BACTEKIA AND THEIE RELATION TO DAIRYING. 19 



bacteria that the colonies go over into one another, differ- 

 ent nutritive substrata may be inoculated with a part of 

 the different colonies, and pure cultures are in that way 

 obtained of the various organisms; provided, however, that 

 the whole process has been conducted with due care and 

 dexterity. When the various species of bacteria found in 

 the liquid have been isolated in this manner, they are 

 grown in different substrata to study their manner of 

 growth and effects. The determination of the bacterial 



FIG. 18. 



a, glass plate; 6, congealed gelatine, in which maybe found all kinds of colo- 

 nies; the colony at c liquefies the gelatine, the others do not. The ramified 

 colonies consist of moulds, the others of bacteria. 



contents of water or milk is as a rule conducted according 

 to the method here given. By this and other bacteriologi- 

 cal operations it is, however, not enough to make only a 

 single examination ; a number of control cultures must 

 always be made. 



Unfortunately all bacteria cannot Be isolated and 

 grown in this easy manner; but the method of procedure 

 in other cases cannot here be explained in detail, and in- 

 terested readers are referred to the text- books already 



