428 Animal Biology 



ileum which widens into the large intestine. The latter connects with 

 the saclike cloaca. The latter also receives tubes from the kidneys and 

 reproductive system. The cloaca empties to the exterior through the 

 anus which is located between the two hindlegs. 



The pancreas is a much-branched, tubular organ which lies between 

 the stomach and the duodenum. It passes its alkaline digestive juices 

 into the common bile duct (Fig. 213). The large, reddish, trilobed liver 

 secretes an alkaline bile which is carried to the gall bladder from which 

 it enters the duodenum together with the pancreatic juices through the 

 common bile duct. 



The Physiology of Digestion: Digestion breaks down complex, insolu- 

 ble foods, such as proteins, fats, and carbohydrates, into simple, soluble 

 compounds capable of being absorbed by the cells and assimilated into 

 living protoplasm. The foods in the cells are constantly being used and 

 must be replaced in order to supply energy and chemical substances to 

 carry on the various life activities. 



Uses of Foods in the Body of the Frog 



The various foods are acted upon by specific enzymes (ferments) which 

 hasten the above conversion processes without being used up themselves. 

 Because enzymes are so important, it may be well to list briefly some of 

 their more important characteristics. Enzymes are manufactured by liv- 

 ing protoplasm from foods and other materials which are brought to it. 

 Enzymes are specific for certain substances. For example, the enzyme 

 pepsin acts only on proteins and not on carbohydrates or fats. Enzymes 

 have an optimum temperature at which they can act most efficiently. A 

 temperature of 100° C. usually destroys the action of enzymes, while at 

 0° C. they are usually rendered very inactive. They also usually react 



