202 ^ How a Co?nplex Animal Uses Food unit iv 



3. Do active plant cells digest starch? The cells of a dried grain of corn 

 are living but quite inactive. They will become active when the grain 

 is soaked; it will then sprout. Soak grains for 24 hours. Keep them moist. 

 After 4 or 5 days test dry and sprouted grains for sugar and starch. What 

 do you notice? Be sure to keep accurate notes. How can you explain what 

 happens? Did you use a control? What was it? 



4. Ho'iv to dissect a frog. Lay a dead frog in a shallow pan with ventral 

 (lower) side up. With your forceps grasp the loose body wall in the ex- 

 treme lower part of the body cavity where the legs arise. Cut into this 

 body wall with the point of your scissors making a large enough incision 

 for you to introduce the point of one blade. Now remove the body wall, 

 cutting out a complete rectangle. Caution: As you cut, the scissors must 

 be held horizontally and with the forceps you must raise the body wall in 

 front of the scissors. In this way you will not damage the organs within. 

 Cut from the point of incision to your right (the frog's left) across the 

 lower portion, then up along the side until you reach the head. In the 

 region of the arms you will be obliged to cut through the bones which 

 make the shoulder girdle. Then cut the third side of the rectangle and 

 back along the left (the frog's right) side. When you have removed this 

 large piece of body wall the internal organs of the frog will be exposed. 



5. Study of the internal organs. During the breeding season the female 

 frog will have large masses of eggs. These must be removed before you 

 can see the other organs. The heart may attract your attention since it 

 may be beating. In the region of the heart toward the front end of the 

 body cavity are the large, flat, dark red lobes of the liver. How many are 

 there? Attached to the liver you will find the gall bladder which is green. 

 What is its shape? Partly under the liver on the frog's left side is the 

 long, whitish tubular stomach. Feel it with the dull point of the forceps. 

 How does it feel? At its lower end it narrows to form the tubular intes- 

 tine. Trace the coils of the intestine. You will find that it is held down 

 and held in place by a very thin membrane called the mesentery. Do you 

 see fine blood vessels in the mesentery leading to the intestinal wall? The 

 small intestine widens into the large intestine. Caught in the folds of the 

 mesentery in the region of the stomach is the long narrow pancreas. 



Other organs you will see are: the spleen, a dark red ball; lying against 

 the back wall in the region of the heart, two narrow pointed pinkish 

 lavender bags, the lungs; against the back wall two dark red, rectangular 

 organs close together, the kidneys; close to the kidneys, perhaps, a pair of 

 yellow organs if you are studying a male frog, the male reproductive 

 organs. Try to inflate the lungs by inserting a tube through the frog's 

 mouth and blowing into it. 



6. Study your tongue with a hand mirror. Where and how is your 

 tongue attached? Which parts of your mouth can be touched by your 

 tongue? When would these movements of the tongue be of help to you? 

 Explain. Put a drop of sugar water on the front of your tongue; on the 



