THE ANIMAL BODY DIGESTION METABOLISM 25 



from various poisonous substances, either taken accidentally in the food 

 or formed in the digestive tract thru putrefaction, doing this by uniting 

 these substances with others to form compounds which are not poisonous. 



Bile is *a greenish or golden colored fluid, alkaline and extremely 

 bitter in taste. In cattle, sheep, and swine the bile, as secreted, is stored 

 in the gall bladder, whence it is poured thru a duct into the intestine. 

 The horse has no gall bladder, the bile passing directly into the intestine 

 as it is secreted. Bile contains no enzymes, but is nevertheless exceedingly 

 important in digestion, as it furnishes the alkalies necessary to change 

 the fatty acids formed by lipase into soaps, in which form they may be 

 absorbed. It also aids in emulsifying the undigested fat ; i. e., breaking 

 it up into very minute droplets, so it will present a large surface and 

 be more readily and rapidly acted on by the lipase. Moreover, it dis- 

 solves the fatty acids and soaps, so that they are more readily absorbed 

 by the small intestine. After performing these important functions, 

 the bile is not wholly excreted with the contents of the intestine, but 

 is in part taken up by the circulation and utilized again. According 

 to Colin, the liver of the horse secretes over 13 Ibs. of bile during each 

 24 hours, of the ox 5.7 Ibs., and of the sheep 0.75 Ib. 



In addition to its action on fats, bile stimulates the action of the 

 pancreatic juice, checks putrefaction, and also aids in the passage of 

 food thru the intestines by increasing the muscular contractions of the 

 walls. Furthermore, in the bile there are excreted waste products which 

 would be harmful if retained in the body. 



44. The intestinal secretion. The digestive fluid secreted by the mucous 

 membrane of the small intestine contains several enzymes, the most 

 important of which are erepsin and the invertases. 



Erepsin, an enzyme of great digestive power, attacks the proteoses and 

 peptones which have escaped the action of trypsin and breaks them up 

 into amino acids. It can not act on protein which has not already been 

 split into proteoses and peptones. 



The invertases (sucrase, maltase, and lactase) change cane sugar, malt 

 sugar, and milk sugar into the simpler glucose-like sugars. 



Due to the vigorous action of the pancreatic juice, the bile, and the 

 intestinal secretion, digestion is very thoro in the small intestine and 

 under ordinary conditions little that is useful escapes digestion. Most 

 of the digested matter is absorbed from the small intestine, thus entering 

 the body proper, as is shown later in this chapter. 



45. The large intestine. From the small intestine the undigested 

 matter passes into the large intestine. Little, if any, digestive fluid is 

 produced here, but a small amount of digestion may go on, owing to the 

 digestive enzymes carried in from the small intestine and to the action 

 of bacteria. From the large intestine are absorbed any soluble products, 

 nutritive or otherwise. The bacteria may not only attack cellulose in the 

 large intestine but also may cause the putrefaction of undigested protein, 

 in which action foul-smelling substances are formed that are poisonous if 



