84 AGRICULTURAL BACTERIOLOGY 



carbon-dioxide therein. This is dissolved in the soil water, 

 thereby increasing materially its solvent effect on certain 

 of the minerals of the soil. 



Organic acids are always produced in the decomposition 

 of carbohydrates. In poorly aerated soils these tend to 

 accumulate, forming the raw or acid humus noted in marshy 

 soils. Hydrogen and also methane may be formed. The 

 latter is commonly called marsh-gas, from its formation in 

 water-logged areas by anaerobic and facultative bacteria. 



Cellulose decomposition. The decomposition of certain 

 carbohydrates is of special importance to the farmer. The 

 great mass of plant tissue consists largely of cellulose, a com- 

 pound that is insoluble in water and resistant to decompo- 

 sition. The plant fibers, such as cotton and hemp which are 

 used for industrial purposes, consist of cellulose. The 

 larger portion of organic matter in barnyard manure also 

 consists of cellulose. It is believed that cellulose is acted 

 on by microorganisms with the formation of sugars, as in 

 the case of starch. In the soil these are at once changed to 

 still simpler compounds. 



Quantities of cellulose are contained in the rough feed, 

 hay and grass, consumed by animals. It has been found 

 that ruminants can digest about 75 per cent, of the cellulose 

 contained in the feed; horses about 50 per cent., man about 

 25 per cent, of that contained in young, tender plants, while 

 the dog can not digest cellulose at all. As has been previ- 

 ously stated, all insoluble foods ingested by the animal are 

 supposed to be changed to soluble compounds by the action 

 of enzymes elaborated by the animal body. No enzyme 

 capable of acting in cellulose has, as yet, been demonstrated 

 in the animal body. The only explanation that can be 

 offered is that bacteria, which change the cellulose to sugars, 

 are present in the alimentary tracts of animals and that 

 these sugars are utilized by the animal. 



