WHAT FOOD MATERIALS ARE PRESENT

IN PLANTS? (XXVIII-1)

The problem. Plants provide food material not only for themselves but directly or indirectly for all other living things. It should prove interesting to determine what are some of the food materials to be located in some common plant substances.

What to use. Potato, rice, products of wheat, oats, or corn, test tube, Bunsen burner, test-tube stand, test-tube brush, iodine solution, test-tube holder, Fehling's solutions A and B, glucose (corn sirup), ordinary sugar, nitric acid, ammonia, teaspoon.

What to do. 1. Starch. Test the food sample for starch as follows: Crush some ordinary starch and boil it in a test tube. It is best to warm the tube slowly and uniformly at first. If the bottom of the test tube is heated too long at one time the glass may break or the water may suddenly boil over the top of the tube. When the solution cools add a drop or two of tincture of iodine solution. If a small amount of the solution is added a blue color will appear. If an excess is added the color will be black. Use this method in treating other foods.

2. Glucose. Test the food sample for glucose as follows: Pour into a test tube equal amounts (5 cc.) of Fehling's solutions A and B. Mix the solutions until a deep blue color is obtained. Heat this mixture almost to boiling and add a few drops of glucose (corn sirup). The red or yellow color shows the presence of glucose.

3. Cane sugar. Repeat the test given in 2, using some granulated cane sugar. Pure sugar will not produce the color changes observed in 2.

4. Protein. Crush the material and boil it in water. Add a few drops of concentrated nitric acid. Caution: If nitric acid comes in contact with the hands a rather permanent yellow color is

produced. A yellow color indicates protein. This color changes to orange by the addition of ammonia. Since plant proteins are not soluble the color will appear on the fragments.

5. Fats and oils. Put small pieces of the material, such as cheese or corn meal, on unsized paper and hold it above the flame so as to avoid charring the paper. A grease spot indicates fat.

6. Mineral matter. Place the sample in a teaspoon and heat in a draft until no more fumes are given off. Next burn off the carbon. The white ash remaining consists of compounds of various metals present in the food.

Questions. Is the iodine starch test a delicate test? Describe the changes in color produced by the glucose. Can the above kinds of foods be distinguished from one another by superficial observations?

Suggestions for report. Enter the results in the table below:

MATERIAL STARCH GLUCOSE

CANE
SUGAR

PROTEIN

FAT

MINERAL
MATTER

Reference work. Read sections 330 to 333.

Optional problems. Extend this work by testing other avail

able plant foods.

CAN STARCH BE DIGESTED OUTSIDE THE BODY
OF A PLANT OR AN ANIMAL? (XXVIII-2)

The problem. Solid foods cannot be used for nourishment as solids. Plants and animals have many processes and methods of transforming foods so as to make them available for replenishing wasted tissues, for building new ones, or for providing energy for work. How is a solid food, like starch, changed into a soluble form?

What to use. Test tubes, starch paste, malted barley or barley grains, iodine solution, Fehling's solutions, mortar, filter paper, and funnel.

What to do. 1. Partly fill a large test tube or a cup with starch paste made by boiling a half teaspoonful of starch in a half pint of water.

2. Prepare a malt extract by grinding dry malted barley in a mortar or a coffee grinder, soaking one or two tablespoonfuls of the barley in a cupful of water for an hour, and filtering off the water, which with the substances in solution is the malt extract. If malted barley cannot be had, soak some fresh barley grains in water for from ten to twelve hours, pour off the water, and place the barley in a closely covered dish in a warm place to germinate. When the sprouts are an eighth of an inch long, crush the barley, soak in water, and treat as above.

3. To a test tube of starch paste add one or two cubic centimeters of the malt extract. Allow the mixture to stand for at least half an hour, preferably in a warm place. It may stand overnight with advantage. Test a small sample for.starch. Test another sample for grape sugar.

Questions. What change has taken place as to the amount of starch present? of grape sugar? How do you account for these changes?

Suggestions for report. Write a brief summary of the facts shown by this experiment.

Reference work. Read sections 334 to 340.

Optional problems. Put some powdered starch in cold water in a test tube, add a small amount of malt extract and leave in a warm place for twenty-four hours or more. Test with Fehling's solutions to see if sugar is present. If a microscope is available, examine starch grains which have been acted upon by the malt extract and compare them with starch grains which have not been treated with malt. Do any of the grains show evidence that they have been partly digested?

TRANSPORTATION OF DIGESTED FOOD IN ANIMALS

(XXIX-1)

The problem. The blood serves as a carrying medium for taking materials to and from the tissues of the body. It is the indispensable transportation system in the human body, and it is worth while to know something about its nature.

What to use. Compound microscope, microscope slide and cover glass, vaseline, needle, and alcohol.

What to do. 1. This experiment should be prepared as a class demonstration. Sterilize a sharp needle by holding it in a flame for a few minutes. Wash the ball of the middle finger of the left hand with alcohol. Tie a piece of cloth quite securely around the first joint and then with a quick thrust of the needle puncture the skin. A drop of blood will quickly collect. This should be transferred to a glass slide. A cover glass which has had vaseline applied to its edges should be placed over the drop in order to seal it.

2. Place the slide on the microscope and observe first with a low magnification. Each pupil should observe the experiment under low and then under higher magnification.

Questions. Can you distinguish the liquid of the blood from the solid bodies (corpuscles)? What is the shape and nature of the corpuscles? In what parts of the blood is most of the coloring matter?

Suggestions for report. Write a brief description of the composition of the blood, using any references you have read to supplement your observations.

Reference work. Read sections 341 to 350.

Optional problems. Allow the arm to hang downward; grip the arm tightly above the elbow and note the location and appearance