THE DIGESTIVE SYSTEM 101 



It seems doubtful whether they exert any action, for when cellu- 

 lose is broken down not the slightest trace of sugar can be found, 

 but large amounts of carbon are liberated. It is thought that the 

 carbon combines with hydrogen to form methane, and with 

 oxygen to form carbon dioxid. The expired air contains these 

 gases in relatively large quantities, which has led physiologists 

 to think that, in the horse at least, we can account for their pres- 

 ence in large measure by cellulose destruction. There is reason 

 to believe that the more resistant cellulose-containing portions 

 of the food are not transformed until they have been acted upon 

 by the various agents noted above and reach the last portion of 

 the large colon. On the strength of these facts, it seems unrea- 

 sonable to attribute much energy value to cellulose destruction. 

 The process may be considered simply an accident in the course 

 of digestion. 



Some of the aerobic microorganisms found in the bowels have 

 a lipolytic action, i.e., the power of splitting fat. So have the 

 juices of certain molds. The seeds of certain plants high in oil 

 also contain a lipase that is liberated on germination and when 

 their capsules are destroyed in the course of the digestive process. 



Armsby says that the horse is unable to digest more than 30 

 per cent, of the combustible materials in roughage. Ruminants 

 are more economical feeders, digesting about 40 per cent. In the 

 case of concentrates about 80 per cent, are digested by ruminants 

 and 60 per cent, by the horse. 



Immediately after passing into the small colon a very marked 

 change occurs in the character of the intestinal contents; from 

 a greenish-brown pea-soup-like fluid it becomes firmer and resem- 

 bles quite closely fresh feces. As the material is moved on 

 toward the rectum it gets drier and is molded into characteristic 

 forms through the action of the muscular bands in the walls of the 

 small colon. Smith states that the reaction is still alkaline or 

 neutral at this point, but after reaching the rectum a distinctly 

 acid reaction is noted on the surface of the feces. 



Feces represent the residue of digestion. In the horse they 

 have a characteristic earthy odor due to indol, skatol, and hydro- 

 gen sulphide. When digestive disturbances are present they 

 become extremely offensive. Fresh horse feces contain about 

 74 per cent, water, 23 per cent, organic matter, and 3 per cent, 

 inorganic matter. The water varies with the character of the feed, 



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