462 BACTERIOLOGY. 



growing readily at a temperature from 18 to 20 C., 

 but best at 37, in milk, bouillon, and other liquid 

 media, and in nutrient gelatin or agar, accompanied by 

 liquefaction of the gelatin. 



Growth on Gelatin. Grown on gelatin plates it 

 develops, at room-temperature within forty-eight hours, 

 punctiform colonies, which, when examined under a 

 low-power lens, appear as circular disks of a pale brown 

 color, somewhat darker in the centre, and surrounded 

 by a smooth border. The colonies grow rapidly. The 



FIG. 59. 



Staphylococcus. X 1100 diameters. 



appearance of the growth is most characteristic. Im- 

 mediately surrounding the colonies, which are of a pale 

 yellow color, there is a deepening of the surface of the 

 gelatin, due to its liquefaction. By suitable light a 

 number of these shallow depressions with sharply de- 

 fined outlines may be seen on the gelatin plate, having 

 a diameter of from 5 to 10 mm., in the centres of which 

 lie the yellow colonies. Later, the liquefaction becomes 

 general, the colonies running together. In stick cul- 

 tures in gelatin a white confluent growth at first appears 



