84 PHYSIOLOGICAL ACTIVITIES 



bacteria which produce disease, though even here some CH4 

 is present. The common Bacillus coli forms all three, though 

 the CH4 is in smallest quantity. 



In the fermentation of the polysaccharids — 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 five feet long and six inches in 

 diameter, 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 lbs. were attached (Fig. 59). 

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

 the limits of the readings on it. IMost 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 analysis by 

 Prof. D. J. Demorest of the Department of jNIetallurgy : 



CO2 . . . .18.6 per cent. 



CH4 ... . 76.1 



H . 1.0 " 



N ... . . . 4.3 " 



In the author's opinion natural gas and petroleum have 

 been formed in this way^ (Pigs. 60 and 61). 



One of the very few practical uses of the gaseous fermen- 

 tation of carbohydrates is in making "salt rising" bread. 

 The "rising" of the material is due not to yeasts but to the 

 formation of gas by certain bacteria which are present on 

 the corn meal or flour used in the process (Fig. 62). 



1 See "Oil and Gas in Ohio," Bo wuocker : Geological Survey of Ohio, Fourth 

 Series, Bull. I, pp. 313-314. 



