THE CULTIVATION OF BACTERIA. 8l 



less, they will not rise from the surface of the moist culture- 

 medium, nor drop from the needle during its transit, if proper 

 care be exercised. They may be thrown into the air if the 

 needle be allowed to sputter in the flame, or is roughly shaken 

 about. 



It must be remembered also that such organisms as moulds develop spores 

 which are formed on filaments elevated above the surface of the medium and are 

 easily detached. 



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 bichloride 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 laboratory. 



To maintain their vitality bacteria need to be transplanted 

 from time to time from the medium in which they are culti- 

 vated to fresh medium; the frequency with which this trans- 

 plantation is necessary varies greatly with different species. 

 When transplanted from one tube to another the bacteria should 

 be examined with the microscope both in the original tube and in 

 the resulting growth in order to check the purity of the culture. 

 Bacteria differ greatly in the ease with which they may 

 be cultivated artificially. Many of them grow on culture- 

 media with difficulty when first taken from the animal body, 

 or when first transplanted from one sort of medium to a differ- 

 ent one. But they become accustomed to such changes of 

 conditions and frequently may be propagated easily on the new 

 medium. This is especially true of bacillus tuberculosis. 



From what has just been said, it is evident that some bacteria 

 flourish better on one culture-medium than on another. The 

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