THE STORY OF THE BACTERIA. 2Q 



He calculates that the bacteria which he has 

 thus put into the large flask of water will have 

 been so much diluted and separated that, if he 

 now dips a needle into this water, or takes out 

 a small drop, and rinses it off into one of the 

 tubes of beef-tea, and does this for each one 

 of the several beef-tea tubes which he has pre- 

 pared, into some of them he will have intro- 

 duced, small as they are, only one single indi- 

 vidual bacterium. 



He now sets his beef-tea tubes away in a 

 warm place where no accidental contamination 

 can occur, and lets them stand until the fluid 

 begins to get turbid. Now, by a careful mi- 

 croscopical examination he can tell whether 

 one or several forms of bacteria are growing 

 in his tubes, and if in any of them only one 

 form is present he has succeeded, and has what 

 he calls a culture of some particular bacterial 

 species. This he can study at his leisure, plant 

 and replant it in fresh beef-tea tubes, and find 

 out to a certain extent what its habits are, what 

 new chemical substances it produces as it feeds 

 itself from the beef-tea, etc. 



But this is a long and wearisome process 

 and somewhat uncertain^ in its results too, 



