368 BACTERIOLOGY. 



seen in small groups of three or four, lying together in 

 such a way as to have their long axes nearly parallel to 

 one another. (See Fig. 71.) 



In old cultures in which development has ceased it 

 undergoes degenerative changes, and the characteristic 

 comma and spiral shapes may entirely disappear, their 

 place being taken by irregular involution-forms that 

 present every variety of outline. (See Fig. 72.) In 

 this stage they take on the stain very feebly, and often 

 not at all. 



Cultural 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 stip- 

 pled with a very finely pointed needle, or one upon 

 which very fine dust has been sprinkled. This appear- 

 ance 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 



