120 BACTERIOLOGY. 



Here nothing 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 it for 

 microscopic examination (see chapter on stained cover- 

 slip preparations), and examine it under the high power 

 oil-immersion 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 neighboring spot 

 which possesses different naked-eye appearances, and it 

 will often 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 all of the new set 

 of colonies which develop ; each will be found to con- 

 sist of the same organisms as the colony from which the 

 plates were made. In other words, these peculiarities 

 are constant under constant conditions. 



With all organisms differences in the appearance of 

 the colonies depending upon their location in the medium 



