PRINCIPLES IN METHODS OF ISOLATION 105 



moist objects from the air, and as the cell grows and mul- 

 tiplies it forms these circumscribed patches or "colonies" 

 as they are called. 



* The question that then presented itself was: If from a 

 mixture of organisms floating in the air it is possible in this 

 way to obtain in pure cultures the component individuals, 

 what means can be employed for obtaining the same results 

 at mil from mixture of different 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 appear- 

 ance of the colonies growing from them, for by their mor- 

 phology alone this is impossible. What means might be 

 devised, then, fpr 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 charac- 

 teristic appearance, which would, under favorable condi- 

 tions, 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 con- 

 stituents by picking out the different 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 con- 

 siderably simplified; or, if sown upon proper soil, the various 

 grains germinate and develop into plants of entirely different 

 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 wfts 



