134 BACTERIOLOGY. 



here nothing particularly characteristic will present, 

 there the point may resolve itself into a little mass 

 having somewhat the appearance of a very small pellicle 

 of raw cotton. All these differences, and many more, 

 aid us in saying that these little points must be different 

 in their nature. With a pointed platinum needle take up 

 a bit of one of these little 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 has been taken. Examine in 

 the same way a neighboring spot which possesses dif- 

 ferent naked-eye appearances, and it will often 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 out- 

 ward 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 this colony will be reproduced in all of the new set 

 of 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 like conditions. 



With all organisms differences in the appearance of 

 the colonies dependent upon their location in the me- 



