THE STUDY OF COLONIES. 145 



here nothing particularly characteristic will present, 

 there the point may resolve itself into a mass having 

 somewhat the appearance of a little pellicle of raw cot- 

 ton. All these differences, and many more, aid us in 

 saying that these objects must be different in their 

 nature. With a pointed platinum needle take up a 

 bit of one of these small islands, prepare it for micro- 

 scopic examination (see chapter on Stained Cover-slip 

 Preparations), and examine it under the high-power oil- 

 immersion objective, with access of the greatest amount 

 of light afforded by the illuminator of the microscope. 

 The preparation will be seen to be made up entirely of 

 bodies of the same shape ; they will all be spheres, or 

 ovals, or rods, but not a mixture of these forms, if proper 

 care in the manipulation had been taken. Examine in 

 the same way a neighboring spot which possesses dif- 

 ferent naked-eye appearances, and often it will be found 

 to consist of bodies of an entirely different appearance 

 from those seen in the first preparation. 



These spots or islands on the surface of the plates are 

 colonies of bacteria, differing severally, not only in their 

 gross appearances, the one from the other, but, as our 

 cover-slip preparations show, in the morphological char- 

 acteristics of the individual organisms composing them. 



If from one of these colonies a second set of plates be 

 prepared, the peculiarities which were first observed in 

 it will be reproduced in all of the new colonies which 

 develop ; each will be found to consist of the same 

 organisms as the colony from which the plates were 

 made. In other words, these peculiarities are constant 

 under uniform conditions. 



The appearance of the colonies developing from 

 all organisms is regulated by their location in the 



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