcus, 



Staphylococcus, Koch-Weeks' Bacillus, 



Cocci of the urethra. Conjunctivitis Bacillus of Morax. 



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 microscopical ex- 

 amination or animal experimentation. 



To properly develop bacteria we supply as near as possible 

 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. If we place our nutrient material 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. To thoroughly 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 con- 

 tainers, the entrance of foreign germs. 



Disinfectants. Corrosive sublimate (bichloride of mercury), 

 which is the most effective agent we possess, cannot be gene- 

 rally used because it renders the soil unproductive and therefore 



