16 



Dairy Bacteriology. 



the manner in which it acts toward gelatin. In order to 

 make sure that the seeding in not too copious so as to in- 

 terfere with continued study, an attenuation is usually 

 made. This consists in taking a drop of the infected gel- 



Fio. 8. Profile view of gelatin plate culture ; , a liquefying form that dissolves 

 the gelatin; c and </, surface colonies that do not liquefy the gelatin. 



atin in the first tube, and transferring it to another tube 

 of sterile media. Usually this operation is repeated again 

 so that these culture plates are made with different 

 amounts of seed with the expectation that in at least one 

 plate the seeding will not be so thick as to prevent further 

 stady. For transferring the culture a loop made of plat- 

 inum wire is used. By passing this through a gas flame, it 

 can be sufficiently sterilized. 



To further study the peculiarities of different germs, the 

 separate colonies are transferred to other sterile tubes of 

 culture material and thus pure cultures of the various 

 germs are secured. These cultures then serve as a basis for 

 continued study and must be planted and grown upon all 

 the different kinds of media that are obtainable. In this 

 way the slight variations in the growth of different forms 

 are detected and the peculiar characteristics are determined, 

 so that the student is able to recognize this form when he 

 meets it again. 



These culture methods are of essential importance in 

 bacteriology, as it is the only way in which it is possible 

 to secure a quantity of germs of the same kind. 



