58 



ESSENTIALS OF BACTERIOLOGY. 



CHAPTER XI. 



THE GROWTH AND APPEARANCES OF COLONIES. 



FIG. 30. 



Naked eye appearances of colonies. 



Macroscopic. Depending greatly upon the temperature of 

 the room, which should be about 

 65 C., the colonies develop so as 

 to be visible to the naked eye in 

 two to four days. Some require 

 ten to fourteen days, and others 

 grow rapidly, covering the third 

 dilution in thirty-six hours, The 

 plate should be looked at each day. 

 The colonies present various ap- 

 pearances, from that of a small dot, 

 like a fly speck, to that resembling 

 a small leaf. Some are elevated, 

 some depressed, and some, like cholera, cup-shaped, umbilicated. 

 Then they are variously pigmented. Some liquefy the gela- 

 tine speedily, others not at all. The appearances of a few are 

 so characteristic as to be recognized at a glance. 



Microscopic. We use a low-power lens, with the abbe nearly 

 shut out, that is the narrowest blender. The stage of the 

 microscope should be of such size as to carry a culture plate 

 easily upon it. 



The second dilution or third plate is usually made use of, that 

 one containing the colonies sufficiently isolated. 



These isolated ones should be sought for, and their appearances 

 well noticed. 



There may be two or three forms from the same germ, the 

 difference due to the greater or less amount of oxygen that they 

 have received, or the greater or less amount of space that they 

 have had to develop in. 



The microscopic picture varies greatly ; now it is like the 

 gnarled roots of a tree, and now like bits of frosted glass ; the 

 pictures are very characteristic, and the majority of bacteria 

 can be told thereby. (Fig. 31.) 



