374 AGEICULTUEAL AND INDUSTRIAL BACTERIOLOGY 



nodules secured under aseptic precautions from infected 

 animals over the surfaces of solidified blood serum or egg 

 medium. It is sometimes necessary to keep at blood heat 

 for one to two weeks before visible growth develops. When 

 the organism is not in pure culture as is the case in milk, 

 feces, etc., isolation is frequently attended with difficulty. 

 It may be accomplished by inoculating the material from 

 which the culture is to be secured into a suitable animal 

 such as a guinea pig, allowing the disease tuberculosis to 

 develop, and securing the organism in pure culture from 

 the lesions. It may also easily be secured by dissolving the 

 organic material and other bacteria in antiformin, washing 

 and inoculating a culture tube. 



After cultivation in the laboratory the organism will 

 grow somewhat more readily upon culture media, particu- 

 larly those which contain blood serum, egg or similar 

 proteins or to which glycerol has been added. 



The colonies upon blood serum or upon glycerin agar 

 appear first as tiny grains barely visible to the naked eye. 

 In cultures where they grow readily, the colonies become 

 confluent and cover the surface of the medium with a dry, 

 wrinkled growth. In old cultures this may become creamy 

 or brown in color. In glycerin broth there is usually 

 formed a more or less heavy wrinkled scum which readily 

 sinks to the bottom when shaken. 



Organisms isolated from human sources usually adapt 

 themselves much more quickly and readily to culture media 

 than those from bovine and always grow much more luxuri- 

 antly. In typical cases it is not difficult to tell which strain 

 an organism belongs to by the differences in the growth 

 appearance. The bovine organism usually forms isolated 

 colonies while those from human cultures form a continuous 

 wrinkled growth over the surface of the medium. 



Physiological Characters. The organisms from human 

 and bovine sources grow best at blood heat and their growth 



