192 



through the little "stem" into the larger 

 stem. The large stem serves as a tube or 

 duct which carries the juice into some 

 part of the alimentary canal. Examples 

 of this type of gland organ are the three 

 pairs of salivary (saPi-very) glands, the 

 pancreas (pan'cree-as), and the liver. 

 Locate these organs on the diagram of 

 the digestive system, page 189. 



The salivary glands empty their juice, 

 saliva, into the mouth. Some of the glands 

 open into the inside of the cheek; others 

 open under the tongue. The pancreas 

 lies behind the stomach, more or less 

 crosswise in the abdominal cavity. Its 

 juice, the pancreatic juice, enters the 

 small intestine close to the opening from 

 the stomach. The liver is by far the 

 largest gland of all; it lies above the 



Houo a Complex Animal Uses Food unit iv 



you can feel a smooth, moist membrane. 

 This delicate lining membrane is called 

 nnicous (mew'kus) membrane. It lines 

 not only the mouth but the whole alimen- 

 tary canal from beginning to end. The 

 membrane secretes a slimy, thickish sub- 

 stance called imicus. It is the mucus 

 which keeps the membrane smooth and 

 helps the easy passage of food. 



Now provide yourself with a mirror 

 and some food. You can learn at first 

 hand how the mouth deals with food. 

 You can discover what the tongue does 

 in chewing and swallowing and in tast- 

 ing by doing Exercise 6. It will be worth 

 while also to make a study of the teeth 

 as suggested in Exercises 7, 8, 9, and 10. 

 The food an animal eats is often partially 

 determined by the kind of teeth it has. 

 stomach mostly on the right side. Under See Figure 203. Chewing is a purely me- 



it and connected with it is a little storage 

 sac known as the gall bladder. 



As the liver continues to secrete, the 

 juice known as gall or bile leaves the 

 liver and accumulates in the gall bladder. 

 After digestion is well under way the 

 gall bladder, which has thin muscular 

 walls, contracts slightly and releases the 

 bile. The juice flows along a duct which 

 joins the duct from the pancreas and 

 thus it reaches the alimentary canal. 

 While the liver, pancreas, and salivary 

 glands are not part of the alimentary 

 canal through which the food is pushed, 

 they are just as necessary to the whole 

 process of digestion as the canal itself. 

 This would be a good time for you to 

 dissect a frog to see the internal organs 

 in a freshly killed animal. See Exercises 

 4 and 5. 



Food in the mouth. If you explore the 

 inside of your mouth with your fingers 



chanical preparation of food for diges- 

 tion. Chewing breaks up food and mixes 

 it with saliva. Digestion begins when 

 saliva touches the food. Normally the 

 food remains in the mouth for so short 

 a time that not much of the starch can be 

 digested before the food is pushed on 

 toward the stomach. You can learn by 

 the simple experiment outlined in Exer- 

 cise 1 1 how long it takes for starch to be 

 changed into sugar in the mouth. 



As soon as you begin to eat, juice flows 

 from the salivary glands very freely. The 

 presence of food in the mouth starts the 

 glands secreting actively. But the smell 

 and thought of food also is enough to 

 start their increased activity. Surely you 

 have seen a hungry^ dog watching the 

 preparation of its food. Why does it lick 

 its lips? 



Food leaves the mouth. Although you 

 usually do not think about swallowing. 



