THE CULTIVATION OF BACTERIA. 87 



If, by any accident, drops of infectious material should 

 fall upon a surface like the table, they should be covered 

 at once with bichloride of mercury solution i-iooo. A 

 good way is to cover the spot with a piece of blotting-paper 

 wet with the solution ; place a bell- jar over it and leave for 

 several hours. If infectious material should reach the hands 

 or clothing, they should be thoroughly soaked in the bichlo- 

 ride solution. When working with pathogenic bacteria it 

 is well to wash the hands in this solution and with soap 

 and water, as a routine procedure, before leaving the labor- 

 atory. 



To maintain their vitality bacteria need to be transplanted 

 from one tube to another occasionally; the time varies 

 greatly with different species. Many bacteria grow on cul- 

 ture-media with difficulty at the first inoculation, but hav- 

 ing become accustomed to their artificial surroundings, as 

 it were, they may be propagated easily afterward; this is 

 especially true of the bacillus tuberculosis. 



Some bacteria flourish better on one culture-medium than 

 another. The bacillus tuberculosis grows best on blood- 

 serum and glycerin-agar ; the bacillus of diphtheria grows 

 best on LofBer's blood-serum; the gonococcus on human 

 serum-agar. 



The virulence of most pathogenic bacteria becomes 

 diminished after prolonged cultivation upon media. Some- 

 times the virulence is lost very quickly, for example, the 

 streptococcus pyogenes and micrococcus lanceolatus of pneu- 

 monia. 



Incubators. Many bacteria flourish best at a tempera- 

 ture about that of the human body, 38 C. Some species 

 will grow only at this temperature. The pathogenic bac- 

 teria in particular, for the most part, thrive best at a point 

 near the body temperature. 



The incubator is a box made of copper, having double 



