50 PHYSIOLOGY OF FARM ANIMALS [CH. 



protein is absorbed by the gut in the form of amino-acids; and 

 as b}" improved technique it has been shown that amino-acids 

 are normally present in the blood, thert> is little reason still to 

 believe that these amino-acids are re-synthesised into protein 

 within the walls of the intestine. Water and salts are absorbed 

 and taken up by the blood vessels with great rapidity. 



The inlet and outlet to the small intestine are regulated by 

 sphincters. The total length of the small intestine in the horse 

 is aboiit 70 feet ; that of the ox is 130 feet, but the diameter is 

 very much smaller. The small intestine in the sheeji is 80 feet 

 and in the jDig 60 feet. It has been found that in the horse 

 water takes from five to fifteen minutes to traverse the length of 

 the small intestine ; semi-digested food takes a much longer time. 



The Large Intestines. 



The large intestines comprise the colon, the coecimi, and 

 the rectum. Each of these parts is composed of the same four 

 coats as the small intestine. Lieberkiihn's crypts are repre- 

 sented, but there are no Bi miner's glands and no villi (excepting 

 in the coecum in the horse and some other animals) neither are 

 Payer's patches to be found. In man and some animals an ileo- 

 coecal valve at the entrance to the large intestine prevents 

 a reflux into the small intestine. It is made up of two semi- 

 lunar folds of the mucous membrane. 



The coecum varies in importance according to the character 

 of the food. In man it is a short wide pouch ending with the 

 small appendix vermiformis which is largely composed of 

 lymphoid tissue ; it is this structure which is frequently removed 

 surgically as a consequence of the inflammatory condition or 

 infection known as appendicitis. In the carnivora the coecum 

 is likewise vestigial or absent. In all herbivora on the other 

 hand it is large and functional. 



In the horse the capacity of the coecum is enormous, being 

 about 8 gallons (while its length is 4 feet). It acts as a reservoir for 

 intestinal digestion. Everything must traverse it in passing from 

 the ileum to the colon. The two openings are placed near to- 

 gether, and the outlet is above the inlet, so that the substances it 

 contains have to pass out against gravity in order to enter the 

 colon. The contents of the coecum are always fluid and some- 

 times watery; their reaction is alkaline. Its main function is 



