6o « SULPHUR BACTERIA 



A small conical flask (50—100 c.c.) containing a depth of 

 I — 1-| cms. of this solution was infected with sulphur bacteria, 

 and exposed to an atmosphere of sulphuretted hydrogen. 

 In 10 — 30 days a vigorous development of bacteria took 

 place, and a rich red-purple zoogloea covered the chalk 

 sediment. 



Source of Nitrogen. — The most satisfactory of the nitro- 

 genous compounds experimentally added was found to be 

 ammonium sulphate, only slightly less satisfactory album.en, 

 peptone, and asparagin. As already stated these organic 

 compounds are not regarded by Skene as being directly assimi- 

 lated. The most suitable concentration of ammonium sulphate 

 was found to be O-i per cent. 



Sources of Carbon. — Using ammonium sulphate as the 

 source of nitrogen he next determined the source of carbon. A 

 large number of organic substances were put under requisition, 

 but Macgregor Skene came to the conclusion that not one of 

 them was assimilated by the sulphur bacteria. Since vigorous 

 growth occurred in the second and third generations in the 

 mineral solution given above, he concluded that the carbon 

 constituents necessary for the building up of bacterial cells 

 could not have been contained in the original infecting material, 

 and such being the case the carbon could have no origin other 

 than the carbon dioxide of the atmosphere. Without pure 

 cultures he was not able to confirm this statement. A series 

 of experiments is recorded by this investigator to determine 

 w^hether the sulphur bacteria obtained COg from the atmosphere 

 directly or through the medium of an autotrophic bacillus 

 which constantly appeared in his cultures and which was easily 

 isolated. 



Eight flasks were infected with a pure culture of the bacillus 

 and set aside for twelve days. Four were then sterilized, and 

 to the collection four uninoculated flasks were added. Of 

 the twelve flasks three from each series were infected with 

 purple sulphur bacteria, so that the following experimental 

 conditions could be obtained : — 



