284 MICROBIOLOGY 



crenated borders and a papillated center. When a pure cul- 

 ture is used for inoculation on slant agar, the colonies appear 

 in forty- eight hours, growing abundantly over the whole sur- 

 face and becoming confluent. All cultures grown on agar are 

 characteristic in being extremely dry and adherent to the 

 medium. In cover-glass preparations the bacteria are found to 

 be arranged in clumps. It grows .more slowly and not so 

 abundantly on glycerine agar as on agar. 



Gelatin. Gelatin at room temperature does not prove a 

 desirable medium for the organism. When incubated at 

 37.5 C. the growth is identical with that in bouillon. 



' Blood serum. On blood serum it grows more readily than 

 on any other of the media although the cultures are not so 

 characteristic as are those on agar. The growth is marked at 

 the end of forty-eight hours by the appearance. of small pin- 

 point colonies, which increase slowly until the tenth day, when 

 they have a diameter of 1 to 1.5 mm. The border is slightly 

 irregular with a dry, glistening, uneven surface of a color 

 varying from deep yellow to grayish white. The colonies ap- 

 pear to send off lines of growth extending below the surface, 

 and are surrounded by a cloudy zone which has to a greater 

 or less degree the color of the colony. This outward radiation 

 becomes more marked, until finally the contour of the colony is 

 entirely effaced. The property of chromogenesis varies greatly, 

 even under uniform conditions. The water of condensation 

 contains a copious sediment of small granules which give it the 

 tint of the colonies. 



Potato. On .potato the growth varies to a great extent. 

 This is probably due to variations in its acidity. On potato 

 with slight acidity a grayish white, slightly moist growth 

 spreads irregularly over the surface. In some cases it is 

 hardly visible to the naked eye, and, as a rule, it reaches its 

 maximum growth at the end of the second week. With an 

 acidity of 2.9 to 3.6 per cent no growth occurs, while the addi- 

 tion of a few drops of a 5% "sodium hydroxide solution to the 

 surface will cause the multiplication of the organisms. 



Bouillon. In bouillon a general turbidity occurs in the 



