SUGAR IN THE NUTRIENT MEDIUM. 153 



may mention the splitting up of cellulose by various 

 bacteria, which are found particularly in the gastric 

 and intestinal contents of herbivora, and in muck, 

 and which form marsh gas as a striking product. 



Unfortunately the decomposition of cellulose by 

 bacteria has been imperfectly studied. It appears to 

 be certain, however, that at least one anaerobic variety 

 decomposes cellulose into marsh gas and carbonic 

 acid. But the most recent investigator of this ques- 

 tion, Van Semis, maintains that the anaerobic bacil- 

 lus amylobacter isolated by him will attack cellulose 

 only in symbiosis with another small bacillus (vide 

 the resume by Herzfeld: C. B., Part L, Vol. II., p. 

 114). 



13. Formation of Gas from Carbohydrates and other 

 Fermentible Fatty Bodies. 



The only gas which develops in visible amounts 

 upon a non-saccharine nutrient medium is nitrogen. 

 If sugar is vigorously attacked by bacteria, the devel- 

 opment of gas may be lacking inasmuch as pure lactic 

 or acetic acid is produced (for example, typhus 

 bacillus on grape sugar) ; but very often there is a 

 notable development of gas, especially when the air 

 is excluded. About one-third of the varieties which 

 form acid vigorously also produce an abundance of 

 gas. This consists of carbonic acid which, accord- 

 ing to Smith (C. B., XYIII., 1) is always combined 

 with hydrogen. Marsh gas appears to be formed 

 rarely (apart from the bacteria which decompose cel- 

 lulose). Last year Mr. Conrad isolated in my labor- 

 atory, a bacterium allied to bacterium coli, which 

 gives rise to the fermentation of sauerkraut and 



