342 VETERINARY BACTERIOLOGY 



heart blood or the intestines of an aborted fetus. Bang used a 

 medium consisting of nutrient agar, to which he added liquid gela- 

 tin and sterile liquid blood-serum. These tubes were inoculated 

 with suspected material, mixed well, and kept at blood-heat. 

 In the course of three days numerous colonies developed in a 

 definite stratum a few millimeters below the surface. As will be 

 noted under the discussion of physiology, the organism has an 

 unusual relationship to oxygen, and the amount of oxygen needed 

 for its development is to be found at the depth at which the colo- 

 nies form. These colonies are compact, rounded, or somewhat 

 irregular, sometimes showing a dense nucleus surrounded by a 



Fig. 141. Bacillus abortus (Nowak). 



lighter zone. When the organism is present in impure culture, 

 as in the vagina of the cow, other methods are necessary for its 

 isolation. Nowak has described a procedure which has proved 

 satisfactory in the hands of several investigators. Probably 

 simpler methods will be devised in time, but this appears to be the 

 best thus far developed. The material is smeared over the surfjice 

 of successive tubes of scrum agar or over the surface of this medium 

 in Petri dishes. These are allowed to stand for several days, and 

 the colonies which develop are marked, as they are not B. abortus. 

 The plates are then placed in a desiccator, whose cubic content 

 of air has been determined, and plates of agar thickly seeded with 

 Bacillus subtilis are introduced, so that about 16 sq. cm. of surface 



