102 PRINCIPLES OF VETERINARY SCIENCE 



being more plentiful when grass and other succulent feed com- 

 prise a large part of the ration, than when dry feeds are consumed. 

 Cattle eliminate about 56 per cent, of the water drunk in the 

 feces. The organic matter consists of waste products of glandular 

 secretions such as bile pigments, cholesterin, and mucus; great 

 numbers of bacteria; the woody parts of the roughage; proteins 

 that escape digestion, and the residue from protein metabolism. 

 The inorganic salts of sodium, calcium, potassium, magnesium, 

 and iron are found in different amounts. Both sodium and 

 potassium are in comparatively insoluble forms. 



A thin coating of mucus covers the feces and gives them a shiny 

 appearance. Smith observed that horses on a diet consisting 

 of 12 pounds of hay, 6 pounds of oats, and 3 pounds of bran 

 passed 29 pounds 13 ounces of feces in twenty-four hours. It 

 takes about four days for food to pass through the alimentary 

 tract of the horse, but solid bodies have been found in the feces 

 after twenty-four hours. 



Meconium is the fecal material found in the intestines of the 

 fetus. It consists largely of waste products from the liver. The 

 first milk (colostrum) contains substances which hasten bowel 

 action and cause the meconium to be expelled soon after birth. 



The essential points mentioned in connection with digestion 

 may be summarized as follows: Digestion involves a reduction 

 of foods to relatively simple, water-soluble forms. Most of the 

 carbohydrates are changed to sugars by the action of starch- 

 splitting enzymes, the fats to fatty acids and glycerin, and the 

 proteins to amino-acids. 



THE PHYSIOLOGY OF ABSORPTION 



Absorption is the process of taking up the materials in solution 

 which have been prepared and modified by the secretions during 

 digestion. 



The cells of the intestinal wall are the active agents that select 

 prepared nutrients from the ingesta, while the blood and lymph 

 act as transporters of these substances to all parts of the body. 

 The process of absorption resembles secretion in that it is not a 

 simple diffusion or osmosis of fluids operating under physical 

 forces, but is due to the selective action of the living epithelial 

 cells which cover the intestinal villi. It differs from secretion 

 in that fluids are taken up instead of being poured out. To 



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