The Animal Body — Digestion — Metabolism. 23 



ter. The small intestine first receives digestive fluids from two out- 

 side organs, the liver and the pancreas, whose functions in nutri- 

 tion are of the highest importance, while farther on the food is 

 mixed with a secretion containing several enzymes which are pro- 

 duced by the intestine itself. Immediately on entering the small 

 intestine the inpouring material is changed from an acid to an alka- 

 line character thru rapid addition of the bile and pancreatic juice, 

 both alkaline. 



34. The pancreas. — The pancreas is a slender gland lying just be- 

 yond the stomach and connected with the small intestine by a duct. 

 Its secretion, the pancreatic juice, varies in different animals, being 

 thin, clear, and watery in some, and thick, viscous, and slimy in 

 others. The pancreatic juice bears three enzymes— trypsin, amy- 

 lopsin, and steapsin. 



Trypsin is an enzyme which, like pepsin, converts protein into 

 proteoses and peptones. It has the power of further cleaving these 

 two partially digested substances into amino acids, which constitute 

 the ultimate useful nutrients which come from the cleavage of all 

 the proteins of food stuffs thru digestion. The digestion of protein 

 goes on much more thoroly in the small intestine under the influ- 

 ence of trypsin than it does in the stomach with pepsin. 



Amylopsin is a pancreatic enzyme which converts starch into 

 glucose-like sugars. 



Steapsin is a pancreatic enzyme which splits fats into fatty acids 

 and glycerin. 



Ordinarily, when digestion is not going on there is no secretion 

 by the pancreas. It has been found that if the mucous lining of 

 the first part of the small intestine is treated with dilute hydro- 

 chloric acid, the pancreas at once pours out its secretion. It will 

 be remembered that the contents of the stomach, at the time of 

 their ejection from that organ into the small intestine, are strongly 

 acid because of the hydrochloric acid of the gastric juice. This 

 acid when it pours into the small intestine, acting on the lining of 

 the latter, produces something which, when absorbed into the 

 blood, calls forth the pancreatic secretion just when needed — a 

 forceful illustration of how all the organs of the complicated di- 

 gestive tract work in harmony. 



35. The liver. — The liver, the largest organ in the body, has nu- 

 merous duties in the digestion and metabolism of nutrients. While 

 some of its functions will be dealt with in a later chapter, attention 



