158 TECHNOLOGY OF BACTERIA. 



ture-fluid is poured upon glass slides, to which it 

 adheres when cool in the form of a semi-solid 

 layer. Upon this the mixed bacteria are dis- 

 tributed by means of a needle, the point of which 

 is lightly drawn across the surface, after having 

 been charged with seed by dipping it into the 

 stock-solution a biological analysis of which is 

 desired e. g. broken-down urine or beef tea. 

 The different micro-organisms are distributed by 

 this method along the track of the needle, and the 

 subsequent multiplication of each germ in situ, 

 when the slide has been left for a day or two in 

 the culture-oven, produces a little collection of the 

 particular species to which it belongs, which may 

 be recognized under the microscope or even by 

 the naked eye. 



A pure culture is obtained by inoculating a 

 sterilized culture-fluid with seed, transferred with 

 due precautions, from one of these little masses 

 formed along the track of the needle. 



Another method which suggests itself, and will 

 doubtless be found useful in certain cases, depends 

 upon the difference as to reproductive activity 

 manifested by different species of bacteria, and 

 upon the fact that a culture-medium, or conditions 

 as to temperature, favorable for the development 

 of one species may not be for another. By taking 

 advantage of these physiological peculiarities we 

 may succeed in excluding all but a single form, 

 by one or more culture experiments, notwithstand- 

 ing the fact that our stock was impure at the 



