100 BACTERIOLOGY 



Here nothiDg particularly characteristic will present, 

 there the point may resolve itself into a little mass hav- 

 ing 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 a stained cover- 

 slip preparation (see chapter on cover-slip preparations) 

 from it, and examine it under the high power oil-immer- 

 sion objective, under 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 neighboriug spot which possesses different naked- 

 eye appearances, and it will be found to consist of bodies 

 of an entirely different appearance from those 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 at first observed in 

 this colony will be reproduced in the new set of colonies 

 which develop. In other words, these peculiarities are 

 constant under constant conditions. The colonies will 

 be found to consist of the same organisms as the colony 

 from which the plates were made, and colonies of no 

 other organisms will be present. 



With all organisms differences in the appearance of 



