LABORATORY TECHNIC 41 



Japanese moss, agar-agar. These foodstuffs, called 

 media for short (sing., medium) are kept in test-tubes 

 or flasks. The worker may also spread into flat glass 

 plates (Petri plates) some of this stiffened broth in 

 order first to see in what form the germs will grow as 



FIG. 11. Showing certain macroscopic characteristics of colonies. 

 Natural size. (Abbott.) 



"colonies," and secondly, to see that only one kind of 

 colony, therefore only one kind of germ, is present 

 (Fig. 11). In other words, he wishes to know if his 

 culture be "pure." This means of obtaining a pure 

 culture depends upon the fact that from each single 



