202 STUDY OF THE PHYSIOLOGY OF BACTERIA 



broth is rendered cloudy or remains clear, and whether there 

 is a deposit at the bottom or not (Fig. 142). An abundant 

 surface growth with little or nothing below indicates a strict 

 aerobe, while a growth or deposit at bottom and a clear or 

 nearly clear medium above an anaerobe. These appear- 



'^1 



Fig. 14.3.— a fili- 

 form stab or punc- 

 ture culture. X f . 



Fig. 144.— .A. beaded 

 stab or puncture cul- 

 ture. X i. 



Fig. 14.5.— a vill- 

 ous stab or puncture 

 culture. X j. 



ances are for the first few days only of growth. If the broth 

 is disturbed, or after the culture stands for several days 

 many surface growths tend to sink to the bottom. So an 

 actively motile organism causes in general a cloudiness, 

 especially if the organism is a facultative anaerobe, which 

 tends to clear up by precipitation after several days when 



