1 88 EQUI>J£ PHYSIOLOGY. 



The Colon acts principally as an absorbing area, the food pass- 

 ing through its several curvatures and the floating colon before 

 reaching the rectum. The diaphragmatic curvature contains 

 large amounts of fluid. 



THE F^CES. 



The residue of aliment after digestion is expelled from the 

 rectum in rounded balls as faeces. Horses defecate every three 

 hours, and will pass about 17 kilos or 37.4 pounds, or 5.8 of 

 solids. 



About 13 per cent, are inorganic materials. 



DEFECATION. 



Defecation is the process of evacuation of the rectum. The 

 presence of fecal matter in the rectum leads to the desire to 

 expel it. The brain then sends an inhibitory action to the reflex 

 centre in the lumbar cord, which causes a relaxation of the 

 sphincter muscles. Contraction of the abdominal muscles and 

 small colon, with the circular fibres of the rectum, then take 

 place, causing a propulsion of the faeces through the anus. The 

 mucous membrane of the opening is everted, then pulled back 

 by the retractor muscles. 



INTESTINAL MOVEMENTS. 



The food is carried along by peristalsis, a worm-like motion of 

 the intestine due to involuntary contraction of both the longitudi- 

 nal and circular muscular fibres. The irritation of the bile is an 

 active factor in keeping it up. 



ABSORPTION. 



Absorption is the process of taking up the food principles after 

 digestion, also water and salts that have not been acted upon. 

 It takes place by means of lymphatics and veins. 



By veins. — The water, salts, sugar, soaps and peptones are ab- 

 sorbed quickly by osmosis, and also by some special function of 

 the epithelial cells of the villi. 



By lymphatics. — This takes place by the villi (see bitestines) ; 

 the emulsified food elements passing into their interior by the 

 interr,e'lular connective tissue, then by the lymph channels of the 



