Organs and Processes of Digestion : Part 9

Physiology and Hygiene for Secondary Schools
by Francis M. Walters

(Page 18 of 31)

7. Find in the center of the coils of small intestine a long, slender body having the appearance of a gland. This is the beginning of the thoracic duct and is called the receptacle of the chyle. From this the thoracic duct rapidly narrows until it forms a tiny tube difficult to trace in a small animal.

8. Cut away about two inches of the small intestine from the remainder, having first tied the tube on the two sides of the section removed. Split it open for a part of its length, and wash out its contents. Observe its coats. Place it in a shallow vessel containing water, and examine the mucous membrane with a lens to find the villi. Make a drawing of this section, showing the coats.

9. Study the connection of the small intestine with the large. Split them open at the place of union, wash out the contents, and examine the ileo-cecal valve.

10. Observe the size, shape, and position of the kidneys. Do they lie in front of or back of the peritoneum? Do they lie exactly opposite each other? Note the connection of each kidney with the aorta and the inferior vena cava by the renal artery and the renal vein. Find a slender tube, the ureter, running from each kidney to the bladder. Do the ureters connect with the top or with the base of the bladder? Show by a sketch the connection of the kidneys with the large blood vessels and the bladder.

To demonstrate the Teeth. - Procure from the dentist a collection of different kinds of teeth, both sound and decayed.

a. Examine external surfaces of different kinds of teeth, noting general shape, cutting or grinding surfaces, etc. Make a drawing of an incisor and also of a molar.

b. After soaking some of the teeth for a couple of days in warm water saw one of them in two lengthwise, and another in two crosswise, and smooth the cut surfaces with fine emery or sand paper. Examine both kinds of sections, noting arrangement and extent of dentine, enamel, and pulp. Make drawings.

c. Examine a decayed tooth. Which substance of the tooth appears to decay most readily? Why is it necessary to cut away a part of the tooth before filling?

d. Test the effect of acids upon the teeth by leaving a tooth over night in a mixture of one part hydrochloric acid to four parts water, and by leaving a second tooth for a couple of days in strong vinegar. Examine the teeth exposed to the action of acids, noting results.

To show the Importance of Mastication. - Fill two tumblers each half full of water. Into one put a lump of rock salt. Into the other place an equal amount of salt that has been finely pulverized. Which dissolves first and why?

To illustrate Acid and Alkaline Reactions. - To a tumbler half full of water add a teaspoonful of hydrochloric or other acid, as vinegar. To a second tumbler half full of water add an equal amount of cooking soda. Taste each liquid, noting the sour taste of the acid, and the alkaline taste of the soda. Hold a piece of red litmus paper in the soda solution, noting that it is turned blue. Then hold a piece of blue litmus paper in the acid solution, noting that it is turned red. Add acid to the soda solution, and soda to the acid solution, until the conditions are reversed, testing with the red and blue litmus papers.

Hold, for a minute or longer, a narrow strip of red litmus paper in the mouth, noting any change in the color of the paper. Repeat, using blue litmus paper. What effect, if any, has the saliva upon the color of the papers? Has the mouth an acid or an alkaline reaction?

To show the Action of Saliva on Starch. - 1 (Optional). Prepare starch paste by mixing half a teaspoonful of starch in half a pint of water and heating the mixture to boiling. Place some of this in a test tube and thin it by adding more water. Then add a small drop of iodine solution to the solution of starch. It should turn a deep blue color. This is the test for starch.

Now collect from the mouth, in a clean test tube, two or three teaspoonfuls of saliva. Add portions of this to small amounts of fresh starch solution in two test tubes. Let the tubes stand for five or ten minutes surrounded by water having about the temperature of the body. Test for changes that have occurred as follows:

a. To one tube add a little of the iodine solution. If it does not turn blue, it shows that the starch has been converted into some other substance by the saliva, b. To the other tube add a few drops of a very dilute solution of copper sulfate. Then add sodium (or potassium) hydroxide, a few drops at a time, until the precipitate which first forms dissolves and turns a deep blue. Then gradually heat the upper portion of the liquid to boiling. If it turns an orange or yellowish red color, the presence of a form of sugar (maltose or dextrose) is proved. See page 136.

2. Hold some powdered starch in the mouth until it completely dissolves and observe that it gradually acquires a sweetish taste. This shows the change of starch into sugar.

To illustrate the Action of the Gastric Juice. - Add to a tumbler two thirds full of water as much scale pepsin (obtained from a drug store) as will stay on the end of the large blade of a penknife. Then add enough hydrochloric acid to give a slightly sour taste. Place in the artificial gastric juice therefore prepared some boiled white of egg which has been finely divided by pressing it through a piece of wire gauze. Also drop in a single large lump. Keep in a warm place (about the temperature of the body) for several hours or a day, examining from time to time. What is the general effect of the artificial gastric juice upon the egg?

To illustrate Effect of Alcohol upon Gastric Digestion. - Prepare a tumbler half full of artificial gastric juice as in the above experiment, and add 10 cubic centimeters of this to each of six clean test tubes bearing labels. To five of the tubes add alcohol from a burette as follows: (1) .5 c.c., (2) 1 c.c., (3) 1.5 c.c., (4) 2 c.c., and (5) 3 c.c., leaving one tube without alcohol. Now add to each tube about 1/4 gram of finely divided white of egg from the experiment above, and place all of the tubes in a beaker half full of water. Keep the water a little above the temperature of the body for several hours, examining the tubes at intervals to note the progress of digestion. Inferences.

D.C. Heath and Co. - Publishers
Original copyright 1909