544 Journal of A griculiural Research voi. xvni, no. io 



Growth is good in the usual culture media, though the peptone-beef 

 media are less favorable for growth and retention of vitality than potato, 

 milk, or Uschinsky's solution. 



CULTURAL CHARACTERS 



Agar poured plates. — On peptone-beef agar the colonies become 

 visible in about two days at room temperature and if well isolated reach 

 a diameter of from 6 to lo mm. in six days. The colonies are white or 

 rather like boiled starch and translucent. After several days the color is 

 greenish white. The bacteria in mass on a white background are yellow- 

 ish green. The medium immediately surrounding the colonies becomes 

 greenish, and this color eventually spreads over the whole plate. A 

 single colony greens about one-fourth of an ordinary plate. The texture 

 is at first soft and tender, and the colonies coalesce readily. If the plate 

 is tipped, the colonies overflow the lower margin. Later the growth is 

 thicker but not viscid. The colonies are circular, margins entire and defi- 

 nite, surface shining and smooth, with age occasionally slightly con- 

 toured, finally drying to a whitish film as transparent as the dry agar 

 medium. A characteristic interior structure is the presence of numerous, 

 tiny striae concentrically arranged. Sometimes these are coarser, more 

 " fish-scale" in character. Only rarely have colonies occurred with " fish- 

 scale" marks predominating (see PI. 63, B). More often the "fish-scale" 

 marks have been observed at the margin of colonies. This coarse 

 marking rapidly changes into the finer lines termed "striae." The colo- 

 nies which show these " fish-scale " markings are extremely thin and trans- 

 parent. The striations usually disappear after six or seven days, though 

 thev have been observed in some cases in colonies 2 weeks old (PI. 63, C). 

 Oblique light is necessary for examination of these internal markings. 

 In reflected or direct transmitted light, colonies often show a marginal 

 band more opaque than the centers (PI. 63, D). Buried colonies are dense 

 and opaque and more or less irregular in shape. 



The usual type of colony is best illustrated by Plate 63, A, E, shown 

 under oblique lighting. Slight diversities in colony character seem to 

 be caused by various factors such as moisture content of medium, degree 

 of acidity or alkalinity of medium, temperature, length of time in artificial 

 media, etc. 



Whey agar. — Formula: 1,000 cc. whey, 300 cc. water, 15 gm. agar 

 flour, 15 gm. peptone, 15 gm. cane sugar, 3 gm. gelatin. Colonies smaller 

 but thicker than on beef agar. At first almost hemispherical, trans- 

 lucent, and with pearly luster. The smooth surface becomes slightly 

 contoured, and after four weeks the colony looks like a miniature rugged 

 mountain. Buried colonies are translucent and larger than in beef agar, 

 and the green stain is less conspicuous. 



Potato agar plus i per cent dextrose. — The organism grows well 

 on this medium, forming thick, almost opaque, greyish white colonies. 



