FERMENTATION OF CARBOHYDRATES 79 



duced are carbon dioxide (CO2) and hydrogen and marsh gas 

 (CH4). Other gases of the paraffin series may also be formed 

 as ethane (C2H6), acetylene (C2H2), etc. CO2 and H are the 

 ones usually formed from sugars by the few gas-forming 

 bacteria which produce disease, though even here some CH4 

 is present. The common Escherichia coll forms all three, 

 though the CH4 is in smallest quantity. 



In the fermentation of the poly saccharids— starch and 

 especially cellulose and woody material— large amounts of 

 CH4 occur, particularly when the changes are due to anae- 

 robic bacteria. This phenomenon may be readily observed 

 in sluggish streams, ponds and swamps where vegetable 

 matter accumulates on the bottom. The bubbles of gas 

 which arise when the mass is disturbed explode if a lighted 

 match is applied to them. 



The author has conducted a number of experiments to 

 demonstrate this action as follows: Material taken from the 

 bottom of a pond in the fall after vegetation had died out 

 was packed into a cylinder 5 feet long and 6 inches in 

 diameter and water was added to within about 2 inches of the 

 top. After leaving them open for a few days to permit all 

 the dissolved oxygen to be used up by the aerobes, the cylin- 

 ders were tightly capped and allowed to stand undisturbed. 

 Pressure gauges reading to 500 pounds were attached (Fig. 53). 

 At the end of six months the gauge showed a pressure beyond 

 the limits of the readings on it. Most of the gas was col- 

 lected and measured 146 liters. An analysis of portions 

 collected when about one-half had been allowed to escape 

 showed the following composition, according to Prof. D. J. 

 Demorest, of the Department of Metallurgy: 



CO2 18.6 per cent. 



CH4 76.1 



H 1.0 " 



N 4.3 



Another experiment with a cyhnder tested to withstand 5000 pounds per 

 square inch is now under way. The pressure in February, 1929, had reached 

 750 pounds. 



"new substances are formed which are not constituents of the original mole- 

 cule." It may be doubted whether this restriction is justified or necessary. 

 A definition is at present scarcely possible except when the qualifying adjec- 

 tive is included as "alcoholic fermentation," "ammoniacal fermentation." 

 "lactic acid fermentation," etc. 



