PRINCIPLES IN METHODS OF ISOLATION 



103 



in the tube; but they are in a fluid medium; and there is 

 no possibility of their either remaining separated or of 

 their colonizing under these conditions, so that it is impos- 

 sible by this means to pick out the individuals from the 

 mixture. 



FIG. 14 



Showing certain macroscopic characteristics of colonies. Natural size. 



If, however, some substance can be found which possesses 

 the property of being at one time fluid and at another time 

 solid, and which can be added to this bouillon without in 

 any way interfering with the life-functions of the bacteria, 

 then, as solidification set in, the organisms would be fixed 



