CHAPTER IV. 



THE CULTURE OF THE SULPHUR BACTERIA. 



Methods of Culture. 



General Considerations. — It is desirable to cultivate the 

 sulphur bacteria in a medium which does not contain any 

 other microorganisms : and this is particularly the case in the 

 investigations of physiological problems. If other organisms 

 are present it becomes very difficult, and sometimes impossible, 

 to estimate the exact contribution of the sulphur bacteria 

 to the production of any particular phenomenon which may 

 be under investigation. At the same time it is also advan- 

 tageous to study the sulphur bacteria in a mixed field, for a 

 truer presentment of their normal state is thereby given : 

 it is very seldom that bacteria grow and multiply in nature 

 uninfluenced by other organisms. The best conditions for the 

 morphological study of these, as well as of other bacteria, 

 obtain when the organism under investigation is present in 

 its natural habitat, and is easily recognizable. Under artificial 

 conditions, as for example in pure cultures, they are apt to 

 depart from the normal, both in their habits and in their life 

 histories. We must therefore accept with caution the dis- 

 counting of certain positive results obtained from the study of 

 the organisms under one set of conditions, on the strength of 

 negative results obtained from their investigation under totally 

 different conditions. 



Winogradsky's Methods. — To Winogradsky must be given 

 the credit for the pioneer work on methods of culture. 



{a) Rhizomes of Water-plants {Butomiis, etc.) with adhering 

 mud were placed in a deep vessel, and water and gypsum added. 

 The vessel, covered with a glass plate, was then placed in a 



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