PRACTICAL BACTERIOLOGY. 



or less slimy masses -wifcli irregular outlines. These 

 masses are generally whitish or yellowish, being rarely 

 of any other colour. They are colonies of bacteria, 

 which, if they are situated sufficiently far apart from 

 each other, present small pure cultures of the different 

 species. While the slices of turnip were lying in 

 contact with the air, bacteria germs fell upon them. 

 These, if the soil suits them, develop at the spots, 

 where they fall, into small colonies, which remain 

 isolated upon the firm medium, and only can become 

 mixed with other bacteria, if neighbouring colonies, 

 in consequence of their continued growth, touch each 

 other. 



Occasionally, however, it may happen that two germs 

 of different kinds fall upon the same spot, and that 

 thus the resulting colony is impure from the outset. 

 As a rule, however, it may be taken for granted, that 

 colonies which are pure at the beginning are obtained 

 by this method, and these afford us the original 

 material for the pure cultures to be described later. 

 Generally colonies of moulds (especially of the Penicil- 

 lium glaucum, or of species of the genera Aspergillus 

 and Mucor) develop amongst the bacteria colonies ; 

 these are easily to be recognised, as it can be readily 

 seen with the magnifying glass, or indeed with the 

 naked eye, that they are composed of long threadlike 

 hyphse. Later on, these hyphae raise themselves 

 above the surface, and develop reproductive organs. 



