52 PURE CULTURE OF BACTERIA 



platinum needle and transferred to various liquid media; 

 e.g. to broth or milk, in which an abundant pure growth 

 of the particular organism can be obtained. The form 

 and other features of the bacterium can then be studied, 

 as well as its effect on the medium. 



In addition to their development in liquids, it is usual 

 to make an examination of the growth of bacteria on the 



1234 



FIG. IQ. Diagram of common forms of stab-cultures. 



i, Filiform; 2, beaded ; 3, rhizoid or arborescent ; 4, beaded stab-culture 



of anaerobic organism. 



surface or deep within the substance of the solid gelatine 

 or agar media. For the latter purpose tubes of solid 

 media are inoculated by means of a platinum needle 

 dipped in a pure culture in broth, or in a colony isolated 

 on gelatine or agar, the needle being pushed deeply into 

 the substance of the solid medium and then withdrawn. 

 The colonies of the bacteria develop along the track of 

 the needle, forming a stab-culture (Fig. 19). The needle 

 may, on the other hand, be drawn lightly along the sur- 

 face of solid media in straight lines, and a streak- culture 

 obtained. The medium for the latter purpose may be 



