68 .1 BacttrUd Spot of C(frt(s 



Cultural Characters. 



Nutrient agar colonies. The organism grows very rapidly on 

 nutrient agar and when first isolated from the tissues the speed with 

 which the colonies appear varies considerably ; after prehminary 

 cultivation however, more even results are obtained. The following 

 is a description of the development of typical colonies at 25° C. 



After 24 hours in thinly sown plates the colonies are 1 — 4 mm. in 

 diameter, they average 2 mm., and are round-irregular in shape; by 

 transmitted light translucent with a small opaque centre, pearly white 

 to bluish, yellowish by reflected light. Under the microscope the 

 colony is granular with a grumose centre, the granular margin being 

 composed of a swirling mass of actively motile rods. Submerged 

 colonies are minute opaque, mostly bi-convex. 



After two days the average diameter of the colonies has increased 

 to 4 mm., and some measure as much as 7 mm., they are coppery by 

 transmitted light with a bluish margin, straw yellow by reflected light. 

 There is a small opaque centre surrounded by a rather dense sub-opaque 

 ring and then b}' a translucent margin. Under the low power of the 

 microscope the central portion is grumose. the outer finely granular. 



Submerged colonies have increased somewhat in size and now have 

 the appearance of two or more lenticular bodies placed at different 

 angles, or of a single lenticular body with sub-spherical outgrowths. 



After three days the colonies average 5 — 6 mm. in diameter, the 

 largest are 10 mm., they are round-irregular, umbonate; Naples 

 yellow to buff yellow by reflected hght, coppery throughout by trans- 

 mitted light ; under the microscope they are much more dense than 

 before except at the edge, and the whole of the central part is grumose ; 

 there is no longer any motion visible with a low magnification. Sub- 

 merged colonies have increased in size up to I "iwi- 



After four days the colour has become mustard yellow and long 

 feathery crystals have made their appearance in the medium. 



There is usually no further change after the fifth day ; the colonies 

 then measure up to 15 mm. in diameter, the margin is entire or undulate, 

 and there are frequently two or three concentric rings. The surface 

 of the agar has become distinctly whitened especially in the immediate 

 vicinity of the colonies. 



The growth in this case does not become tough or leathery, it is 

 always creamy in consistency. 



