METHODS OF CULTURE. 39 



General Double Staining for Sections. 

 I. Stain (watery dyes) . . . 10 to 15 minutes. 

 II. Acetic acid and water (1 to 4) . minute. 



III. Alcohol 2 to 3 minutes. 



IV. Contrast stain, usually picro-car- 



mine or eosiu . . . . 2 to 3 minutes. 



Y. Alcohol i minute. 



VI. Clove oil. Canada balsam. 



Instead of coloring with the contrast last, it can be used first, 

 then alcohol one-half minute, followed by the bacteria stain, acid 

 water, alcohol, clove oil, and Canada balsam in succession. 



The stains for special bacteria will be given when treating of 

 the same. 



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. 



