about one fifth oxygen and four fifths nitrogen. This nitrogen is of
no use to the body, and is exhaled unchanged. _A part of the oxygen
inspired is taken up by the blood, and carbon dioxid is sent out in its
place._ About half a pint of water is given off through the lungs in a
day. Minute quantities of injurious animal matter are also given off
in the breath from even the soundest person. The air leaves the lungs
warmer, damper, and with more carbon dioxid than when it entered (Exps.
3 to 9).
[Illustration: FIG. 80.--VENTILATION OF STOVE-HEATED ROOM.[5]
How are the inlet and outlet situated with reference to the stove?]
[5] From Coleman’s Elements of Physiology (400 pp.). The Macmillan
Co., N.Y.
Persons with decayed teeth, catarrh, indigestion, diseased lungs,
or other unsoundness give off still more of this material. When
many people are assembled in a badly ventilated room, the amount of
injurious animal matter in the air is much increased, and is called
“_crowd poison_.” Its odor is strong and repulsive to one who just
enters the room, but the sense of smell becomes dull to it in a few
minutes. It would seem that nature gives a fair warning against harm;
but if we disregard the warning it soon ceases.
=People who are really Unclean.=--Nature’s plan seems to be for us
to live out of doors. Air once breathed is impure. It is just as
unfit to enter our bodies as muddy water or decayed food. Yet many
who call themselves cleanly and refined, and _will not allow a speck
of dirt to remain on their clothes, nor use a spoon just used by
another, do not object to breathing into their lungs, over and over
again, the cast-off air from the lungs of others_. If a window is
opened for ventilation, they are horror-stricken for fear of drafts.
Drafts are injurious only to persons perspiring, or to those who have
coddled the skin by continually overheating it. There are thousands
of schools, churches, and theaters all over the land which reek daily
with the malodorous particles from the lungs of their occupants.
Although the air in them is odorless to those who occupy them, it is
disgusting to any one who enters from the fresh air. Figure 80 shows
the correct ventilation of a stove-heated schoolroom.
=Dust= causes catarrh of the bronchial tubes and chronic inflammation
of the lungs; it prepares for consumption, by gradually weakening
the lungs of those who breathe it. Intelligence and common sense are
necessary to prevent it from accumulating in the house. The chief
purpose of the house cleaning should be not only to remove bits of
paper from the floor, which do no harm even to the shoes, but _to
remove impurities from the air_. _It does no good to stir up the dust
and allow it to settle down again_ (Exp. 12). In many houses dust is
thus allowed to accumulate for months. Experiments show that dust and
germs floating in the air are not diminished to a great extent by a
gentle draft through the room. The windows must be open and sweeping
done in the direction of the air currents; the windows should be _left
open for a long while after the sweeping_. A windy day is best for
sweeping.
The habit some housekeepers have of buying furnishings and
bric-à-brac for the home until it looks like a retail store or
junk shop, makes it almost impossible to clean their houses. A few
articles, carefully selected, adorn a home more than many bought
at random, and they do not litter the house and serve as traps for
dust. With all precautions some dust may settle down. This should not
simply be stirred up again with a feather duster, but _the dusting
should be done with a damp cloth_. Ashes should be sprinkled before
they are moved. Carpet sweepers, but never brooms, should be used
upon carpets. Carpets and lace curtains are truly dust traps, in
which dust will accumulate without limit. Those who value the health
will not use such uncleanly abominations, at least in bedrooms.
Though linoleum, bare floors with movable rugs, oiled and painted
floors, may not look so comfortable as a fixed carpet, they bring
far more comfort in the end. _The weakening effect of ordinary dust
is one of the chief causes of lung diseases_, and prepares a fertile
soil for the consumptive germ. The sputum coughed up by consumptives
falls upon the floor or street, soon dries, and the germs are driven
about by the wind. In many cities there is a law against spitting in
public places, and the streets are flushed with water before they are
swept.
[Illustration: FIG. 81.--The air enters through a special inlet and is
warmed as it passes through hood surrounding the stove.]
[Illustration: FIG. 82.--Chimney with a passage behind fireplace, or
grate, in which the air is warmed as it enters.]
=Ventilation= presents no difficulties in the summer time or in warm
climates. The reason that it is a difficult question in cold weather
is because the air furnished must be not only pure, but warm. To keep
cold air out often means to keep foul air in. _Heating with hot air_,
by which system pure air is passed over a furnace, and fresh air
constantly admitted, may be a good method (Figs. 80, 81), but is often
a dismal failure because it dries out the air, which in turn dries out
the skin. To prevent this, wide vessels of water should be set at the
inlets. Dry air is cooling. Why? Dr. Barnes proved that moist air at
65° is as comfortable as dry air at 71°. Air saturated with vapor at
60° will _only be 50 per cent saturated at 80°_. Such air dries out
the mucous membrane of eyes, nose, and throat. Heating by _hot water_
circulating in pipes, or _by steam_, gives no means of introducing
fresh air, and is likely to cause worse ventilation than any other
method. The radiators should stand close to windows or other fresh-air
inlet, that the air may be heated as it enters, and the outlet for air
should be farthest from the radiators. The same rules apply to heating
by _stoves_. An oil stove for heating is an inconceivable iniquity to
any but a person densely ignorant of hygiene. Heating by _fireplaces_
(Fig. 82) is the most healthful of all methods, for there is a constant
removal of air through the chimney, and this air will be replaced;
even if all doors and windows are closed, it will come in through tiny
cracks. _Radiant heat_ travels in straight lines from a fireplace
and _warms solid objects_, but not the air passed through. Hence an
open fire will keep the body warm with the room at a low temperature.
Fireplaces, however, do not afford sufficient heat in severe climates.
_Stoves_ are not as healthful as fireplaces, for there is not so
much air removed through the pipe as through the chimney. _Carbon
monoxid_, unlike carbon dioxid, is an _active_ poison causing the blood
corpuscles to shrivel. It passes through red-hot iron or a cracked
stove or furnace.
[Illustration: FIG. 83.--BLACKBOARD SKETCH.]
[Illustration: FIG. 84.--Facial expression in mouth breathing, and
breathing through the nose.]
=Reasons for Breathing through the Nose= (Fig. 83).--(1) The many
blood vessels in the mucous membrane lining the nasal passages so
_heat the air_ that it does not irritate the bronchial tubes. (2)
_The hairs in the nostrils strain the air_ and catch dust; the cilia
of the nasal passages also do this. (3) A mouth-breather often
_swallows food before chewing it sufficiently_, because he cannot
hold his breath longer. (4) The nasal mucous membrane of an habitual
mouth-breather _dries and shrinks_ and obstructs the circulation,
bringing on _catarrh of the nose_. (5) Mouth breathing causes an
_unpleasant expression of countenance_ (see Fig. 84). (6) The breath
does not come through the nose as quickly as through the mouth; the
_lungs are kept more expanded_, and one does not get “out of breath”
so quickly. (7) _The voice of the mouth breather has a hard twang_,
not a full, resonant tone as when the nostrils are open. (8) _Flavors
and odors_ are better appreciated. Sometimes the sense of smell
is almost lost by mouth breathers. If one cannot breathe through
the nose, even for a short time, there is probably an adenoid, or
tonsil-like, growth in nose or pharynx, and a physician should be
consulted. “Adenoids” are glandular or grapelike in form.
=Diseases of the Respiratory Organs.=--_A cold or catarrh is an
inflammation of a mucous membrane._ If the inflammation is in the
nasal passages, it is called a _cold_ in the head; if it is in the
pharynx, it is called a _sore throat_; if it is in the larynx or
voice box, there is _hoarseness_; if it is in the bronchial tubes,
it is _bronchitis_; finally, if it is in the air cells, it is
_pneumonia_. If the air is cut off from access to the air cells,
there is an attack of the painful disease called _asthma_, which is
accompanied by a feeling of suffocation. Some believe that asthma
is caused by the mucous membrane lining the finest bronchial tubes
becoming inflamed and swollen, and closing the tubes; others think
that the muscles in the large bronchial tubes contract and close the
tubes. _Pleurisy_ is inflammation of the pleura and makes breathing
painful. If much fluid forms between the pleuras, the inner pleura
may press upon the lungs and interfere with breathing.
=Alcohol= not only weakens the blood vessels near the surface, but the
blood vessels in general. Weakened and congested blood vessels in the
lungs make them more liable to pneumonia and other congestive diseases.
Continual congestion causes an abnormal growth of connective tissue
fiber in the walls of the cells. This diminishes the capacity of the
lungs and interferes with the exchange of carbon dioxid and oxygen.
=Tobacco.=--It is often asked why cigarettes are so much more injurious
to the health than pipes and cigars. The nature of the paper of
cigarettes and various other absurd reasons have been assigned. The
true reason is that the cigarette smoker usually _inhales_ the tobacco
smoke. Cigar smoke, if drawn into the lungs, would usually be coughed
up at once. Cigarette smoke is weaker--it is so weak that the smoker is
not content simply to absorb the nicotine through the mucous membrane
of the mouth; he draws it into the lungs. The very mildness of the
smoke leads to inhalation. Hence, as the _surface_ of the lungs is a
_hundred times greater_ than the surface of the mouth, and _its lining
much thinner_, cigarette smoking is far more injurious than cigar
smoking.
The poison accumulates in the bowl of a pipe; hence an old pipe is
very injurious. The irritation of tobacco smoke often sets up a
chronic dry catarrh of the air passages; rarely it causes cancer of
lips or tongue. Sir Henry Thompson says: “The only persons who enjoy
smoking and find it tranquillizing at times are those who smoke in
great moderation. Men who are rarely seen without a cigar between
the lips, have long ceased to enjoy smoking. They are confirmed in a
habit, and are merely miserable when the cigar is absent.” They do
not smoke for pleasure, but to escape misery which wiser men escape
by avoiding tobacco altogether.
[Illustration: FIG. 85.
FIG. 86.
FIG. 85.--FLATTENED CHEST and waist organs sunken from wearing tight
clothing since the age of fourteen. Such women often walk with bodies
bent forward to hide the prominent abdomen.
FIG. 86.--A NATURAL WOMAN.]
PRACTICAL QUESTIONS.--=1.= State how in the case of a person with
round shoulders a gradual remolding of cartilages (which ones?),
the strengthening of the muscles (which ones?), and the practice of
deep breathing may each contribute toward acquiring an erect and
perfect figure. =2.= Should a hat be well ventilated? (A punch for
making the holes costs a dime.) Should a hat be stiff or soft? =3.=
Name habits that impair the power of the lungs. =4.= How could you
convince a person that a bedroom should be open while and after it
is swept? That it should be ventilated at night? =5.= Which is the
more injurious to others, tobacco chewing which causes the ground
to be unclean, or smoking which renders the air impure? =6=. Why do
those who stand straight up to hoe not get tired half so quickly as
those who bend or “hump” over? (Chap. VI.) =7.= Why do students who
sit in rocking chairs, or from other causes lean the head forward
when they study, often find that they recover from drowsiness if they
sit erect, or sit in a straight chair? =8.= How are high collars a
fruitful source of bad colds? =9.= If the draft up the chimney of
the fireplace, when the fire is burning, takes up a volume of air
sufficient for many people, why is it unnecessary to open a window?
=10.= Why does cold impure air make a person colder than cold pure
air? (p. 14.) =11.= Do the modern customs of uniformity in dress for
all classes and climates, shipping foods from great distances, one
section or nation imitating the ways of another section or nation,
lead toward health or disease? Do such customs violate or conform
to the great biological law that life is a process of adaptation to
environment?
[Illustration: FIG. 87.--SUSPENDERS should have a pulley or lever at
the back, that the strap on one side may loosen when one shoulder is
raised.]
[Illustration: COLORED FIGURE 6.--ORGANS OF THE TRUNK.
_cb_, collar bone; _r_, ribs; _z_, tongue bone (hyoid); _k_, _k_,
cartilages of larynx; _l_, windpipe; _s_, thyroid gland; _rv_, right
ventricle; _lv_, left ventricle; _ru_, right auricle; _lu_, left
auricle; _a_, aorta; _ka_, artery to head (carotid); _sa_, subclavian
artery; _la_, pulmonary artery; _oh_, superior vena cava; _hv_, jugular
vein; _lu_, lungs; _f_, diaphragm; _lb_, liver; _g_, gall bladder;
_s_, stomach; _x_, spleen; _n_, mesentery with vessels; _d_, small
intestine; _gd_, large intestine; _b_, cæcum; _w_, vermiform appendix;
_h_, bladder.]
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).
CHAPTER VIII
THE NERVOUS SYSTEM
=Review Questions introducing this Subject.=--What is a cell? What
are the five supporting tissues? What are the two master tissues? Why
are they so called? What kind of cells have many branches? Does the
food ever come in contact with the salivary glands? When you look
at a basket of apples, the sight “makes your mouth water.” Is there
a connection between the eye and the mouth? What two tissues enable
the skin to blanch and to blush? Do the different organs share the
blood in the same proportions at all times? How can this proportion
be changed? How is the brain protected from injury? How is the spinal
cord protected? Is the hole for the spinal cord through the main body
of the vertebra, or behind the main body?
=Harmonious Activity.=--Strike suddenly at the eye of another, and the
lids fall to protect it, and the hands rise to ward off the blow. If
a grain of dust gets into the eye, the tear glands form tears to wash
it out. If you touch the hand unexpectedly to a hot iron, the muscles
of the arm jerk the hand away. If the foot of a sleeping person is
tickled, the muscles of the leg pull it away. Many muscles coöperate
in the act of running. If the human being were merely an assemblage of
working organs, the organs might act independently, and there would be
such confusion that the body would be powerless, and life could not be
maintained. The nervous system enables the organs to work together for
the common good. Why does an ameba not need a nervous system?
=The Need of Nerve Centers as well as Nerves.=--If there were no
central office in a telephone system of one thousand subscribers, then
every subscriber, in order to communicate with every other subscriber,
would need one thousand wires running into his house; all together,
there would have to be several hundred thousand (to be exact, 499,500)
wires. With a central office only one thousand are needed. As a
telephone system has central offices, so the nervous system has nerve
centers. Nerve centers contain nerve cells. Although there are some
subordinate nerve centers in the spinal cord, the greatest collection
of nerve centers in our bodies is in the skull, and is called the
_brain_. Fishes were the lowest animals studied in animal biology found
to possess a true brain.
The nervous system, unlike a telephone system, has other duties
besides allowing _communication_. It enables us to _think_, and, after
reflection, to _will_ and to _act_ by controlling the various organs.
[Illustration: FIG. 103.--Showing a NEURON, _A_, or nerve cell with all
its parts--dendrites, cell body, and axon; _B_, a portion of a white
fiber highly magnified. (Jegi.)]
=The Units of which the Nervous System is Constructed.=--A nerve cell
with all its branches, or fibers, is called a _neuron_ (see Fig. 103);
some neuron branches are several feet long. Neurons are the units
that compose the nervous system. The living substance in cells is
called _protoplasm_. The protoplasm in nerve cells possesses the most
marvelous and varied powers of any known substance, for the nerve cells
are the seat of the mind.
[Illustration: FIG. 104.--LARGE NERVE TRUNK, such as supplies the
muscles. Cross-section (magnified 6 diameters), showing bundles of
nerve fibers. (Peabody.)]
=Nerve Cells and Fibers.=--The many branches of nerve cells make them
the most remarkable of all cells for irregularity in shape. Since
_the protoplasm of the cell continues into the fibers_, it is plainly
wrong to consider the nerve cell as something apart from its fibers.
It is not a complete cell without them. A cell usually has many
short branches called _dendrons_ or _dendrites_ (see Fig. 103) for
communicating with near-by cells, and one long branch called an _axōn_
(Fig. 103) for communicating with distant parts. The axons form the
fibers that go to the skin, muscles, and other organs.
=A Nerve.=--These long branches, or axons, of nerve cells go all
over the body and are often bound together into visible cords called
_nerves_, or nerve trunks (Fig. 104).
[Illustration: FIG. 105.--_c_, a white fiber with its fatty sheath
(dark); _d_, two gray fibers (without sheath).]
=White and Gray Fibers= (Fig. 105).--Some fibers have a _fatty
covering_ surrounding the _thread of protoplasm_; they are white and
glistening, and are called _white fibers_. Others are without this
fatty covering, and are called _gray fibers_. Both kinds of fibers have
_connective tissue_ on the outside to strengthen them. If we let a lead
pencil represent a white fiber, the lead corresponds to the axis of
protoplasm; the wood corresponds to the white, shiny fat that surrounds
it; and the varnish corresponds to connective tissue on the surface of
the fiber. A number of white fibers together makes a white mass that
is called _white matter_. The axis of a white fiber, of course, is not
white. A mass of cells or of gray fibers is called _gray matter_. The
oxidation of the gray matter, or protoplasm, in neurons gives rise to
nerve energy.
=Feeling Cells and Working Cells.=--Nerve cells are divided into two
classes: _sensory cells_, which feel or receive impressions; and _motor
cells_, which send out impressions to the working organs. Those fibers
which carry impressions to the receiving cells are called _sensory
fibers_; those which carry impulses from the cells to the working
organs are called _motor fibers_.
=Ganglia and Nerve Centers.=--Nerve cells are not scattered uniformly
in nervous tissue, but are gathered into groups. A group of nerve
cells is called a _ganglion_ (Fig. 106). One or more ganglia having a
single function, such as to control the muscles of breathing, form what
is called a _nerve center_. The brain consists of a number of nerve
centers with their connecting fibers.
[Illustration: FIG. 106.--A GANGLION.]
[Illustration: FIG. 107.--CROSS-SECTION OF SPINAL CORD, showing area of
gray matter (dark).]
=Gross Structure of the Spinal Cord.=--The nerve fibers from nearly
all over the body lead to cells situated in a large cord in the spinal
column called the _spinal cord_. The spinal cord is _separated by a
deep fissure almost into halves_ (Fig. 107). The cells are situated in
the central portion of each half, and the _two masses of gray matter_
thus formed are connected by a narrow isthmus of gray matter. The outer
part of the cord consists chiefly of white fibers. The _white matter
is thus on the outside of the cord_ (Fig. 107). The brain, unlike the
cord, has the gray matter on the outside and the white matter on the
inside. For microscopic study of the spinal cord, see Fig. 108.
=The Work of the Spinal Cord.=--There are two functions of the cord:
reflex action and transmission of impulses from the body to the brain.
Reflex action is action that takes place without the aid of the will.
[Illustration: FIG. 108.--SECTION OF SPINAL CORD, showing nerve cells
(large black spots) with their branches (black dots and lines). Five
bundles of nerve fibers are shown near upper margin. (Peabody.)]
=Reflex action= never begins in the cord, but at the outer end of a
sensory fiber, usually located in the _skin_. The impression goes to
the cord along a _sensory fiber_. It is received in a _sensory cell_
and transferred by dendrons to a _motor cell_ which sends back an
impulse along a _motor fiber_ to a _muscle_; the muscle contracts and
the action is complete. At least two nerve cells are necessary for
reflex action. The actions of the lowest animals are almost entirely
reflex.
=Reflex Action, Consciousness, and Will.=--Usually not all of the
force of the impulse is transferred to the motor cell. The sensory
cell by means of another of its many branches may _transfer part of
the impulse to a cell which sends it to the brain_. Hence a reflex act
is not necessarily an unconscious one. If you unintentionally touch
the hand to a hot stove pipe, you may be conscious of the pain and the
involuntary jerking away of the hand at the same time.
=Reflex Action and the Will.=--The will may _inhibit_, or prevent, an
expected reflex act. Yet many reflex acts occur in spite of the effort
of the will to prevent them. One cannot always keep from closing the
eyes before a threatened blow even if from the other side of a plate
glass window, and it is known there is no danger. Sneezing is a reflex
act and cannot always be prevented. The forming of saliva and other
secretions are reflex acts. _Reflex acts are quicker than voluntary
acts._ An eighth of a second is about the time required for a person to
press an electric button after seeing a signal; a reflex act may occur
in a shorter time.
[Illustration: FIG. 109.--BRAIN AND SPINAL CORD.]
=The Brain consists of Three Chief Parts.=--(1) There is an enlargement
at the top of the spinal cord called the _medulla_, or the medulla
oblongata. It may be regarded as the part of the spinal cord within
the skull (see Figs. 109, 110, 114). (2) Above the medulla is the
_cerebellum_, or little brain. (3) The _cerebrum_, or large brain,
fills all the skull except the small part occupied by the medulla and
cerebellum. The cerebrum covers the cerebellum. (Fig. 110.) Is this
true of the monkey’s brain? (See Fig. 113.)
=The work of the medulla= is chiefly to control the vital functions
(see Figs. 110, 114). Here are located the centers for regulating the
_breathing_, the _heart beat_, the _size of the blood vessels_ (thus
regulating nutrition), and also the less important centers that control
_swallowing_, _secretion of saliva_, and _vomiting_. The center for
breathing is sometimes called the _vital knot_, because although the
cerebrum and cerebellum may be removed from an animal without causing
immediate death, the slightest injury to the vital knot kills the
animal at once. In cases of hanging, death is caused by injury to this
center.
[Illustration: FIG. 110.--THE BRAIN (cerebrum, cerebellum, medulla).]
[Illustration: FIG. 111.--ASSOCIATION FIBERS, connecting cells within
the cerebrum. (Jegi.)]
=Automatic Action.=--The center called the vital knot is said to
regulate the breathing automatically, not reflexly. Reflex acts start
in the skin; _automatic acts start in the interior of the body_. _The
condition of the blood regulates the breathing_ automatically during
sleep, and partly regulates it during waking. If too much carbon dioxid
accumulates in the blood this excites the vital knot, which sends out
stronger impulses to the respiratory muscles. Deeper breathing follows,
which purifies the blood, and the breathing is then shallow or slow
until carbon dioxid accumulates again.
=The Four Kinds of Nerve Action and the Centers that control
them.=--The _cord_ controls chiefly _reflex_ action; the _medulla_
controls chiefly _automatic_ action; the _cerebellum_ controls chiefly
_coördinate_, or harmonizing, action; the _cerebrum_ controls the
purely _voluntary_ acts, for it is the seat of _consciousness_ and
_thought_. The medulla, like the cord, has the gray matter on the
inside (Fig. 109).
[Illustration: FIG. 112.--SENSORY AND MOTOR FIBERS. (Jegi.)]
=Structure of the Cerebellum.=--The cerebellum, like the cerebrum, has
the gray matter or cells on the outside. The gray matter is folded into
furrows that are not nearly so winding as the folds in the cerebrum
(see Fig. 115). The fibers going to the surface cells have a branched
arrangement called the _arbor vitæ_, or tree of life, which is shown
where the cerebellum is cut. The cerebellum, like the cerebrum, is
deeply cleft and thus divided into halves, called _hemispheres_,
connected by a band of white matter.
[Illustration: FIG. 113.--BRAIN OF A MONKEY. Numerals show location of
motor centers. (See Fig. 115.)]
[Illustration: FIG. 114.--THE LOBES OF THE RIGHT SIDE OF BRAIN and
their functions. (Jegi.)
The speech center is true only for left-handed persons. Medulla is
marked “Bulb.”]
=The work of the cerebellum= is to aid the cerebrum in controlling the
muscles. _It coördinates the muscular movements_; that is, it makes the
muscles act at the right time and with due force in complex acts, such
as standing, walking, talking. A man could strike just as hard without
the action of the cerebellum, but he would not be likely to hit what he
aimed at. A drunken man staggers and fails to control the muscles in
walking because the alcohol has caused the blood to collect and congest
around the cerebellum and press upon it. One whose cerebellum has been
injured by accident staggers like a drunken man.
[Illustration: FIG. 115.--MOTOR AND SENSORY AREAS OF LEFT HEMISPHERE.
Speech center marked “Lips.”
In what region are the motor centers? The sensory centers?]
=Coverings of the Brain.=--Lining the skull and covering the cerebrum
are found _two membranes_ which inclose a lymph-like fluid. Thus a kind
of _water bed_ is made which surrounds the soft and delicate cerebrum
and protects it from jars. A membraneous net, or meshwork, of blood
vessels covers the cerebrum and plentifully supplies it with blood.
=Structure of the Cerebrum.=--The gray matter, or cell mass of the
cerebrum, forms a surface layer, called the _cortex_ (“bark”), about
one eighth of an inch thick. This _gray layer is deeply folded_, the
folds, or _convolutions_, being separated by deep furrows, some of
them an inch deep (see Fig. 110). Thus the area of the surface layer
is increased to several times what it would be if smooth. Intelligence
increases with increase in the number and depth of the convolutions.
The greater part of the cerebrum is white matter. This consists largely
of associational _fibers_ (Fig. 111) _which connect the cells in the
gray matter with each other_ and with important interior ganglia at the
base of the cerebrum (Fig. 112). These basal ganglia are the largest
parts of the brains of the lower vertebrates (Animal Biology, Figs.
222, 259). Why do these animals not need large cerebrums? The human
cerebrum comprises nearly seven eighths of the weight of the brain. A
deep fissure divides it into the right and left cerebral hemispheres. A
band of white matter connects the hemispheres.
=Functions of the Cerebrum.=--The cerebrum is the seat of
_consciousness_ and thought, and of all activity controlled by the
_will_. It also _directs the work of the lower nerve centers_ in the
spinal cord, medulla, and cerebellum.
It receives sensory messages from all parts of the skin and through
the special senses. It sends out motor messages to all the voluntary
muscles, and more indirectly to the involuntary muscles. The cerebral
fibers are of three kinds: _sensory_, _associational_ (connecting cells
in cerebrum), and _motor_ (Figs. 111, 112). It is estimated that the
cerebrum alone contains 9,200,000,000 cells.
=Spinal and Cranial Nerves.=--The nerves from the spinal cord go out
through notches between the vertebræ. Since there are _thirty-one
pairs_ of _spinal nerves_ (Fig. 109) and only twenty-four vertebræ,
some of the nerves go out through holes in the sacrum. The _cranial
nerves_ (to eyes, ears, tongue, nose, face, etc.) leave the brain
through holes in the cranium, or skull. There are _twelve pairs_ of
them.
=Relation of the Cerebrum to the Lower Centers.=--As already stated,
nerve activities are of four kinds,--reflex, automatic, coördinate,
and voluntary. A manufactory has more complex work than a shop. A
man with a shop may enlarge it into a factory and leave trained
assistants in charge of the different shops, keeping only the general
management for himself. If he should cease to control his assistants
entirely, the work of the factory would soon be in disorder. If the
manager should try to direct everything, he would become exhausted.
So the cerebrum, the seat of the will and the reason, leaves the
reflex centers in the spinal cord, medulla, and cerebellum to do most
of the work. If the mind wishes the hand to move and grasp the hand
of a friend, the motor center in the cerebrum sends a message to the
cerebellum; and if the cerebellum has been well trained, the act is
accurately performed.
=A less imperfect wisdom than that of the mind= is in the lower nerve
centers. The reason and will control the lower centers through the
cerebrum, but the control is very limited. It is well that this is
so, not only for the relief of the cerebrum, but for the safety of
the body. Can you change the rate of the heart beat by the exercise
of the will? Can you blush at will, or prevent the flushing of the
capillaries when you are embarrassed, or when you go close to a hot
fire? It is impossible for a person to commit suicide by holding the
breath. What change in the blood would soon force a breath to be
taken? Repeat the two examples of reflex action triumphing over the
will which have already been given. We shall next take up a system of
nerves almost independent of the will.
=The ganglionic or sympathetic= portion of the nervous system controls
the viscera (_vis′sē-ra_), or internal organs, _e.g._ peristalsis of
food tube, tone of arteries. The nerves that go to the viscera branch
off from the spinal nerves not far from the spinal column, and enter a
row of ganglia on each side of the spine (see Fig. 115). Each ganglion
is connected by nerves with the one above and below it, so that they
appear like two knotted cords suspended one on each side of the spinal
column and tied together below; for both chains of ganglia end in the
same ganglion in the pelvis. Some of the fibers from the spinal cord
pass through these ganglia on their way to the viscera, losing their
white sheaths in the ganglia and emerging as gray fibers. The spinal
cord and brain with the fibers which do not pass through the double
chain of ganglia are called the _cerebro-spinal system_. The double
chain of ganglia and the fibers which go through them are called the
_ganglionic_ or _sympathetic_ system.
[Illustration: FIG. 116.--DIAGRAM OF SYMPATHETIC SYSTEM showing double
chain of ganglia; also plexus at heart and solar plexus.]
=Why these Nerves are called the Sympathetic System.=--These nerves,
after leaving the double chain of ganglia, form many intricate networks
of ganglia and fibers. Each network is called a _plexus_ (Fig. 116).
The largest of the plexuses is just back of the stomach, and is called
the _solar plexus_. A blow upon the stomach may paralyze this plexus
and cause sudden death. _The plexuses and fibers connect the viscera
so perfectly that one organ cannot suffer without the others changing
their activity, or sympathizing with it._ An overloaded stomach causes
the heart to beat faster and send it more blood; a loss of appetite
usually accompanies illness and allows the stomach to rest. This
sympathy is necessary, for if one organ is diseased, the others do not
continue to work and tax the strength of the ailing organ.
=How the Sympathetic and Cerebro-spinal Nerves Differ.=--The ganglionic
nerves (1) contain mostly _gray fibers_; (2) pass _through ganglia_
after leaving the spinal cord; (3) control the _unconscious_ activities
of the body; (4) pass to organs which contain slow-acting _involuntary
muscles_, not to sense organs and quick-acting voluntary muscles;
(5) transmit impulses _slowly_ (about 20 ft. instead of 100 ft. per
second). Crawfish and insects have hardly more than the ganglionic
system of nerves (Animal Biology, Figs. 92, 132, 197).
=Examples of the Supervisory Functions of the Sympathetic
System.=--Regulation of the heart beat and of the size of the blood
vessels; secretion of sweat glands; contraction of pupils of eyes in a
bright light; peristalsis.
=Examples of Sympathetic Nerve Impulses reaching Consciousness.=--Pain
in colic and cramps; “heartburn” (pain in stomach from indigestion);
backache (from nerves in organs prolapsed by tight clothing pulling
upon their attachments at spine); hunger; thirst.
=The Mind and Health.=--A contented or peaceful mind is indispensable
to soundest health. Worry causes difficult breathing with bated
breath. Happiness brings full, easy breathing. Biological study of
physiology shows the futility of making health a care or anxiety,
and teaches “no meddling” with the body, whether by stimulating
it, drugging it, deforming it, overheating it, half smothering it
in close rooms, cultivating artificial instincts, etc. If the body
degenerates through wrong living, and disease ensues, a new way of
living is needed, not some quick and wonderful remedy. The new life
will renew the body and nothing else can.
HYGIENE OF THE NERVOUS SYSTEM
=Necessity of Food, Fresh Air, and Rest for Sound Nerves.=--The
health of the nerves depends upon a free supply of pure, nutritious
blood. Nearly one fifth of the blood goes to the brain. It is clear
that the brain cannot give out energy until it has first received it;
the blood supplies energy to the brain. The blood in turn receives
the nourishment from food and pure air. A rested cell is full of
nourishment; a tired cell is shriveled (see Fig. 117).
[Illustration: FIG. 117.--EFFECTS OF FATIGUE ON NERVE CELLS.
_A_, resting cell, _B_, fatigued cell, with its body and nucleus
shrunken.]
=Sleep.=--During waking hours energy is used up faster than it is
stored in the cells, and protoplasm is oxidized faster than the cells
can replace it. During sleep the opposite is true; repair is more rapid
than waste. During sleep the muscles are strengthened, the breathing is
less, the heart beats more slowly, less heat is produced, digestion is
slower, less blood goes to the brain. Why is it necessary to be more
warmly protected by clothing or bed covering when asleep than when
awake? Above all, the nervous system has an opportunity to recuperate
from the constant activity of waking hours. The eye and the ear are
rested by darkness and silence. Sleep caused by morphine or other drug
is not normal sleep and brings little refreshment.
=Practical Suggestions.=--Sleep is deepest during the second hour
after going to sleep, and a greater shock is given to the nervous
system by waking a sleeper during that hour than at another time. An
alarm clock is a very unhealthful device. One who cannot trust to
nature even to awaken has great presumption. If one does not rise
promptly upon waking naturally, the instinct to awake when enough
sleep has been taken will be lost, and the habit of sleeping too much
will be formed, and the brain, like the muscles, will become weak
from inactivity. Infants sleep most of the time, and it is injurious
to them to be waked. Adults usually require about eight hours of
sleep. There is a risk in going to sleep in a warm room, for the
bed covering which is comfortable then may not be enough to prevent
taking cold when the fire goes out. Sleep usually comes more promptly
to one who goes to bed at the same hour each night. The muscles are
relaxed in sleep, and relaxing them perfectly upon lying down and
breathing slowly, tends to bring sleep. One who is sleepless usually
finds that he is breathing fast and is holding the head stiff on
the shoulders, the teeth clenched, and the muscles contracted, even
though he is lying down. Excitement and worry during the day, but
especially just before retiring, tend to produce sleeplessness. One
who overworks his mind by too great attention to business is inviting
ruin. A student who loses sleep while preparing for an examination
will probably fail. Rested brain cells and pure blood are needed for
good work.
=Rules for Preventing Sleepiness.=--(1) Do not sit close to stove or
especially a fireplace or in very warm room, and do not wear very
warm clothing in the house. (2) Let in fresh air freely. (3) Do not
sit in rocking chair nor with chest flattened. (4) Make the last meal
a very light one.
=Habits.=--Our habits of doing and thinking and feeling really
constitute our characters. This shows the importance of right habits.
By gradually changing our habits we can strengthen our characters and
form them somewhat as we wish. When a muscle contracts in a certain
way, this act makes it easier for the muscle to contract in that way
the next time; thus great muscular strength may be developed. _When
a nerve cell acts, the circulation around the cell is increased, the
fibers develop by use, and the act is easier the next time._ We cannot
entirely get rid of our habits, because we cannot get rid of our brains.
=Healthy fatigue= is caused by the accumulation of waste products
resulting from the oxidation of substances in nerve, muscle, and gland
cells. The presence of waste in the tissues affects the nerves. We
are rested and strong when these wastes are removed and the tissues
are supplied with fresh food and oxygen. Work causes the accumulation
of _carbon dioxid, which is nature’s narcotic_.[9] The drowsy feeling
that ensues is more pleasant than the drowsy feeling from alcohol or
opium. Those who do not employ nature’s narcotic but free themselves of
it by hurried, anxious breathing become restless and crave artificial
narcotics.
[9] It has been found that it is injurious to rebreathe expired air
containing one per cent of carbon dioxid, but a far greater
percentage is harmless if introduced into fresh air, thus indicating
that the injury from poor ventilation comes chiefly from the “crowd
poison,” or organic particles thrown off.
=Fatigue without work= occurs with people who are idle. The
oxidation in their cells is not complete, and poisonous products
of the incomplete burning result. This is known as self-poisoning
(auto-toxemia). The poisons are taken by the blood to the nerves and
brain, and give a tired feeling as effectually as does hard work; or
the food may ferment in the food tube and form poisons which increase
the tired feeling. Such persons are usually irritable, while persons
who are fatigued by useful labor are likely to be dull and drowsy.
[Illustration: FIG. 118.--THE SITUATION OF HEADACHES with reference to
their causes.]
=Headaches= are caused by poisons in the blood or by pressure of
blood congested in the head. Like all other pains they should be a
source of benefit in that they show us ways of living to be shunned
in the future. Many persons, however, not only derive no profit from
a headache, but by unwise efforts to cure the pain, bring permanent
injury to themselves in addition to the suffering of the headache.
_Bromides_, _opium_, and other _poisons_ deaden and weaken the nervous
system while preventing the headache from being felt. _Headache
powders_, phenacetin, acetanelid, antikamnia, and other vile poisons
made from coal tar, shock and weaken the heart and reduce the vital
activities so that the headache is no longer felt. In consequence of
shocks from repeated doses of such drugs, the heart will not work so
well, and may give way some time in the future when an effort or strain
makes unusual demands upon it. Their use has made heart disease more
prevalent. The liver and kidney cells and the white corpuscles have to
destroy and remove the drugs. Many people are foolish enough to injure
their bodies and risk death rather than suffer pain or avoid pain by
prudent living.
_Sick headaches are foretold_ by a dull feeling, sleepiness after
eating, a coated tongue, and constipation. It would be better to remove
the undigested, spoiled food from the stomach (four glasses of water
will cause vomiting) than to take a drug. At the first indication of
trouble, abstain from eating, or use a fruit diet for twenty-four
hours, and drink water freely. This will enable the body to dispose of
the excess of waste matter.
=The Highest Living Medical Authority on Drugs.=--Dr. Osler, formerly
of Johns Hopkins University and now of Oxford University, says:
“But the new school does not feel itself under obligation to give
any medicines whatever, while a generation ago not only could few
physicians have held their practice unless they did, but few would
have thought it safe or scientific. Of course there are still many
cases where the patient or the patient’s friends must be humored
by administering medicine, or alleged medicine, where it is not
really needed, and indeed often where the buoyancy of mind, which
is the real curative agent, can only be created by making him wait
hopefully for the expected action of medicine; and some physicians
still cannot unlearn their old training. But the change is great.
The modern treatment of disease relies very greatly on the old
so-called natural methods, diet and exercise, bathing and massage,
in other words giving the natural forces the fullest scope by easy
and thorough nutrition, increased flow of blood, and removal of
obstructions to the excretory systems or the circulation in the
tissues. One notable example is typhoid fever. At the outset of the
nineteenth century it was treated with “remedies” of the extremest
violence,--bleeding and blistering, vomiting and purging, antimony
and calomel, and other heroic remedies. Now the patient is bathed
and nursed and carefully tended, but rarely given medicine. This
is the result partly of the remarkable experiments of the Paris
and Vienna schools into the action of drugs which have shaken the
stoutest faiths; and partly of the constant and reproachful object
lesson of homeopathy. No regular physician would ever admit that the
homeopathic “infinitesimals” could do any good as direct curative
agents; and yet it was perfectly certain that homeopaths lost no more
of their patients than others. There was but one conclusion to draw,
that most drugs had no effect whatever on the diseases for which they
were administered.”--“Encyclopædia Americana,” Vol. X. (Munn & Co.,
New York.)
=Applying Hygienic Tests Systematically.=--The cause of ill health
(_e.g._ a headache) should be sought with system and thoroughness,
applying the tests in rotation to every function of the body:
_Lungs._ Is the air habitually breathed fresh and free from dust?
Is the body held up, and is the chest or waist cramped by clothing?
_Muscles._ Is enough physical exertion made to cause deep breaths
to be drawn? _Food._ Is it simple, digestible, and eaten properly?
_Drink._ Is the water pure? _Cleanliness_, _Work and Rest_,
_Clothing_, _Ventilation_, and _Mental State_ may be inquired into
until the source of trouble is found and the cause of ill health
removed. To give drugs and leave the cause of ill health untouched,
is to fail. There are signs of coming weakness or illness which, if
heeded and the ways of living improved, will usually prevent illness.
Among these signs are headaches, paleness, sensitiveness to cold,
heavy feeling or pain after meals, constipation. Huxley says that
young people should so learn physiology and so understand their
bodies that they will _heed the first sign of nature’s displeasure,
and not wait for a box on the ear_.
=Nervous Children.=--A report on the health of the school children
in one of our large cities shows that one third of the children in
those schools have some disorder of the nerves. Nervousness (weakened
control of the nerves) may show itself by sluggishness of mind,
great _irritability of temper_, frequent _spells of the_ “_blues_,”
or by _involuntary movements_ of a _jerky_ or fidgety kind. Sound
development of city children’s nerves is hindered because of the
constant noise in cities both day and night; by _shortening of the
hours of sleep_; by _excessive use of sugar_ for food; by living much
among people with _no chance to be alone and let the nerves rest_,
and among boys by the _use of cigarettes_.
=How to Prevent the School from injuring Children.=--(1) _Ventilation_
is of first importance. Breathing the breath of fifty other children
does far more harm than overstudy. (2) _The time devoted to work_
should not be long, especially in the lower grades (no study out
of school). (3) The _work should be diversified_; not only printed
words, but pictures, natural objects, and the outdoor world should
be studied. (4) The teacher and parent should see that _the habitual
poise_ of the child is favorable to health. (5) The children should
be _encouraged to play_. Running games at recess are of the greatest
value, and are as indispensable to the health of a boy or girl as of
a colt. (6) _Physical exercise_ should be provided at short intervals
between lessons, especially _stretching exercises_ and _movements that
straighten the spine and hips and elevate the chest_.
=The Effect of Alcohol upon Nerve Function.=--In attacking the nerve
centers, alcohol begins with the cerebrum, the highest, and proceeds
toward the lowest. Hence as a man becomes drunk he first talks
foolishly (cerebrum affected), then he staggers (cerebellum affected),
and he finally goes to sleep and breathes very hard (medulla affected)
in a drunken stupor. It rarely happens that the breathing center is
completely disabled and the man dies from the strong poison. The
greatest evil of alcohol is seen in the case of steady drinking. This
gradually destroys the soundness of the nervous system and weakens
self-control. The tendency with nearly all drinkers is to increase the
amount taken.
=Not Total Abstainers, but the Advocates of Universal Moderation are
the Visionaries.=--The evil results from alcohol are so great as to
be almost incredible. The plainest statements of its effects are
sometimes denounced as unscientific by persons prejudiced in its favor.
A part of the two billion dollars annually paid for liquors is used in
influencing public opinion through the press.
PRACTICAL QUESTIONS.--=1.= Why does travel often cure a sick person
when all else fails? =2.= Why is working more healthful than “taking
exercise”? (p. 47.) =3.= Is it better for children to play or to
take exercise? =4.= Why can one walk and carry on a conversation at
the same time? (p. 127.) =5.= How does indigestion cause a headache?
(p. 133.) =6.= Does perfectly comfortable clothing from head to foot
help to make one at ease in company? Does uncomfortable clothing tend
to make one awkward? =7.= Why is it as important to have the shoes
and clothes perfectly comfortable when going out as when staying
at home? =8.= When one’s finger is cut, where is the pain? =9.= In
what two ways may opening a window when a student is becoming dull
and drowsy at his books enable him to wake up and study with ease?
=10.= What kinds of cells shrivel like a baked apple when they become
fatigued? (Fig. 117.) =11.= A nerve or nerve fiber can hardly become
tired or fatigued, for the nerve cell supplies the energy. What
do we mean when we say the nerves are worn out? (Fig. 117.) =12.=
Why do you throw cold water upon a fainting person? =13.= Why does
constant, moderate drinking undermine the health more than occasional
intoxication? =14.= Why does stoppage of the circulation cause one
to faint? (See Chap. VI.) =15.= Why is grazing the skin often more
painful than cutting it? (Colored Fig. 1.) =16.= Why do the lower
animals always act upon sudden impulse? What part of the brain
enables man to retain sensations and not act upon them until later?
=17.= Does “nervousness” more probably indicate a bright mind or a
high temper? =18.= What is the effect of a cold bath upon the nerves?
(Chap. II.) =19.= Did you ever know a cigarette smoker whose hand
trembled? =20.= Need there be any fear of a sobbing child holding
its breath until it dies? =21.= Why is muscle tone greater in cold
weather?
=The True Function of Stimulants.=--One whose heart has nearly given
out because of exposure to severe weather may be temporarily revived
by alcohol. _It will not be wise to do so unless it is certain that a
warm fire and protection will be reached before the reaction comes._
Much less would be necessary to revive an abstainer than a drunkard.
_Habitually_ disturbing the body with stimulants makes them ineffective
in a time of emergency. A cup of coffee will not keep a watcher awake
if he is used to coffee.
=Definitions: Stimulant, Narcotic, Poison.=--_A stimulant is
anything that excites the body to activity, but is of no help or of
insignificant help, in replacing the strength used up._
_A narcotic is anything that deadens or dulls the nervous system._ It
comes from a word meaning “to benumb.”
_Poisons_ are active substances, which, taken in quantities, as man
takes food, destroy life; in smaller quantities they injure the body
and may destroy life. Alcohol is a poison. Wine, beer, whisky, contain
varying quantities of it.
=The Narcotic and Stimulant Effects of Poisons.=--Examples of poisons
are alcohol, nicotin, opium, arsenic, strychnin. Poisons excite the
body when taken in small doses, while in large doses they produce
paralysis and death. _The irritating or stimulating effect is due to_
derangement of the functions or to the efforts of the cells to free the
body of the destructive substance. _The narcotic effect is due to_ the
poison having so benumbed the nerves and injured the cells that their
activities cease, or become less for a time. You readily see how the
same poison can be both a stimulant and a narcotic: _the stimulating
effect always comes first, followed by the stupefying effect_. If the
dose is very small, the stimulating effect will last longer; if it is
large, the narcotic effect is greater and felt more quickly. A habit
of using stimulants is an invariable sign of weakness. The first dose
of morphine or cocaine may be the first step in a lifelong blight
of strength and happiness. If physicians whose treatment of a case
results in leaving a patient with a drug or alcohol habit were sued for
malpractice, they would be less reckless. The annual consumption of
morphine is estimated at twenty-seven grains per capita in China, and
fifty grains in the United States.
=Reaction.=--_This is the depressed and exhausted condition that comes
on after a period of unnatural activity._ It follows the exciting
effects of a stimulant.
=Natural Stimulants.=--If there were nothing to arouse activity, life
would be impossible. A cold wind is a natural stimulant. _The activity
aroused by a cold wind is just enough to help the body withstand the
cold; artificial stimulants cause an expenditure having no relation
to the needs of the body._ Hence there is a great waste of energy.
Feelings may stimulate, as love for his family may stimulate a man to
labor. The desire for knowledge may stimulate a boy to study. Hunger
may stimulate a man to eat. Hunger is a natural stimulant, and is not
likely to make him eat to excess; tea, coffee, pepper, etc., arouse
a false appetite. These things are used chiefly for their stimulant
effect, for they contain little or no nourishment. We will now
study about artificial stimulants. _Such stimulants always cause an
unregulated and unhealthy action, and are always followed by reaction._
=How much Strength is stored in the Body?=--Dr. Tanner of Minnesota
believed that most people eat too much. _Another physician said that
no human being could go forty days without food._ Dr. Tanner made the
experiment. He lost thirty-six pounds in weight, but he weighed 121¹⁄₂
pounds and had considerable strength at the end of the forty days. The
first thing he ate at the close of his fast was the juice of a ripe
watermelon.
Once some miners were shut in by the caving of a part of a mine. But,
unlike the case just described, _they were without water as well as
food_. When, by digging, the rescuers reached them seven days after,
several were still found alive, although most of them had died. The
miners, no doubt, had nourishment in their bodies for some weeks more
of life, but the body lacked water to dissolve it and bring it within
the reach of the cells most needing it.
=A Stupendous Fact.=--These incidents show how wisely the body is made,
and prove that the cells store up nourishment for weeks ahead. _The
large amount of nourishment stored in the human body_ is one of the
most striking and important facts with which the science of physiology
has to deal, and it should be borne in mind, or we may make great
mistakes about some very simple matters and especially in regard to the
effects of stimulants.
=Foolish Rashness.=--Did you ever get so tired that you had to give
up and stop, however much you would have liked to continue at work or
play? _To rest was the wise thing to do._ Because you know there is
much energy stored in the body, this need not tempt you to go on until
you almost break down. Probably you know _people who are conceited
about their bodies_ and say they are “made of cast iron”; that nothing
can hurt them. Such conceit will be almost sure to get its possessor
into trouble.
=How a Safeguard may be broken down.=--It is a very wise arrangement
that, _under ordinary conditions, we cannot get at the surplus energy
we have_. Carbon dioxid and other wastes accumulate in the tissues
and paralyze the nerves. Fatigue and other feelings compel us to be
provident, as it were; yet stimulants and narcotics, by irritating the
nerve cells, arouse them and cause us to expend some of this reserve
energy. Thus man is enabled to get at this precious store which he
should save for emergencies, when he is sick and cannot digest food,
or when he is making some mighty effort. A weak, ill man who has eaten
very little for weeks, when delirious is sometimes so powerful that it
takes several strong men to hold him in bed. But the delirious mania
often uses up the little energy left, and costs the man his life.
=The only source of energy for man’s body= is the union of food and
oxygen; he must get his energy from the same source that the engine
does; and this is from his food, which serves as fuel, and the
oxygen which burns it. If one has been working hard preparing for
examinations, or gathering hay, or in attending to some important
business, or has been under the excitement of some pleasure trip, and
_feels “blue” and worn out, then let him bear the result like a man_,
or like a true boy or girl, as the case may be. Giving up for a while,
or “toughing it out” with the blues, or losing a little time from
business, will not hurt, but will restore strength, while a stimulant
will leave him less of a man than before.
=Nervousness.=--The attempt to divide the race into brain workers,
muscle workers, and loafers, whether men or women, is a powerful
factor in race degeneration. Leonard Hill says: “Hysteria and nervous
exhaustion are the fruits not of overwork, but of lack of varied and
interesting employment. The absurd opinion that hard work is menial
and low, leads to most pernicious consequences. The girl who, turning
from brain work to manual labor, can cook, scrub, wash, and garden,
invites the bloom of health to her cheeks; while the fine do-nothing
lady loses her good looks, suffers from the blues, and is a nuisance
to her friends and a misery to herself.” A Japanese lady holds views
similar to those of Dr. Hill. Read footnote.[10]
[10] =Statement by Madame Toyi Niku= of Yeddo, Japan, after a six
months’ visit to the United States.--“Worry and inactivity, it seems
to me, sharply mark the women of your middle classes. I did not
attempt to study your leaders of society, for they are much alike
the world over--the same fuss, the same display of jewels and
finery, the same scandals, the same uselessness. Your women do not
diversify enough. If they are good cooks, they stop there; perhaps
another is a good housekeeper, another can sew finely; but doing one
thing makes narrow-mindedness. In Japan we strive to do many things.
The worry troubles of your women, it seems to me, come largely from
improper eating and overeating. I have sat at many of your tables
and there is too much food on them and too much variety. First,
women overeat, then they doctor, then they starve, and then they
become nervous. A woman’s diet, especially a mother’s, should always
be simple. Cut down eating and increase variety of labor and
exercise. My own people live that way with a result that we have
better feminine bodies, better skins, and better tempers than your
women. I like the brightness of your young women. Perhaps you will
take the hideous hats off them some day, find a substitute for the
bad corset, and let them wear clothes that are loose, yet are soft
and clinging. They are bound up in their clothes too much now and
their judgment of colors and combinations is not good. Their
clothing is either garish or very dull in hue. The simplest girl in
Japan knows how to harmonize color with herself.”--_Mother’s
Magazine_, November, 1907.
SUBJECTS FOR DEBATE.--(1) Does the Chinese woman deform her body less
than the Caucasian woman and suffer less from it? (2) Does as much
disease originate in the dining room as the barroom? (3) Are drugs a
necessary evil? (4) Does pride cause as much illness as ignorance?
(5) Is it ever right to neglect the health? (6) Does the mind or the
way of living have more effect upon the health?
=Disuse and Degeneration.=--Many persons in civilized countries
cherish a vain hope of having sound muscles without habitual use
of them, pure blood without deep breathing, a strong circulation
in an inactive body, a fresh skin without keeping the body sound,
a hearty appetite without enough physical labor to use the food
already eaten, steady nerves with a part of the body overworked
and a part stagnating from disuse. Their flabby muscles, pale
skins, highly seasoned food to arouse appetite, narcotics to deaden
irritable nerves, and the wide use of drugs as a fancied substitute
for right living all show the attempt to be a miserable failure.
If the parents leading such a life escape with fairly good health
and average length of life, they leave a few unhealthy children in
whom physical degeneration is plain. Complete, balanced living only
prevents degeneration. Although there are cases of illness which are
not necessarily a disgrace, disease usually originates in weakness of
character or lack of common sense. The snob who thinks himself above
physical labor, the dupes who at the bidding of avaricious fashion
mongers think more of clothes than of a free body, the narrow,
unbalanced man, who concentrates all his energies on one ambition,
the short-sighted one who worries, all grow into a diseased state.
CHAPTER IX
THE SENSES
_Experiment 1._ =Where are the Nerves of Touch most Abundant?=--Open
a pair of scissors so that the points are one eighth of an inch
apart, and touch both points to the tip of the finger. Are they felt
as one or as two points? Find how far they must be separated to be
felt as two points when applied to the back of the neck. Record
results. Caution: The person should be blindfolded, or should look
away while the tests are being made. Two pins stuck in a cork will be
more convenient to use than scissors.
_Experiment 2._ =Nerves of Temperature, or Thermic Nerves.=--Draw the
end of a cold wire along the skin. Does the wire feel cold all the
time? Repeat with a hot wire. Do you conclude that temperature is
felt only in spots?
[Illustration: FIG. 119.--“COLD” SPOTS (light shading). “HOT” SPOTS
(dark), skin of thigh.]
=Muscular Sense.=--_Experiment 3._ Make tests of the ability to
distinguish the weight of objects weighing nearly the same, when
laid by another in outstretched hand; also by laying them in the
hand while it rests upon a table. Which test showed more delicate
distinctions? In which were muscles brought into use? _Experiment 4._
Close the eyes and let some one move your left arm to a new position;
then see if you can with the forefinger of the right hand touch the
forefinger of the left hand in its new position at the first attempt.
_Experiment 5._ =Functions of the Several Parts of the Tongue.=--Test
the tip, edges, and back of the tongue with sugar, vinegar, quinine,
and salt. Where is the taste of each most acute? Record results.
=Flavors.=--_Experiment 6._ Blindfold a member of the class, and
while he holds his nostrils firmly closed by pinching them, have him
place successively upon his tongue a bit of potato and of onion.
Can he distinguish them? _Experiment 7._ Mark _F_ after each of the
following foods that have a flavor (see text): vanilla, apple, lemon,
beef, peaches, grapes, coffee, onion, potato, cinnamon.
_Experiment 8._ =A Smelling Contest.=--Place the following and other
things having taste in vials around which paper has been pasted to
conceal their contents: pepper sauce, vinegar, kerosene, flavoring
extracts (diluted), several perfumes, iodine, bits of banana, lemon,
apple, etc. Number the vials and have pupils test and write results
in a list. Correct the lists and announce pupil having keenest sense
of smell.
_Experiment 9._ =A tasting contest= may be arranged in a similar way.
Smelling and tasting tests should be made quickly as these senses are
soon dulled by repeating a sensation.
_Experiment 10._ =Advantage of Two Eyes over One.=--Try to touch
forefinger to something held by another at arm’s length from you,
bringing the finger in from the side: (1) with one eye closed; (2)
with both eyes open. Result? Conclusion? We tell the distance of an
object by the amount of convergence of the eyeballs needed to look at
it.
_Experiment 11._ =Duration of Impression.=--Whirl a stick with a
glowing coal on one end (see Fig. 123).
_Experiment 12._ =Color Blindness.=--Provide a number of yarns of
different tints, and the same tints. Test color blindness by having
each pupil match tints and assort the yarns.
_Experiment 13._ =Fatigue of Optic Nerve.=--Gaze long and steadily at
a moderately bright object, then close the eyes. Result? Conclusion?
_Experiment 14._ =Dissection of Eye.=--The eye of an ox is an
interesting subject for dissection. The lens is like a clear crystal.
Make out all parts named in the text (see Fig. 122).
_Experiment 15._ =Image formed by a Convex Lens.=--For a few cents
obtain from a jeweler a convex lens, or use a strong pair of
spectacles worn by an old person. Hold the lens a few feet from a
window (darken any other windows near). A little beyond the lens hold
a white card or book open at a blank page to catch the image. Have
some one walk before the window.
_Experiment 16._ =Work of Iris.=--Notice the size of the pupils.
Cover one eye with the hand for a few minutes. Uncover and look
in a mirror. Gaze at bright window and look again in the mirror.
Conclusion? Do the two pupils still keep the same size when one eye
is shaded?
_Experiment 17._ =Accommodation.=--By holding your finger or a pencil
in line with writing on the blackboard, you find that you cannot see
both finger and blackboard distinctly at the same time--first one and
then the other is distinct. Explain (see text).
_Experiment 18._ =Astigmatism= (effect of unequal curvature of cornea
or lens along certain lines). With end of crayon draw about twelve
straight, even lines crossing at one point on the blackboard. Have
the lines of equal distinctness. How many pupils report that the
lines in certain directions are blurred? Inquire whether these pupils
have frequent headaches from eye strain.
_Experiment 19._ =Can Sound reach the Ear through the Bones?=--Hold a
watch between the lips and notice its ticking. Close the teeth down
upon it and notice any change in the sound. Cover one, then both
ears, and note the result.
_Experiment 20._ =Test keenness of hearing= by having pupils walk
away from a ticking watch until it becomes inaudible. Test each ear.
A “stop” watch is preferable.
_Experiment 21._ =Advantage of Two Ears over One.=--Have the class
stand in a circle. Blindfold some one and place him in the middle of
the circle. Let various pupils clap the hands as the teacher points
to each. Can the blindfolded one point in the direction whence the
sound comes? Stop one ear with a handkerchief and repeat. Result?
Conclusion? From what two points in the circle does the sound fall
upon both ears alike?
_Experiment 22._ =The Cause of Nasal Tones.=--Let a pupil go to the
back of the room and read a paragraph, and hold his nose until partly
through the reading. Or the teacher may read with his face and hand
hidden by a large book. Let the other pupils raise their hands when
they notice a change in the quality of the reader’s voice. Does the
experiment show that a “nasal” tone comes partly through the nose
or through the mouth only? Does stoppage of the nostrils by catarrh
cause a nasal tone?
=Five Differences between Special and General Sensation.=--First, the
nerves of special sense all end in special organs at the surface; for
instance, the touch corpuscles are for touch, the eye is for sight,
etc. There are many nerves in the body that do _not end in special
organs_; these nerves give what is called general sensation. A second
difference is that general sensation _tells of the condition of
the interior of the body_, while special sensations tell us of the
condition of the surface of the body and of the outside world. Third,
_general sensations are not so exact_ as the reports of the special
senses. One can locate a point on the skin that has been touched
much more accurately than he can locate an internal pain. A fourth
difference is that the meaning of each special sensation must be
learned (usually in infancy); but the _meaning of general sensations
is inherited_. This inherited knowledge of what general sensations
mean is also called instinct. Fifth, the _sympathetic nerves usually
bring general sensations_; the spinal and cranial nerves usually
bring special sensations.
=Examples of general sensations= are hunger, thirst, satiety,
nausea, faintness, giddiness, fatigue, weight, aching, shuddering,
restlessness, blues, creepy feeling, tingling, sleepiness, pain,
illness. Any nerve can convey the general sensation of pain, if
injured along its course. If a nerve of touch is cut, there is no
sensation of touch, but of pain. Touch sensations come only from the
ends of the nerves. General sensations are of many kinds. We are
only half conscious of some of them; many of them are hard even to
describe.
=Hygiene of the General Sensations.=--General sensation is an
invaluable aid to the health. Without it as a guide, the body could
not remain alive a single day. _Pain_ should be heeded as our best
friend, and not killed with poisonous drugs as if it were our worst
enemy. We should not deaden the stomach ache with an after-dinner
cigar. If we do not go to bed when sleepy, the _desire for sleep_ may
leave us, and we will undergo untold suffering from sleeplessness.
_Thirst_ should be satisfied with cool water, which quenches it the
best; he who makes his teeth ache with ice water will inflame his
stomach and be continually thirsty. He who does not stop eating when
his _hunger_ is satisfied, will distend his stomach with food, and
the stretched organ will be harder to satisfy thereafter; in fact,
eating after a feeling of satiety may cause indigestion so that the
cells will not get the food. A dyspeptic is always hungry, for the
cells are starving. _Fatigue_ of body or mind gives us wise counsel;
but this feeling may be deadened by alcohol or tobacco, and work
continued until the body is injured. We should heed the warning of
pain or fatigue or restlessness as promptly as an engineer heeds
a red flag on the railway track. One who uses narcotics acts like
a reckless engineer who removes the danger signal and goes ahead,
hoping by good luck to escape an accident.
Most of the =nerves of touch= end in papillæ of the dermis as
_microscopic, egg-shaped bodies_ (Fig. 120). There are also many in
the interior of the mouth, especially on the tongue. On the palms they
are arranged in curved lines, and on the tips of the fingers they are
in circular lines, with one papilla in the center. The delicacy of the
sense of touch varies very much in different parts of the skin. _This
delicacy refers to two things_: the ability to feel the slightest
pressure and the ability to tell the exact point of the skin that is
touched. A lighter pressure can be felt on the forehead and temples
than with any part of the body. (Why is it best for this to be the
case?) The greatest delicacy in locating the point of the skin touched
is found to be located in the tip of the tongue, the lips, and the
ends of the fingers (Exp. 1). (Why is it best that this is so?) This
delicacy is least in the middle of the back. The delicacy varies with
the number of touch corpuscles in different parts of the skin. The
sense of touch is capable of great cultivation, as in the case of the
blind.
[Illustration: FIG. 120.--DIFFERENT KINDS OF TOUCH BODIES AT ENDS OF
NERVES.
_A_, from cornea of the eye; _B_, from the tongue of a duck; _C_, _D_,
_E_, from the skin of the fingers. (Jegi.)]
=The temperature sense= is given by special nerves called the thermic
nerves (Exp. 2). That the _thermic nerves are easily fatigued_ is
noticed soon after entering a bath of hot water; it is also shown
by the fact that in cold countries the nose or ears of a person may
freeze without his feeling it.
=The Muscular Sense.=--_The special sense of touch gives some sense
of weight._ A weight upon the skin must be increased by one third
before it feels heavier, but by lifting an object so as to _bring
into action the muscular sense residing in nerves ending in the
muscles_ an increase of only one seventeenth of the original weight
can be noticed (Exp. 3). This sense gives us a continual _account of
the position of the limbs_ (Exp. 4).
=The end organs of taste= are located in the papillæ of the tongue. The
tongue has a fuzzy look because of the numerous papillæ.
=The principal tastes= are only four; namely, sweet (tasted chiefly by
tip of tongue), sour and saline (sides of tongue), bitter (tasted on
the back of tongue) (Exp. 5).
=The nerves of smell= end in the mucous membrane of the upper half
of the two nasal chambers; the _fibers are spread over the upper
proportion of the walls_. The direct current of air does not pass as
high as these nerve endings; hence sniffing aids the perception of
odors. This sense is able to bring up the associations of early life
more powerfully than any of the senses. The odor of a flower like one
that grew in an old garden can almost restore the consciousness of the
past. _We smell gases only_; solids and liquids cannot affect this pair
of nerves (Exp. 8).
=Flavors.=--The tastes that we call flavors are really smells. We
confuse them with taste, because they accompany food that is in the
mouth. Name some foods that seem “tasteless” when one has a severe
cold in the head. Why is this? Some of the most repulsive drugs can be
easily swallowed if the nose is held (Exp. 6 and 7).
=Hygiene of the Senses of Taste and Smell.=--A savage or a beast
uses the senses of taste and smell to find out whether things are
good to eat or not. If a civilized man’s senses are not perverted,
and he eats only simple foods that have a pleasant taste, they will
not injure him or cause him sickness. Things that are poisonous
usually have unpleasant tastes and often have unpleasant odors. These
senses are naturally of wonderful delicacy. They can be cultivated
to a still more remarkable degree, or they can be blunted and almost
destroyed. Chronic catarrh dulls or destroys the sense of smell. The
loss or even the weakening of the perception of flavors is an injury
to the working of the closely related sense of taste. When a person
loses the enjoyment of delicate flavors, he wants food to have strong
seasoning and more decided taste to prevent it from being insipid.
Everything must be either very greasy or very sweet or very salty or
very sour, to please his degenerate senses. Wheat, corn, and other
grains have each its own pleasant taste, yet such persons must have
lard in their bread because they are not capable of appreciating
anything with a delicate taste. In England, butter is not salted and
its delicate taste is enjoyed; in America, salt is added to preserve
it, and most people have come to prefer the strong taste of salty
butter to the delicate taste of pure butter, and do not like it
unless its true taste is partly hidden by the taste of salt (Exp. 9).
=Deceiving the Sense of Taste.=--The habit of using narcotics like
_tea_ and _coffee_ is usually begun by concealing the repulsive
bitter taste of the substance by mixing sugar, cream, and other
agreeable things with it. Licorice is sometimes mixed with _tobacco_
to weaken its biting taste. _Pure alcohol_ would never be drunk by
any one who had the least respect for the sense of taste, but the
agreeable flavor of grapes, apples, and other fruit which still
remains in wine, cider, and brandy, conceals the repulsive taste
of the alcohol. _Beer_ has the insipid taste of grain which has
undergone decomposition or partial rotting, and hops are added
because the strong bitter taste of hops is needed to hide the
stale, rancid taste of the rotted grain. _Eggnog_ is made of eggs,
a nourishing food; sugar, which has an agreeable taste; water, a
refreshing drink, and alcohol, a fiery poison. A very good eggnog is
often made without alcohol, but a good one could hardly be made with
any of the pleasant ingredients left out. The best eggnog is made by
using the fresh juice of lemon, orange, or grape, instead of alcohol.
=Effect of Narcotics.=--Tobacco, alcohol, opium, and other narcotics
dull the senses of taste and smell and prevent the enjoyment of
delicate flavors. They accomplish this as much by their effect upon
the brain as upon the nerves themselves.
=It is Wrong to eat Food that is not Relished.=--Unpalatable food is
not likely to be well digested. It is a law of the body that _the
food which is enjoyed the most is digested the best_. This applies
to a hungry person eating food with its own honest taste, not to
food disguised by the taste of something else. The rule does not
apply to a taste perverted by having been forced to become accustomed
to poisonous things. People who munch their food slowly enjoy the
pleasures of taste the most, and digest their food the best. The
nerves of taste and smell easily become fatigued. The first whiff
from a cologne bottle is the strongest. Highly flavored foods should
be eaten moderately, if we would obtain the greatest enjoyment from
them.
THOUGHT QUESTIONS.--=1. Interfering with the Body.= What is the
natural direction of growth of the big toe? =2.= Think of six evil
results, direct or indirect, which will follow from displacing it by
tight shoes (p. 48). =3.= Which part of the spinal column, designed
in infinite wisdom to be most flexible, do some people try to make
the most inflexible? =4.= The mobility of the false and floating ribs
was intended as a blessing. Some people interpret the blessing as an
opportunity to do what? =5.= Name six articles which warn us to avoid
them by their bitter, burning, or nauseating tastes, yet which are
used by man. =6.= Name six feelings which are intended as warnings
for our guidance, but which are commonly disregarded.
=The eyes= on the rays of the starfish are mere spots of pigment.
Insects have lenses in their eyes. The eyes of vertebrates are all
formed on the same general plan as the human eye.
=The eyeballs= are globes about an inch in diameter. They are placed in
deep, bony sockets, called _orbits_, in the front part of the skull.
The optic nerve, other nerves, and several large blood vessels pass to
the eye through a hole in the back of the orbit. A soft cushion of fat
is in the orbit behind the eyeball. A pressure upon the eyeball causes
the eye to sink into the socket, for the fat yields to the pressure.
This is a protection to the eye.
=The eyelids= protect the eyes from dust, and at times from the light.
They are aided in this by the eyelashes.
[Illustration: FIG. 121.--TEAR GLANDS AND DUCTS of right eye. (Jegi.)]
=The tears= are formed by _tear glands_ situated above the eyeball in
the portion of the orbit farthest from the nose, just beneath the bony
brow where it feels the sharpest (Fig. 121). They are about the size of
almonds. A saltish liquid is continually oozing from the tear glands
and passing over the eyeball; it is carried into the nose through the
_nasal duct_ (Fig. 121). The tears reach this duct through _two small
canals_, which open into the eye in the little fleshy elevation at
the inner corners of the eye (Fig. 121). The opening of one of the
canals may be seen by looking into a mirror. Sometimes these canals are
stopped up, and what is called a “weeping eye” results. A temporary
stoppage may occur during a cold in the head.
Tears prevent friction between eye and lid. Winking applies the tears
to the ball. Small glands along the edges of the lids form a kind
of oil which usually prevents the tears from flowing over the lids.
Sometimes this oily secretion is so abundant, especially during sleep,
as to cause the lids to stick together. The mucous membrane of the
eyelids continues as a transparent membrane (the conjunctiva) which
passes over the front of the ball.
[Illustration: FIG. 122.--THE ANATOMY OF THE EYE.]
=The globe of the eye= consists of its outer wall and the soft contents
(Fig. 122). The wall has three layers or coats. The outer coat is
the tough _sclerotic_ (Greek, _skleros_, hard), composed of dense
connective tissue (Exp. 14). It gives strength and firmness to the
eyeball. It shows between the lids as the “white of the eye.” It is
white and opaque except in front; there it bulges out to form the
transparent _cornea_. This clear portion of the wall may be seen by
looking at the eye of another from the side.
The second coat, called the _choroid_, consists of blood vessels and
a loose connective tissue containing many dark brown or black pigment
granules. The choroid absorbs superfluous light. Cats’ eyes shine at
night because this coat in their eyes reflects some light. The choroid
separates from the sclerotic toward the front of the eye and forms the
colored _iris_. The iris makes the eyes beautiful, and it also serves
the useful purpose of regulating the amount of light. The hole in the
iris is called the _pupil_ (Exp. 15).
The third and innermost coat, the sensitive pinkish layer called the
_ret′in-a_, is the most important and characteristic tissue in the eye.
It receives the light rays, and retains the image for a fraction of a
second (Exp. 11). Hence the pictures in a kinetoscope (Fig. 123) appear
as one moving picture. The retina is made chiefly of the fibers of the
optic nerve. This nerve contains about five hundred thousand fibers,
and enters at the back of the ball. The spot where it enters contains
no nerve endings and is not sensitive to light. It is called the _blind
spot_. The spot where the light most often falls is most sensitive to
light. It is the _yellow spot_ (Fig. 122).
[Illustration: FIG. 123.--STROBOSCOPE, the original of the kinetoscope.
The observer looks through the slits of a rapidly revolving disk and a
new image falls on the retina before the last image has faded. Compare
the pictures in the figure.]
=Test for the Blind Spot.=--In this experiment shut the right eye and
be careful not to let the left eye waver.
* Read this line slowly. Can you see the star all the time? (If so,
hold the book farther or closer and repeat.)
=Within the coats of the ball=, like the pulp within the rind of an
orange, are the soft contents, divided into three parts. The first is
a watery liquid in front, which serves to keep the cornea bulged out
(Fig. 122). It is called the _a′que-ous humor_. The main cavity of the
ball is occupied by a clear, jellylike substance called the _vit′re-ous
humor_, which serves to keep the ball distended. Back of the iris, and
separating the two humors just named, is the _crys′tal-line lens_, a
beautiful clear lens, convex or rounded out on both sides (Exp. 14).
It serves to bring the light to a focus on the retina, thereby forming
images of outside objects.
=The eye, like a camera=, has a dark lining, the choroid; the retina
corresponds to the sensitive plate, and the lens brings the rays to a
focus on it and forms the image.
[Illustration: FIG. 124.--CROSSING OF OPTIC NERVES showing that one
nerve reaches same half of both eyes.]
=The Path of Light in the Eye.=--The light enters through the
transparent cornea and passes through the aqueous humor. As it goes
through the pupil, the iris shuts off all the light that is not needed.
The crystalline lens receives the light that has been allowed to pass,
and so bends the rays that by the time they have passed through the
vitreous humor they fall upon the retina in just the right way to form
a tiny image of anything outside (Exp. 11). The choroid absorbs any
light that passes the retina. The iris and choroid of albinos have no
pigment; hence albinos squint their eyes to shut out some of the light.
=Accommodation.=--In order to focus the light upon the retina, the
_lens must change shape for every change in the distance of the object
looked at_ (see Fig. 125). The shape of the lens can be readily
changed, for it is elastic and has muscular fibers around its edges
(Exp. 17).
[Illustration: FIG. 125.--Change of lens in accommodation. (Jegi.)]
=Defects in the Eye.=--Some eyeballs are too long, and the lens
brings the rays to a focus before they reach the retina. Such eyes
are _nearsighted_ (Fig. 126) and require glasses that round inward
(concave). Some eyeballs are too flat, and the rays are not brought to
a focus soon enough. Such eyes are _farsighted_ and require glasses
that round outward (convex). See Fig. 127. (Repeat Exp. 15.)
[Illustration: FIG. 126.--(1) NEARSIGHTED EYE (ball too long), which
only focuses rays for near objects (2) when concave glasses are used
(3).]
[Illustration: FIG. 127.--FARSIGHTED EYE (ball too short) which needs
convex lens to focus rays upon retina.]
=Care of the Eyes.=--Because the eyes can do a large amount of work
without giving pain, they are often abused. When reading or doing
intricate work, turn the eyes from the work occasionally and look at
some distant object; stop work before the eyes are tired. Twilight of
early evening has ruined many good eyes. You should always stop work
before the twilight begins, for the light fades so gradually that you
will surely be straining the eyes before you know it. Do not work with
the light in front; the glare of the light makes objects appear dim.
The light should come from above, and (for right-handed people) from
the left. Do not read papers or books printed in fine type. We should
not read when convalescing from illness; with the head bent down; when
the eyes are sore; in jolting cars. Heating the eyes by a burner,
or drying the eyeballs in a dry, stove-heated atmosphere, using a
light without a shade, cause trouble with students’ eyes. Of what are
blood-shot eyes often a sign? Our eyes are best suited for seeing at
a distance because primitive man had no houses, books, sewed clothes.
Effort is required to shape the lens for seeing near objects. Most
cases of nearsightedness begin when children are taught to read under
eight years old. The eyes are sometimes injured by the use of tobacco.