QUALITATIVE BACTERIOLOGICAL ANALYSIS. 141 



Agar-plates. Incubated at 37 C. show exceedingly rapid 

 and characteristic growth. A single colony spreads in thirty- 

 six hours as a thin irregular dendritic film, covering almost the 

 whole surface of the plate. The film does not thicken on 

 further incubation. 



Agar-fitreak culture. Growth is very rapid both at 37 C. 

 and 20 C. Even at the latter temperature the whole surface 

 of the tube is covered in twenty-four hours by a thin homo- 

 geneous semi-transparent greyish film, advancing at the edge by 

 irregular processes. On the second day the growth is somewhat 

 thicker ahd whiter, and has reached its full development. There 

 is a scanty development of gas bubbles in the depth of the 

 agar-agar, but no odour of putrefaction is ever perceptible. 



Potato. Grows rapidly, forming a slimy layer of a yellowish- 

 grey colour. 



Broth. In twenty-four hours the broth is turbid, and in a 

 few days a slight film is present on the surface and a yellowish- 

 white deposit at the bottom of the tube. In a week there is a 

 marked putrefactive odour. Tested in eleven days no trace of 

 indol reaction was obtained. 



Mill:. Grows without producing any change in this medium. 



Micrococcus Aurora. 



Source. Found in fresh sewage from St. Bartholomew's 

 Hospital. 



Form and Arrangement. Slightly oval cocci, 0*7 to 0'8 ju in 

 diameter, often as diplococci separated by a cleft, rarely in 

 short chains of three or four elements. In broth cultures the 

 cocci are often arranged in irregular packets. 



Motility. Not motile. 



Gelatine Plates. Colonies first appear on the third day, 

 minute and circular, not yet pink in colour. Under the micro- 

 scope they appear granular and slightly irregular in outline. 

 On the fifth day the surface colonies are less than 0*5 mm. in 

 diameter, circular, prominent, and pinkish. After a week the 

 largest colonies are 0*7 mm. in diameter, those in the depth 

 0'25 mm., and of a pale pink tint. Later the colonies attain a 

 diameter of 1 to 1'5 mm., and liquefaction slowly occurs after 

 two to three weeks. 



