316 BACTERIOLOGY. 



comma and spiral shapes may entirely disappear, their 

 place being taken by irregular involution forms that 

 present every variety of outline. (See Fig. 61.) In 

 this stage they take on the staining very feebly, and 

 often not at all. 



Oidtural peculiarities. On plates of nutrient gelatin 

 that have been prepared from a pure culture of this 

 organism and kept at a temperature of from 20° to 22° 

 C, development can often be observed after as short a 

 period as twelve hours, but frequently not before sixteen 

 to eighteen hours. This is especially true of the first 

 or " original " plate, containing the largest number of 

 colonies. At this time the plate will present-to the 

 naked eye an appearance that has been likened to a 

 ground-glass surface, or to a surface that has been 

 stippled with a very finely pointed needle, or one 

 upon which very fine dust has been sprinkled. This 

 appearance is due to the presence of minute colonies 

 closely packed together upon the surface of the gelatin. 

 In the depth of the gelatin can also be seen, closely 

 packed, small points, likewise representing growing 

 colonies. As growth progresses liquefaction occurs 

 around the superficial colonies, and in consequence this 

 plate is usually entirely liquid after from twenty-four 

 to thirty hours; the developmental phases through 

 which the colonies pass cannot, therefore, be studied 

 upon it. 



On plates 2 and 3, where the colonies are more widely 

 separated, they can be seen after twenty-four to thirty 

 hours as small, round, or oval, white or cream-white 

 points, and when located superficially there can be 

 detected around them a narrow transparent zone of 

 liquefaction. As growth continues, this liquefaction 



