100 PRINCIPLES OP VETERINARY SCIENCE 



the form in which all carbohydrates must be converted for 

 absorption; enterokinase, which converts trypsinogen into trypsin. 

 Another important constituent is carbonate of soda, which 

 neutralizes further the acid chyme thereby preparing it for 

 absorption. 



(D) Digestion in the Large Intestine. — From the small intes- 

 tine the ingesta pass into the cecum, where they may remain 

 from twenty-four to thirty-six hours in most animals. The 

 cecum is undoubtedly a most important digestive organ in the 

 horse because of its large size and the length of time food remains 

 in it. It always contains considerable ingesta mixed with much 

 water. Ellenberger has called the cecum the second stomach, 

 in which maceration, fermentation, and decomposition changes 

 occur in the food to fit it for absorption. 



The chief constituent of the roughage in horse feed is cellulose. 

 Cellulose forms the skeleton of plants, and is present as undi- 

 gested particles in the contents of the cecum and colon. On 

 account of its resistant character, it escapes digestion both in 

 the stomach and small intestine of the horse. In the large 

 intestine, however, its .destruction is brought about by the 

 myriads of bacteria which thrive in the warm, moist, anaerobic 

 conditions that there prevail. 1 In ruminants this process 

 takes place largely in the stomach. 



Most of the microorganisms that act on cellulose are anae- 

 robic. They break down the resistant vegetable cells and the 

 cellulose disappears. Just what, if any, part is played by the 

 digestive enzymes in cellulose digestion is a mooted question. 



1 Cellulose destruction by bacteria can be well demonstrated by placing 

 strips of filter-paper in a solution composed of 



Dibasic potassium phosphate 1.0 gram. 



Magnesium sulphate 0.5 gram. 



Ammonium sulphate 1.0 gram. 



Calcium carbonate 5.0 grams. 



Water 1000. grams. 



A large test-tube should be filled two-thirds with this solution, and 2 

 grams of horse feces together with two strips of filter-paper added. To 

 exclude air and closely approximate conditions found in the intestines a 

 layer of paraffin oil J.<j inch deep must be poured over the surface of the mix- 

 ture. Then incubate the tube at 37°C, until signs of decomposition appear 

 and test for starch, sugar, carbon monoxide, carbon dioxide, free hydrogen, 

 and marsh gas. 



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