PLATE METHOD OF KOCH. 69 



It was plain that the organisms were to be distin- 

 guished, 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 impossibly. 



What means could 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 inter- 

 fere with the production of colonies of characteristic 

 appearance, which would, under the proper conditions, 

 develop from each individual cell? 



If one takes in the hand a mixture of barley, rye, 

 corn, oats, etc., and attempts to separate the mass into 

 its constituents by picking out the different grains, much 

 difficulty is experienced ; but if the handful of grain be 

 thrown upon a large flat surface, as upon a table, the 

 grains become more widely separated and the task is 

 considerably simplified; or, if sown upon proper soil 

 the various grains will develop into groM'ths of entirely 

 difi^erent external appearance by which they can readily 

 be recognized as unlike in nature. Similarly, if a test- 

 tube of decomposed bouillon be poured out upon a large 

 flat surface, the individual bacteria in the mass are very 

 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 forming 

 colonies under these conditions, so that it is impossible by 

 this means to pick out the individuals from the mixture. 



If, however, it is possible to find some substance 

 which possesses the property of being at one time fluid 

 and at another time solid, which can be added to this 

 bouillon without in any way interfering with the life- 



4* 



