METHOD OF ISOLATION. 93 



same results at will from mixture of diiferent species of 

 bacteria when found together under other conditions ? 

 It was plain that the organisms were to be distinguished 

 primarily, the one from the other, only by the structure 

 and general appearance of the colonies growing from 

 them, for by their morphology alone this is impossible. 

 What means might be devised, then, for separating the 

 individual members of a mixture in such a way that 

 they would remain in a fixed position, and be so widely 

 separated, the one from the other, as not to interfere 

 with the production of colonies of characteristic appear- 

 ance, which would, under favorable conditions, develop 

 from each individual cell ? 



If one take in the hand a mixture of several kinds of 

 flower seeds and attempt to separate the mass into its 

 constituents by picking out the diiferent grains, the 

 task is tedious, to say the least of it; but if the handful 

 of seeds be thrown upon a large flat surface, as upon a 

 table, the grains become widely separated and the matter 

 is considerably simplified ; or, if sown upon proper soil, 

 the various grains will germinate and develop into plants 

 of entirely diiferent characteristics, by which they can 

 readily be recognized as distinct species. Similarly, if 

 a test-tube of decomposed bouillon be poured upon a 

 large, flat surface, the individual bacteria in the mass are 

 much more widely separated, the one from the other, 

 than they were when the bouillon was 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 impossible by this 

 means to pick out the individuals from the mixture. 



If, however, some substance could be found which 



