CHAPTER VII

FOOD AND DIGESTION

_Experiment 1._ =Tests for Acid, Alkaline, and Neutral Substances.=--Repeat tests described in General Introduction.[6]

[6] See also Peabody’s “Laboratory Exercises in Physiology,” Holt, N.Y.

_Experiment 2._ =Test for Starch.=--See General Introduction.

_Experiment 3._ =Test for Grape Sugar.=--See General Introduction.

_Experiment 4._ =Test for Proteid.=--See General Introduction.

_Experiment 5._ =Test for Fats.=--See General Introduction.

_Experiment 6._ =Human Teeth.=--Study the form of teeth from every part of the mouth. Get a handful from a dentist. Break some of the teeth to make out their structure. Classify them. Draw section, enlarged.

_Experiment 7._ =Study of the Teeth.= (At home.)--Sit with the back to the light and look into a mirror, with the mouth wide open. Do you see the four kinds of teeth named in text? Which are fitted for cutting? Which for grinding? Are any suited for tearing? Are any of the teeth pointed? What is the difference in the bicuspids and molars? Are there any decayed places? Are the teeth clean? Are the so-called canine teeth so long that they project beyond the line of the other teeth, as they do in a dog? Do the edges of the upper and lower incisors meet when the mouth is closed, or do they miss each other like the blades of scissors? How many roots has each lower tooth? (See Fig. 92.). Which tooth has the longest root?

_Experiment 8._ =Structure of Mammalian Stomach.=--Get a piece of tripe from the market. Study its several coats. The velvety inner coat is covered with mucous membrane. (Photomicrograph, Fig. 95.)

_Experiment 9._ =Model of Human Food Tube.=--Make a model of the food tube out of yellow cambric, giving to each organ its correct size. Follow the dimensions given in text.

=Necessity for Foods.=--Growing plants and growing animals need new material to enable them to _increase in size or grow_. Plants never cease to grow while they live; most mammals attain their full size in one fifth of the time occupied by their whole lives. (By this rule how long ought man to live?) Animals, moreover, _move from place to place_, and _work_ with their muscles. The energy for this comes from the food they eat. Plants do not use food for this purpose. Another need for food comes from the _necessity for heat_ in all living things. The activities of animals cause the tissues to wear out, or break down, and food furnishes material with which new living matter is built up by the cells and the _tissues repaired_. We have already stated the rôle of oxygen in setting free energy in the living substance of the cell by oxidizing it. There is no furnace in the body as in an engine, but the oxidation occurs in the cells themselves and the fuel is built up into living matter by the cells before it is oxidized. Plants must lift mineral from the inorganic to the organic world before it can be food for animals. Plants can assimilate minerals; animals cannot. The body cannot make bone out of limewater. The iron in iron tonics cannot be used. Iron makes the grain brown, and the peach red. There is ten times as much iron in our food as the body needs.

State four reasons why animals need food. Which of these reasons is very powerful with plants? Least powerful? Absent altogether? Why is constant breathing necessary for life? When is breathing more rapid? Why? People who lead what kind of lives usually have poor appetites? Good appetites? Why? What was the first distinct organ evolved by animals? (Animal Biology, Chap. IV.)

=The Body is a Machine for transferring Energy.=--Energy cannot be destroyed, but it can be transferred and changed in form. When a coin is rubbed on the table, muscular energy, supplied by oxidation in the muscle, produces the motion. Friction may change motion into heat, and the coin will become very hot. The uniting of food and oxygen in the cells of the body gives the heat and motion (energy) of the body. Only substances which will oxidize, or burn, are true foods. Water, salt, and carbon dioxid will not burn; hence, they cannot give rise to energy in the body. But the sun energy, acting in the green leaf, tears apart the carbon from the oxygen (Plant Biology, Chap. XIII), sets free the oxygen, and the carbon is stored in starch for future burning. Sunshine is energy (light and heat). The sun sustains the life of plants and through them the life of animals. The oxidation in the body is so slow that it can hardly be called a burning, but it is faster than the oxidation of iron in rusting or of wood in rotting, and is about equal to the continual burning of two candles.

=The Four Kinds of Nutrients, or Food Stuffs.=--The _kinds of food which we eat seem to be numberless, but they contain only four kinds of food stuffs_,--starches, fats, proteids, and minerals. Many foods contain all four classes of food stuffs. Milk contains sugar (a changed form of starch), cream (a fat), curd (a proteid), and water (a mineral). Oatmeal contains starch, oil, gluten, and water.

USES OF THE NUTRIENTS, OR FOOD STUFFS

1. Proteids. The tissue-building foods (also of value as fuel). 2. Starches (and sugars) } } Energy and heat (fuel) and fat producing } foods. 3. Fats (and oils) } 4. Minerals (water, salt). Important aids in using other foods.

=Relative Fuel Value.=--A pound of fat produces as much heat in the body as 2.3 lb. of proteid or 2.3 lb. of starch, the last two having equal fuel value in the body.

=Starch and the sugars= are closely related; starch readily changes into sugar. They contain much carbon and are called =carbohydrates=. Starch is especially abundant in grains, seeds, and fleshy roots (Fig. 88). The sugar in ripe fruit and in honey is called _fruit sugar_. _Milk sugar_ is found in sweet milk. _Grape sugar_ is found in grapes and honey; the small grains seen in raisins consist of grape sugar; it can also be prepared artificially from starch. _Cane sugar_ is found in cane, in sap of the maple, and in the sugar beet (Exps. 2, 3).

[Illustration: FIG. 88.--A TINY BIT OF POTATO, highly magnified, showing cells filled with grains of starch. Cooking bursts these cells.]

=Fats= include the fats and oils found in milk, flesh, and plants. A fat, such as tallow, is solid at the ordinary temperature; while an oil, such as olive oil, is liquid at the same temperature. Tallow was oil while it was in the warm body of the ox. Sugar is transformed into fatty tissue as readily as is fatty food itself.

=Proteids= are the only foods that contain the tissue-building nitrogen. Protoplasm cannot be formed without nitrogen. We do not often see a pure proteid food, for this food stuff is not so readily separated from foods containing it as are starch, sugar, and fat. Albu_men_, or white-of-egg, is proteid united with four times its weight of water. Pure proteid is also called albu_min_. Coagulation by heat is one test for proteid (Exp. 4). These are the names of proteids, or albumins, found in several common foods: _casein_, the curd or cheesy part of milk; _myosin_ of lean meat; _fibrin_ in blood; _legumin_ in beans and peas; _gluten_, or the sticky part of wet flour; _gelatin_ in bones. Proteid is valuable to the body as fuel as well as a tissue builder. We could burn beans and peas as well as the strictly fuel foods, starch and fat, in an engine, and get heat to move the engine. If one takes up athletics or hard physical labor, he should increase the amount of fats and carbohydrates eaten, but not of proteid. Muscular activity increases the carbon waste but not the nitrogen waste of the body.

=Minerals.=--The iron of the blood and the mineral salts in bone (carbonate and phosphate of lime) must enter the body in organic form in order to be used. Water and salt are mineral foods. The body is about two thirds water. The cells must do their work under water. They cannot live when dried. Water enables the blood to flow; and the blood is not only the feeder, but also the washer and cleanser of the tissues. Some persons get out of the habit of drinking plenty of water, and their health suffers thereby. In such a case drinking plenty of water will be safer and more effective than taking poisonous drugs to restore health.

=Adulteration of Food.=--Sometimes _cheaper materials_, of little or no value as food but of no great injury to health, are added to foods. _Examples:_ water added to milk, sawdust to ground spices, chicory to coffee, glucose to maple syrup. Other forms of adulteration not only cheat the purse but _tend to destroy health_, or actually do so. _Examples:_ Boracic acid or formalin added to milk to prevent souring, copper to canned peas, etc., to give a bright green color; salicylic acid or borax used in minute quantities as a preservative with canned corn, tomatoes, etc.; acids added to “apple” vinegar; dried fruit treated with sulphur to prevent a dull color. Pure food laws tend to repress these evils. It is best to buy foods in their original form. For instance, lemons are more reliable than vinegar. A bit of lemon at each plate, in households that can afford it, is far preferable to vinegar. We should always buy from neighbors when possible. Farmers and gardeners should do their own drying and canning. For purity of water, see Chap. X.

=The Daily Ration.=--_A quarter of a pound_ (4 oz.) _of proteid foods and one pound_ (16 oz.) _of fuel foods_ (total 20 oz. of water-free foods) are needed to replace the daily =waste= of the body. Hence a _balanced ration_ has proteid and fuel food in the ratio of 4 to 16, or 1 to 4. But recent experiments at Yale University indicate that 2 oz. of proteid daily are more strengthening than four.

_Appetite is a perfect guide for those who lead an active life and eat slowly of simple food._ Highly seasoned food and complex mixtures deprave the appetite; it then leads astray, instead of guiding safely. Of course the appetite cannot guide one to eat the right kind and quantity of food at a table where the food lacks any of the four necessary food stuffs, or where innutritious or indigestible food is provided. It is well to select one food for a meal because it is rich in proteids, another because it is rich in fat, and the third because it is rich in starch or sugar. (See table, p. 95.) Intelligence in regard to diet enables a housekeeper to provide nourishing food for less money than an ignorant housekeeper often pays for food deficient in nourishing qualities.

=A Balanced Ration.=--A deficiency of starch may be supplied by an excess of fat or sugar. It is most essential to provide proteid as it cannot be replaced by any other food stuff. An excess of proteid is most harmful. An excess of starch or fat is oxidized into water and carbon dioxid, which are harmless waste products; an excess of proteid is changed into urea which may become harmful by overworking the liver and kidneys which excrete it.

COMPOSITION OF ONE OUNCE OF VARIOUS FOODS IN FRACTIONS OF AN OUNCE

========================+=======+=======+========+=======+=====+===== | | | CARBO- | | MIN-| | PRO- | | HY- | | ERAL|WOODY | TEIDS | FATS | DRATES | WATER |SALTS|FIBER ------------------------+-------+-------+--------+-------+-----+----- =Daily Ration= |=4 oz.=|=2 oz.=|=14 oz.=|=2 qt.=| | =0= | | | | | | I. NUTS. | | | | | | Pecan | .103 | .708 | .143 | .03 | .017| Walnut | .158 | .574 | .16 | .03 | .014| Almonds | .235 | .53 | .12 | .078 | | Cocoanut | .056 | .51 | | .35 | | .04 Chestnut | .037 | .02 | .38 | .54 | .009| .02 | | | | | | II. FRUITS. | | | Sugar | | | Peach | .007 | | .045 | .85 | .007| .04 Apple | .004 | | .072 | .84 | .005| .05 Blackberry | .005 | | .040 | .86 | .004| .01 Cherry | .005 | | .10 | .84 | .007| .02 Grape | .125 | | .15 | .70 | .005| Fig (dried) | .040 | .014 | .50 | | | Banana | .050 | | .20 | .75 | | | | | | | | III. ANIMAL FOOD. | | | | | | Lean beef | .20 | .035 | .009 | .75 | .016| Fat pork | .098 | .489 | | .390 | .023| Smoked ham | .25 | .365 | | .278 | .101| Whitefish | .181 | .029 | | .780 | .010| Poultry | .210 | .038 | | .740 | .012| Oysters | .175 | .005 | | .800 | .015| Cow’s milk | .035 | .040 | .040 | .870 | .007| Eggs | .125 | .120 | | .735 | .010| Cheese | .335 | .243 | | .368 | .054| Butter | .003 | .910 | | .060 | .021| | | | | | | IV. PODS OR LEGUMES. | | | Starch | | | Beans | .25 | .020 | .52 | .125 | .035| .060 Peas | .217 | .019 | .577 | .12 | .028| .032 Peanuts | .2947 | .465 | .162 | .02 | .028| .043 | | | | | | V. GRAINS. | | | | | | Wheat flour (white)| .110 | .020 | .703 | .150 | .017| .003 Wheat bread | .080 | .015 | .490 | .400 | .012| .003 Oatmeal | .126 | .056 | .630 | .150 | .030| .016 Maize (corn) | .100 | .067 | .706 | .135 | .014| .015 Rice | .050 | .008 | .832 | .100 | .005| .040 | | | | | | VI. VEGETABLES. | | | | | | Potatoes | .012 | .001 | .205 | .767 | .009| .006 Cabbage | .02 | .030 | .058 | .910 | .007| .015 ========================+=======+=======+========+=======+=====+=====

=Studies based on Table.=--What nuts are rich in proteids? What fruits? What animal foods? What legumes? What grains? What foods are rich in fats? What are rich in carbohydrates? Which grains have much starch? Which nut? Which fruits have much sugar? A family was living chiefly on corn bread, potatoes, syrup, cakes, and sweetmeats: what two of the four food stuffs were deficient in their diet? Another family lived chiefly on fat pork, bread, rice, vegetables, and fruit: which food stuff was deficient? A dozen eggs weigh 1¹⁄₂ lb. Which give cheaper nourishment, eggs at 15 cents a dozen or beef at 15 cents a pound? Which is cheapest among the foods abounding in proteid? Fat? Carbohydrates? Which is cheaper food, a pound of beef at 20 cents or a pound of pecans at the same price? (Fig. 101.) What food contains most water? Least water? Which of the foods abounding in proteid is costliest? Cheapest? Notice that nearly all foods containing much proteid are costly. Water and woody fiber are not counted as nutriment. What weight of nutriment in 1 oz. of cow’s milk? If a quart of whole milk costs 12 cts., what is a quart of skimmed milk worth?

=How the Right Proportions of Fuel Foods and Proteid are reached by Different Nations.=--Milk has an excess of nitrogen, and oatmeal an excess of carbon; oatmeal and milk form a popular food with the Scotch. Potatoes are mostly starch and water, and an Irishman who tried to live on potatoes alone would have to eat seven pounds a day to get enough proteid. The Irish peasant keeps a cow and chickens; by eating milk and eggs he gets along on half the amount of potatoes named above. The Mexicans eat bread made of corn meal, and supply the proteid by using beans as a constant article of diet. Hundreds of millions of people in Asia (the Hindus, Chinese, and others) subsist mainly on rice, which contains only five per cent of proteid and no fat; the chief addition they make is butter, or other fat, and beans, which contain vegetable proteid.

=Outline of Digestion.=--The food is made soluble in the alimentary canal and is absorbed by the blood vessels and lymphatics in its walls. This canal is about thirty feet long (Figs. 89, 90) and consists of--

(1) The =mouth=, where the food remains about a minute, while it is chewed and mixed with the _saliva_; the saliva changes a portion of the _starch_ to malt sugar.

(2) The =gullet=, a tube nine inches long, running from mouth to stomach and lying in front of the spinal column.

[Illustration: =Illustrated Study of Food Tract.=

FIG. 89.--ORGANS OF TRUNK from the side.

_L_, larynx; _th_, thyroid gland; _T_, trachea; _St_, breastbone; _C_, heart; _D_, diaphragm; _F_, liver; _E_, stomach; _I_, intestine; _Co_, colon; _R_, rectum; _V_, bladder.

=Question:= Parts of which organs are farther back than spinal column? Compare this figure with colored Fig. 6.

FIG. 90.--DIGESTIVE ORGANS, from the front (liver turned up).

1, gullet; 2, stomach; 3, spleen; 4, pancreas; 5, liver (turned upward); 6, gall bladder; 7, 8, 9, small intestine; 9′, junction of small with large intestine; 10, caecum (blind sac); 11, vermiform appendix; 12, 12′, 12″, ascending, transverse, and descending colon; 13, rectum (straight) just below S-shaped flexure of colon.

=Question:= Compare with Fig. 89, and colored Fig. 6.]

(3) The =stomach=, a large pouch where the food is stored, and from which it passes in the course of several hours, having become semi-liquid, and the _proteids_ having been partly digested by the _gastric juice_, an acid secretion from the small glands in the stomach walls.

(4) The =small intestine=, a narrow tube more than twenty feet long, where the _fats_ are acted upon for the first time, and where the _starches_ and _proteids_ are also acted upon, and where, after about ten hours, the digestion of the three classes of foods is completed by _pancreatic juice_ from the _pancreas_, and _bile_ from the _liver_.

(5) The =large intestine=, about five feet long, where the last remnant of nutriment is _absorbed_, and the _indigestible materials_ in the food are gathered together (Exp. 9).

=The Teeth.=--The main body of the tooth consists of bone-like _dentine_, or ivory. Hard, shining _enamel_ protects the crown, or visible portion. The part of the tooth beneath the gum is called the _neck_, and the part in the bony socket, is called the _root_. The enamel ends just beneath the gum, where it is overlapped by _cement_ of the root. There is a pulp cavity in every tooth (Fig. 91); it contains _pulp_ made up of connective tissue, with nerves and blood vessels which enter at the tip of the root (Exp. 6).

[Illustration: FIG. 91.--CANINE TOOTH CUT LENGTHWISE.]

The _temporary_ set of teeth is completed at about two years of age and consists of twenty teeth. The teeth cannot grow as the jaw grows, and soon a larger and _permanent_ set starts to growing deeper in the jaw. At the age of twelve or thirteen years all the permanent set have appeared except the four wisdom teeth, which appear between the ages of seventeen and twenty-five. The second set not only replaces the twenty of the first set, but to fill the larger jaws twelve molars are added, three at the back in each half jaw, making thirty-two teeth in the second set (Exp. 7). The teeth in each quarter of the mouth, named in order from the front, are: two _incisors_, one _canine_, two _premolars_, three _molars_.

[Illustration: FIG. 92.--THE PERMANENT TEETH in right half of lower jaw.]

[Illustration: FIG. 93.--UPPER JAW WITH TEETH.]

=Care of the Teeth.=--The best way to care for the teeth is _to keep the digestion perfect_. Perfect digestion tends to preserve the teeth, and sound teeth tend to keep the digestion perfect. The teeth should be _washed regularly_. Prepared chalk is the best dentifrice. Do not rub across, but from gums to teeth, to prevent rubbing the gums loose from the teeth. An unclean brush may harbor germs. _Toothpicks_ and dental floss are useful. If one eats only soft food, in which the mill and the cooking stove have left no work for the teeth, the teeth will decay; for it seems to be a law of nature that useless organs are removed. The pressure from _chewing hard food is an aid_ to the teeth by helping the circulation and nerves in the pulp. To take a _very hot or very cold_ drink into the mouth may cause the _enamel to crack_. If a tooth aches, or a small decayed place is found in it, a dentist should be consulted at once. A tooth is so valuable to the health that no tooth should be extracted when it can be saved.

=The process of digestion= consists in liquefying the food that it may pass through the walls of the food tube into the blood, and through the walls of the blood vessels into the tissues. It is accomplished: (1) by _mechanical_ means, including the chewing muscles, the teeth, and three layers of muscles in the walls of the food tube; (2) by _chemical_ means, or the action of alkalies and acids upon the food; (3) by _organic_ agency, or the action of ferments. A _ferment_ (or _enzyme_) is a vegetable substance which has the power of producing a chemical change in large quantities of substance brought in contact with it, without being itself changed. There is one ferment secreted in the mouth, two in the stomach, and three in the small intestine.

=Digestion in the Mouth.=--_Saliva_ is formed by six glands: one in the cheek in front of each ear, one at the angle of each lower jaw, and one pair is beneath the tongue. Each gland opens into the mouth by a duct. Saliva is ropy because it is mixed with mucus formed by the mucous membrane lining the mouth; it usually contains air bubbles. There is a ferment in the saliva called _ptyalin_, which has the power of changing starch to malt sugar. If a bit of bread is chewed for a long time, it becomes sweet, because some of the _starch is changed to sugar_. The flow of saliva is caused by chewing, or by the sight, or even the thought, of agreeable food. Dryness of food is by far more powerful than anything else in causing the saliva to flow. Saliva is secreted only one fourth as fast when eating oatmeal and milk as when eating dry toast (Fig. 94).

[Illustration: FIG. 94.--CELLS OF A SALIVARY GLAND

_A_, after rest, full of granules; _B_, after short activity; _C_, after prolonged activity, cells shriveled and granules lost.]

Starchy grains and fruits were eaten by early man without cooking, and required more chewing than sweet, ripe fruits or oils or proteids. Hence the saliva was given the power of acting upon the starch, for it must remain in the mouth longer. The saliva is alkaline; and if the food is not thoroughly mixed with it, the stomach digestion will also be imperfect, for the _alkaline saliva is necessary to excite an abundant flow of gastric juice in the stomach_ (Exp. 1).

=Eating slowly= is difficult because of the grinding and cooking of food; hence the common practice of overeating. To eat slowly (1) do not take large mouthfuls; (2) do not take a second morsel until the first has been swallowed; (3) sit erect or lean back after putting food into the mouth; (4) the hands should lie idle most of the time. To lean forward and keep food traveling to the mouth like coal into a chute means overeating with all its bad effects.

_Chewing gum_ is a coarse and impolite habit, and wastes the saliva, besides weakening the glands and irritating the stomach by the saliva that is continually swallowed. _Chewing tobacco_ has several of these disadvantages, besides allowing the poison in the tobacco to be absorbed by the mucous lining of the mouth.

=The pharynx= (far′inks), =or throat=, is a muscular bag suspended behind the nose and mouth. (See Fig. 89, also Fig. 83.) There are _seven openings_ into the pharynx: two from the nostrils, two from the ears, one each from the mouth, larynx, and gullet. Which of these openings are downward? Forward? Lateral?

=The gullet= (or esophagus) is a muscular tube about nine inches long. (See Fig. 89.) Like the rest of the food tube, it is lined with mucous membrane. It has two layers of muscles in its walls, the fibers of one layer running lengthwise, and the fibers of the other layer being circular. In _swallowing_, the food does not fall down the gullet of its own weight, but _the circular bands of muscle in front of the food relax_, and _those behind it contract and push it on into the stomach_. This wavelike motion is called _peristalsis_.

=The stomach=, the greatest enlargement of the food tube, is like _a large bag lying sideways_. It lies to the left side of the abdomen. The walls of the stomach consist chiefly of _muscular fibers which run lengthwise, crosswise, and slantwise_, making three coats (Exp. 7, also Fig. 95). As soon as the food reaches the stomach, the layers of muscles begin to contract, changing the size of the stomach, first in length, then in breadth, thus churning the food to and fro, and mixing it with the gastric juice, a fluid more active than the saliva. For as the food enters the stomach, the mucous membrane lining it turns a bright red, and many little gastric glands in the lining begin to secrete gastric juice.

[Illustration: FIG. 95.--MUSCULAR AND OTHER LAYERS IN WALL OF STOMACH.

1, mucous lining; 2, layer of blood vessels and connective tissue; 3, muscular layers (involuntary muscles); 4, connective-tissue fibers. (Peabody.)]

=Digestion in the Stomach.=--The stomach churns the food from two to four hours after the meal, according to the kind of food eaten, the way it has been cooked, and the thoroughness with which it has been chewed. The _gastric juice_ is chiefly water, and contains two ferments called _pepsin_ and _rennin_, and a small quantity of _hydrochloric acid_. Rennin acts upon the curd of milk, and is abundant only during infancy. Hydrochloric acid kills germs that may enter the stomach, and changes the food which has been made alkaline by the saliva into an acid condition (Exp. 1). This enables the _pepsin to act upon the proteid part of the food_, for pepsin will not act while the food is alkaline. Gastric juice _digests lean meat_, which is a proteid food, by first dissolving the connective tissue that holds the fibers in place, and they fall apart; it then acts upon the fibers separately and makes them soluble. Like human fatty tissue (Fig. 14), _fat meat_ consists of cells filled with fat and held together by threads of connective tissue. The cell walls and the threads, both being proteid, are soon dissolved by the gastric juice, and the free fat is melted into oil, but still undigested. The food is reduced in the stomach to a creamy, half-fluid mass called _chyme_. Where the stomach opens into the small intestine, there is a folding in or narrowing of the tube so as to form a kind of valve called the _pylorus_. After the food has been changed to chyme, this fold relaxes every minute or two, and allows some of the chyme to escape into the intestine.

[Illustration: FIG. 96.--A PORTION OF SMALL INTESTINE cut open to show the folds in its lining.]

=The small intestine= is about one inch in diameter and twenty feet long, with many coils and turns in its course (Fig. 90). Its mucous lining is wrinkled into numerous _folds_ in order to increase the secreting and absorbing surface (Fig. 96). On and between the folds are thousands of little threadlike projections called _villi_ (Fig. 97). In each villus are found fine capillaries and a small lymphatic called a _lacteal_ (colored Fig. 2). The villi are so thick that they make the lining of the intestine like velvet, and enormously increase the absorbing surface.

[Illustration: FIG. 97.--LINING OF SMALL INTESTINE, magnified, showing villi and mouths of intestinal glands.]

=Digestion in the Small Intestine.=--This is by far the most active and important of the digestive organs. The mouth digests a small part of the starch, and the stomach digests a small part of the proteid; _the small intestine digests most of the starch, most of the proteid, and all of the fats_. The food is in the mouth a few minutes, and in the stomach two or three hours; it is in the small intestine ten or twelve hours. There are thousands of small glands called _intestinal glands_ that open between the villi (Fig. 97) and secrete the intestinal juice, which _digests cane sugar_. Besides these, there are two very large and active glands, the pancreas and liver, which empty into the intestine by ducts.

=The Pancreas.=--The small intestine is the most important of the digestive organs, chiefly because it receives the secretion from the pancreas, the most important of digestive glands. The pancreas is a _long_, _flat_, _pinkish gland situated behind the stomach_ (see Fig. 90). The pancreatic juice contains _three powerful ferments_, one of which (amylopsin) digests the starches, another (trypsin) digests proteids, and the third (steapsin), with the aid of the bile, breaks up the fats into tiny globules. Fat in small globules floating in a liquid is called an _emulsion_; fresh milk is an emulsion of cream (Fig. 98). Fat is not changed to another substance by digestion, but it is emulsified, and in this condition it readily passes through the walls of the intestines and is absorbed by the lymphatics called _lacteals_ (colored Fig. 5) found in the villi. It then ascends through the _thoracic duct_ to a large vein at the left side of the neck (Fig. 100). _The digested proteid, starch, and sugar pass into the capillaries of the portal vein, and go to the liver_ on their way to the general circulation (Fig. 100). The portal circulation empties into the large ascending vein leading to the right auricle (Fig. 100).

[Illustration: FIG. 98.--JUNCTION OF LARGE AND SMALL INTESTINE.]

=The Liver.=--This large, chocolate-colored gland is located just beneath the diaphragm on the right side (Fig. 90, colored Fig. 6). It is on a level with the stomach, which it partly overlaps in front. The liver has three important functions: (1) _It is a storeroom_; digested sugar and starch are stored in it as a substance called _liver starch_ (or glȳ′cogen). (2) _It is a guardian_, and destroys poisonous substances which may be swallowed, and which would otherwise enter the blood. Twice as much morphine or other poison is necessary to kill a man when it is taken by the mouth and passes through the liver as when it is injected through the skin. Alcohol, morphine, coffee, and drugs are partly burned up in the liver. (3) _It is a gland_, and secretes bile. The bile is made chiefly from waste products and impurities in the blood; it is an excretion. Although an excretion, it is of use on its way out of the body. It is alkaline and helps to neutralize the acid in the chyme; it excites the peristalsis, or wavelike motion, of the intestines, and it aids the pancreatic juice to emulsify the fats.

[Illustration: FIG. 99.--DIAGRAM OF TRUNK to show the many folds of the PERITONEUM supporting the liver, stomach, and intestines.]

=The large intestine, or colon=, is about two and one half inches in diameter and five feet long. _The small intestine joins it in the lower right side of the abdomen_ (Fig. 90). There is a fold, or valve, at the juncture, and just below the juncture there is a tube attached to the large intestine, called the _appendix_, which sometimes becomes inflamed, causing a disease called _appendicitis_ (Figs. 90, 98). The appendix is a vestigial (_vestigium_, trace) or rudimentary organ, long since useless. _Absorption_ of the watery part of the food continues in the colon, but the colon secretes no digestive fluid. The undigested and innutritious parts of the food are regularly cast out of the colon.[7] The _peritone′um_ is a membrane with many folds that supports the food tube (Fig. 99).

[7] No truly refined person will allow business, pleasure, haste, or neglect to interfere with regular attention to emptying the colon. This is more necessary for real cleanliness than regular baths.

=Absorption.=--The way in which the various digested foods are absorbed has been stated in several preceding topics. What is the name of the organs of absorption in the small intestine? Which of the following pass into the lacteals, and which into the capillaries of the portal vein: sugar, digested proteid, emulsified fats? Water and salt need no digestion, and are absorbed all along the food tube, the absorption beginning even in the mouth. What reasons can you give for the absorption of food being many times greater in the small intestine than in the stomach? Through what large tube is the fat carried in passing from the lacteals to the veins? Into what large vein do all the capillaries that take part in absorption empty? (Colored Fig. 5.) What is the provision for storing the sugar so that it will not pass suddenly into the blood after a meal, but may be given to the blood gradually? Food is assimilated, or changed into living matter (protoplasm), in the cells. Blood and lymph (except the white corpuscles) are not living matter. (Fig. 100.)

[Illustration: FIG. 100.--THE TWO PATHS OF FOOD ABSORPTION. Thoracic duct (for fats); through the portal vein and liver (for all other foods).]

THOUGHT QUESTIONS. =The Digestive Organs.=--=1.= In which of the digestive organs is only one kind of secretion furnished by glands? =2.= In which organ are three kinds of secretions furnished by glands? =3.= Which class of food goes through the lymphatics? =4.= Which classes of foods go through the liver? =5.= Which classes of foods are digested in only one organ? =6.= Which classes of foods are digested in two organs? =7.= Which division of the food tube is longest? Broadest? Least active? Most active? =8.= Soup is absorbed quickly; why does eating it at the beginning of a meal tend to prevent overeating?

=Hygienic Habits of Eating.=--In hot weather much blood goes to the skin and little to the food tube, and digestion is less vigorous. Hearty eaters suffer from heat in summer because of much fuel, and because the blood is kept away from the skin where it would become cool and then cool the whole body. Some persons believe that the stomach should be humored and given nothing that it digests with difficulty; others believe that it should be gradually trained to digest any nutritious food. Some believe that no animal food should be eaten; others believe that animal food is as valuable as any. Some believe that all food should be eaten raw, but this would irritate a delicate stomach. It is doubtless best to use no stimulant, either tea or coffee, pepper or alcohol. Some eat fast and drink freely at meals; it is better to eat slowly and drink very little or none at all while eating, nor soon afterwards. Some eat five meals a day, and between meals if anything that tastes good is offered them; others eat only two or three meals a day, and never between meals, thus allowing the digestive organs time to rest. Some omit breakfast and some omit supper. Some prepare most of the food with grease; this is a tax upon digestion. Physical workers often believe in eating the peelings and seeds of fruits, and partaking freely of weedy vegetables, such as cabbage, turnip tops, string beans. Mental workers usually try to reject all woody fiber and indigestible pulp from the food before swallowing it. Some eat large quantities of food and digest a small portion; others eat little but digest nearly all.

=The Power of Adaptation of the Digestive Organs.=--Of course some habits of eating are better for the health than others, yet the undesirable ways often bring so little injury that they are not discontinued. This shows that the food tube has great powers of adaptation to different conditions. But there are limits to this adaptation; there is an old saying that what is one man’s meat is another man’s poison. A brain worker cannot follow the same diet as a field hand without working at a disadvantage. An irritable stomach may be injured by coarse food that would furnish only a healthful stimulus to a less sensitive one. A business man who has little leisure at noon should take the heaviest meal after business hours. In general, it may be said that it does not make so much difference _what_ is eaten as _how_ it is eaten, and _how much_ is eaten. There is a common tendency to exaggerate the importance of dietetics.

THOUGHT QUESTIONS. =Indigestion.=--I. _A Fetid Breath._ =1.= Name three causes of bad breath. =2.= Let us investigate whether indigestion could cause a bad breath. In what kind (two qualities) of weather does meat spoil the quickest? =3.= Suppose that meat or other food is put into a stomach with its gastric glands exhausted and its muscular walls tired out, what will be the rate of digestion, and what might happen to the food? =4.= Odorous contents of the stomach (_e.g._ onion) can be taken by the blood to the lungs where it will taint the breath.

After answering the above questions, write in a few words how indigestion may cause a bad breath.

II. _A Coated or Foul Tongue._ =1.= When the doctor visits you, at what does he first look? =2.= What sometimes forms on old bread? (p. 158.) =3.= Do you think such a growth possible on undigested bread in the stomach? =4.= The microscope shows the coating on the bread to be a growth of mold. If it forms on the walls of the stomach, it may extend to what?

III. _Stomach Ache._ =1.= How can you tell whether fruit preserved in a sealed glass jar is fermenting? =2.= What connection is there between belching after eating too freely of sweet or starchy food, and the observation above? =3.= A muscle gives pain when it is stretched. Why does belching sometimes give relief to an uneasy stomach? =4.= Can you, by using these facts, explain a cause of stomach ache?

=For what Kind of Man were the Human Digestive Organs created?=--That food is best to which the food tube has been longest accustomed. It would be of the greatest value as a guide to diet if we knew the food eaten by early man during the many ages _when he led a wild life in the open air_. The organs of early man were doubtless perfectly adapted to the life he led. The food tube is adapted to the needs of those long ages, for a few centuries of civilization cannot change the nature of the digestive organs; yet some people disregard natural appetites and try to force the digestive organs to undergo greater changes in a few months than centuries could bring about.

=To test whether an Article of Food belonged to Man’s Original Diet.=--Scientists agree that the human race began in a warm country; that _early man was without gristmills, stoves, or fire, and ate his food raw_. If an article of food is pleasant to the taste in its raw, pure state, there is little doubt that it, or a similar food, was eaten by primitive man before he knew the use of fire in preparing his food. Apply this test to the following foods, underlining those foods that pass the test: apples, bananas, lettuce, turnip greens, turnips, fruits, nuts, beef, fowls, eggs, oysters, green corn, cabbage, pork, watermelons, grains, crabs, fish, white or Irish potatoes, yams, tomatoes.

[Illustration: FIG. 101.--BLACKBOARD DIAGRAM. Amount of nourishment (black) and waste (white) in several foods. (After Latson.)]

=The Order in which Man increased his Bill of Fare.=--Flesh-eating animals have a short food tube, as their food is digested quickly; they have long, pointed teeth for tearing, sharp claws for holding, and a rough tongue for rasping meat from the bones. Man’s even teeth, long food tube, soft and smooth tongue, and flattened nails, indicate that he is suited for a diet largely vegetable (see Table, p. 111). _The race at first probably ate tree fruits_,[8] both nuts and fleshy fruits (Fig. 101). Because of famine, or after migration to colder climates, and after learning the use of fire, the race probably began to use flesh for food. Afterward the hunters became farmers and learned to cultivate grain, which formed a most important addition to the food supply, and made possible a dense population. Coarse, woody foods, like the leaves and stems of herbs, were probably added last of all. Woody fiber (cellulose) can be digested by cattle, but it cannot be digested by man.

[8] See Genesis i. 29. Some raw food should be eaten daily. Pecans are the most digestible of all nuts. A half dozen or more eaten regularly for breakfast will prevent constipation or cure it in ten days or less.

=The Natural Guide in Eating is Taste.= Man should preserve his taste uncorrupted as, next to his conscience, his wisest counselor and friend. It has been developed and transmitted through countless ages as a precious heritage. Simple food is more delicious to people with natural tastes than the most artificial concoctions are to those with perverted taste.

=Animal Food.=--The _flesh_ of animals furnishes proteid and fat (Fig. 102). As cooking coagulates and hardens albumin, raw or half-cooked meat is said to be more digestible than cooked meat; but meat that is not thoroughly cooked is dangerous because it may contain trichinæ (“Animal Biology,” p. 50) and other parasites. Lean meats contain much proteid. Some persons who cannot easily digest starch and sugar because of fermentation eat fat for a fuel food. _Beef tea_ and beef extracts contain but a small part of the proteid in meat and all of the waste matter, including urea.

[Illustration: FIG. 102.--DIAGRAM SHOWING CUTS OF BEEF.

1. sirloin 2. loin 3. rump 4. round 5. top sirloin 6. prime ribs 7. blade 8. chuck 9. neck 10. brisket 11. cross-rib 12. plate 13. navel 14. flank 15. shoulder 16. leg]

=============+=============+=============+=============+============== MAMMALS |CARNIVORA, OR|HERBIVORA, OR|OMNIVORA, OR | FRUGIVORA, OR COMPARED |FLESH-EATERS | HERB-EATERS | ALL-EATERS | FRUIT-EATERS -------------+-------------+-------------+-------------+-------------- Examples. |Cat, dog, |Cow, horse. |Hog, peccary.|Man, monkey. |lion. | | | -------------+-------------+-------------+-------------+-------------- Length of |3 times |30 times |10 times |12 times food tube. |length of |length of |length of |length of |body. |body. |body. |head-trunk. -------------+-------------+-------------+-------------+-------------- Teeth. |Pointed for |Layers of |Cutting teeth|Teeth even, |tearing |enamel and |project. |close |flesh. Canine|dentine |Canines form |together. |teeth long. |forming |tusks. |Canines not | |ridges. | |projecting. -------------+-------------+-------------+-------------+-------------- Digits. |Sharp claws. |Hoofs. |Hoofs. |Flattened | | | |nails. -------------+-------------+-------------+-------------+-------------- Colon. |Smooth. |Sacculated. |Smooth. |Sacculated. =============+=============+=============+=============+==============

_Milk_ of cows is improperly called a perfect food by some writers. Although it contains the four classes of food stuffs, the proteid is in excess, the fuel food being deficient. Buttermilk is more digestible than sweet milk. Buttermilk and sugar form a valuable food for infants. Skimmed milk still contains the proteid, the most nutritious part of the milk. Sour milk, or “clabber,” and curds pressed into “cottage cheese” are more digestible than sweet milk. _Cream_ is more easily digested than _butter_, which is a solid fat. _Cheese_ is a very concentrated proteid food, and should be eaten sparingly. _Eggs_ are a valuable food. Is there more proteid or fat in eggs? (See Table.) Pork and veal are the most indigestible of meats. _Fish_ is nearly as nutritious as meat. There used to be a supposition that fish nourished the brain because it contains phosphates; but there are more phosphates in meat than in fish, and more in grains than in meat.

_Grains_ contain considerable proteid (gluten), but they especially abound in starch. Wheat flour contains more gluten than corn meal, hence it is more sticky, and retains the bubbles of gas so that the dough rises well in bread making. Eggs are sometimes added to corn meal to make it sticky and cause it to rise well. Which grain has the largest percentage of oil? (See Table.) Of starch? Of gluten? Which is poorest in gluten? _Grains may be made to resemble fruit_ by long cooking at a high temperature (300° Fahr.), for their starch is thus changed to _dextrin_, a substance resembling sugar. You learned that the starch of fruit is turned into sugar as the sun ripens it. Dextrin is yellow and gives the dark color to toasted bread. It is changed to sugar almost instantly when brought in contact with saliva. It is used as a paste on postage stamps.

_Vegetables contain much water and woody fiber._ _White potatoes_ are underground stems and are _one fifth starch_. Yams, or sweet potatoes, resemble roots, and contain both starch and sugar. _Beans and peas are very nutritious._ They have been called “the lean meat of the vegetable kingdom.” They require boiling for several hours. If the skins are removed by pressing them through a colander, they are very easy of digestion. This _purée_ of beans makes delicious soup. “Hull-less beans” and “split peas” are also sold by grocers.

PRACTICAL QUESTIONS.--=1.= Clothing and shelter for man or beast economize what kind of food? =2.= Why should bread remain longer in the mouth than meat? =3.= In snowballing, what is the appearance of the hands when they itch from cold? Extreme cold irritates and congests the stomach more quickly than it does the hands. Why is it that ice water does not satisfy the thirst, but often produces a craving to drink more water? =4.= Should biscuits having a yellow tint or dark spots due to soda be eaten or thrown away? =5.= Why, during an epidemic, are those who have used alcohol as a beverage usually the first to be attacked? =6.= Do you buy more wood (cellulose) when you buy beans or when you buy nuts? (p. 95.) =7.= Do you buy more water when you buy bread or when you buy meat? =8.= Why do people who live in overheated rooms often have poor appetites? (p. 90.) =9.= Explain how the stomach may be weakened by the eating of predigested foods. =10.= Why are deep breathing and exercises that strengthen weak abdominal walls better for the liver than are drugs? (See p. 58.) =11.= Sixty students at the University of Missouri found by doing without supper that their power to work was greater, their health better, and many of them gained in weight. So they ate only two meals thereafter. If sixty plowboys tried the experiment, would the result probably have been the same? =12.= If a person began to eat less at each meal, or only ate one meal a day, yet gained in weight, should he agree with a friend who told him he was starving himself? Should he agree if, instead of gaining, he lost weight? =13.= Why is half-raw or soggy bread harder to digest than the raw grain itself? Which would be thoroughly chewed and cause a great flow of saliva? =14.= Ask a fat person whether he drinks much water. A lean person. =15.= Why is one whose waist measures more than his chest a bad life insurance risk? =16.= What changes in habits tend to make a rheumatic middle-aged person more youthful? =17.= How is the ingenious “fireless cooker” constructed?

=Atwater’s Experiments with Alcohol.=--A few years ago Professor Atwater proved that if alcohol is taken in small quantities, it is so completely burned in the body that not over two per cent is excreted. He inferred that it is a food, since it gives heat to the body and possibly gives energy also. His experiments did not show whether any organ was weakened or injured by its use. As alcohol is chiefly burned in the liver, it probably cannot supply energy as is the case with food burned in nerve cell and muscle cell. The heat supplied by its burning is largely lost by the rush of blood to the skin usually caused by drinking the alcohol. Dr. Beebe, unlike Professor Atwater, experimented upon persons who had never taken alcohol, and whose bodies had not had time to become trained to resist its evil effects. He found that it caused an increased excretion of nitrogen. When the body became used to it, this decreased, but the proteid excreted by the kidneys contained an abnormal amount of a harmful material called _uric acid_. Uric acid, a substance which is present in rheumatism and other diseases, is usually destroyed by the liver. As the burden of destroying the alcohol falls chiefly upon the liver, it is not surprising to find that it is so weakened and injured by alcoholic drink that it cannot fully perform its important functions. Bright’s disease and other diseases accompanied by uric acid are more frequent among persons who use alcoholic drinks.

=Definition of Food.=--_A food is anything which, after being absorbed by the body, nourishes the body without injuring it._ Does alcohol or tobacco come within this definition?

=Advantages of Good Cooking.=--Taste and flavor may be developed; parasites are killed; taste may be improved by combining foods; starch grains are burst and the food softened. Thus digestion is aided.

=Disadvantages of Bad Cooking.=--Proteid foods are hardened; flavors may be driven off; too many kinds of food may be mixed; cooked vegetables are more likely to ferment than raw vegetables; palatable food may be made tasteless or soggy or greasy; soda and other indigestible ingredients may be added; food may be so highly seasoned as to cause catarrh of the stomach; it may so stimulate the appetite that so much is eaten as to overload the stomach. Food may be made so soft that it cannot be chewed and is eaten too rapidly; for instance, bread shortened with much grease.

=The Five Modes of Cooking.=--Food may be cooked (1) by _heat radiating from glowing coals_ or a flame, as in broiling; (2) by _hot air_, as baking in a hot oven; (3) by _boiling in hot water or grease_, as frying; (4) by _hot water_, not boiling, as in stewing; (5) by _steaming_.

=Radiant Heat.=--_Toasting_ bread and _broiling_ meat are examples. The meat should be turned over every ten seconds to send its juices back and forth, thus preventing their escape, and broiling the meat in the heat of its own juices. _Roasting_ is an example of this method combined with the second method. The fire should be hot at first in order to sear the outside of the meat and prevent the escape of its juices. If the piece roasted is small, the hot fire may be kept up; but if it is large, a longer time is required, and the fire should be decreased, otherwise the outside will be scorched before the central part becomes heated. White, or Irish, potatoes roasted with their skins on best retain their flavor as well as valuable mineral salts (potash, etc.).

=Cooking by hot air= can only be used with moist foods. Baking is an example. Foods only slightly moist are made hard, dry, and unpalatable if cooked by this method.

=Cooking by Boiling.=--To boil _potatoes_ so as to make them mealy instead of soggy, the water should be boiling when they are put in, and after they are cooked the water should be poured off and the pot set on the back of the stove for the potatoes to dry. Boiling _onions_ drives off the acrid, irritating oil. Rapid boiling of vegetables gives less time for the water to dissolve out the nutrients. (See Steaming.) Raw _cabbage_ is treated by the stomach as a foreign substance, and sent promptly to the intestine; cabbage boiled with fat may remain in the stomach for five hours. Instead, it should be boiled in clear water for twenty minutes. _Beans_ and _peas_ require several hours’ boiling.

=Cooking in hot liquid below the boiling point= is better than boiling. In _frying_ meat, it should be put in hot grease that a crust may be formed to prevent the grease from soaking in. Grease much above boiling point becomes decomposed into fatty acids and other indigestible products. Hence butter is more digestible than cooked fats. In whatever way meat is cooked, it should never be salted until the cooking is finished or the salt will draw out the juices which flavor it. _Eggs_ may be cooked by placing them in boiling water and setting the kettle off the stove at once to cool. A finely minced hard-boiled egg is as digestible as a soft-boiled egg. Since boiling for more than a very few minutes coagulates and hardens albumin, there is no such thing as boiling meat without making it tough and leathery throughout. It may be stewed, a process which belongs to the next method.

In _stewing meat_, it may be plunged into boiling water for a few minutes; this coagulates the albumin on the surface. The fire should then be reduced, or the vessel set on the cooler part of the stove, or a metal plate should be placed beneath it, that the water may barely simmer. The water should show a temperature of 185° or 190° if tested with a thermometer. A piece of meat cooked in this way is tender and juicy.

=Cooking by steam= requires a double vessel or a vessel with a perforated second bottom above the water, through which the steam may rise to the food that is to be steamed. _Steamed vegetables_ have a better flavor and are more nutritious than those cooked in any other way. A steamer is different from a double boiler. _Oatmeal_ should be cooked for at least forty minutes, and it is more digestible if steamed for several hours until it is a jelly. To do this, it may be cooked during the preparation of two meals. Cooking that leaves it lumpy and sticky is a disadvantage, and makes it more likely to ferment than if eaten raw.

THOUGHT QUESTIONS. =Cooking.=--_Meat._ =1.= In making soup, why should the meat be put in while the water is cold? =2.= In roasting meat, why should the oven be hot at first, and more moderate afterward? How should you regulate the temperature in boiling or stewing meat? =3.= What happens to salt or anything salty on a cloudy, damp day? This is because the salt attracts ____. This shows that meat should not be salted until after it has been cooked, because if salted before ____. =4.= Very tough meat should be b__ed or st__ed. =5.= Meat may be prevented from becoming grease-soaked when frying by having the grease very ____, use very ____, simply greasing the ____.

=6.= _Bread._ Bread crust causes the ____ to be used more and cleans them. It will not ____ together in the stomach like the crumb. It increases the quantity of the ____, and is more digestible than the crumb, since the ____ has been changed by slow heat to ____ (p. 112). Therefore loaves or biscuit should be (large or small?) and they should (touch or be separated?) in a pan. =7.= How can you tell whether the oven has been too hot while the bread was baking? =8.= Why can you tell best about the digestibility of bread when you are slicing it? =9.= Regulating the heat is the greatest art of the cook. How may the temperature of the oven be lowered by means of the damper? The draft? The fuel?

EXERCISES IN WRITING.--Story of a Savage who went to dwell in a City (his trouble with artificial ways). Is it easier to learn Physiology or to practice it? How to make Bread. Describe People seen in an Audience (tell what their appearance suggests). A Scene at a Dinner Table. Thoughts of a Physician on his Round of Visits. A Good Cook. A Bad Cook. Is Cooking a Greater Accomplishment than Piano Playing? Common Causes of Illness. The Influence of Imperfect Digestion upon the Other Organs. Effect of Lack of Muscular Activity. The Way of the Transgressor is Hard. What Fools we Mortals be! Health Fads. Temperance in all Things. The Right Way the Easiest. Looking Back. Looking Forward. Hygiene of the Schoolroom. Patent Medicines. Microbes. Mind Cure. Nervous Women. Dissipated Men. How a Friend of mine lost his Health. Why a Friend of mine is Sound and Strong. Tobacco. It never pays to neglect the Health. Which does more Harm, an Ignorant Cook or an Ignorant Janitor? A Visit to a Sick Room. Alcohol and Crime. Natural Instincts and Appetites; how preserved, how lost. A Lesson about Alcohol based upon the Morning News. Effects of Alcohol upon the Greatness of our Country (workmen, voters, soldiers, children). Adam’s Apothecary Shop. Adam’s Ale (water).