154 



ATLAS OF BACTERIOLOGY. 



always, even when the nutrient medium is free from 

 cellulose, forms some marsh gas in addition to car- 

 bonic acid and hydrogen. 



In order to determine whether gas is formed, we 

 should use the agitation culture on one-per-cent grape 



FIG. 11. Bacterium Coli upon Sugar Agar at the end of Twelve, Twenty- 

 four, and Forty-eight Hours. 



sugar agar. At the end of twenty-four hours (often 

 at the end of eight to twelve hours when incubating 

 temperature may be employed) the agar is infiltrated 

 with bubbles of gas or even split up by numerous 

 deep rifts and fissures. If the gas is to bo measured 

 or analyzed, it is best, according to Th. Smith, to re- 

 ceive it in the fermentation flask which has been used 



