slip, over the water containing the torn fragments. Absorb the excess
of moisture at the edge of the cover, by pressing a bit of
blotting-paper against it for a moment. Place it on the stage of a
microscope and examine with highest obtainable power, by light
reflected upward from the mirror beneath the stage. Note the apparent
size of the finest fibers; the striation of the fibers, or their
markings, consisting of alternate dim and bright cross bands. Note the
arrangement of the fibers in bundles, each thread running parallel with
its neighbor.
Experiment 25. _To examine the minute structure of involuntary muscular
fiber, a tendon, or a ligament._ Obtain a very small portion of the
muscular coat of a cow’s or a pig’s stomach. Put it to soak in a
solution of one dram of bichromate of potash in a pint of water. Take
out a morsel on the slip of glass, and tease as directed for the
voluntary muscle. Examine with a high power of the microscope and note:
(1) the isolated cells, long and spindle-shaped, that they are much
flattened; (2) the arrangement of the cells, or fibers, in sheets, or
layers, from the torn ends of which they project like palisades.
Experiment 26. Tease out a small portion of the tendon or ligament in
water, and examine with a glass of high power. Note the large fibers in
the ligament, which branch and interlace.
Experiment 27. With the head slightly bent forwards, grasp between the
fingers of the right hand the edge of the left sterno-cleido-mastoid,
just above the collar bone. Raise the head and turn it from left to
right, and the action of this important muscle is readily seen and
felt. In some persons it stands out in bold relief.
Experiment 28. The tendons which bound the space (popliteal) behind the
knee can be distinctly felt when the muscles which bend the knee are in
action. On the outer side note the tendons of the biceps of the leg,
running down to the head of the fibula. On the inside we feel three
tendons of important muscles on the back of the thigh which flex the
leg upon the thigh.
Experiment 29. _To show the ligamentous action of the muscles._
Standing with the back fixed against a wall to steady the pelvis, the
knee can be flexed so as to almost touch the abdomen. Take the same
position and keep the knee rigid. When the heel has been but slightly
raised a sharp pain in the back of the thigh follows any effort to
carry it higher. Flexion of the leg to a right angle, increases the
distance from the lines of insertion on the pelvic bones to the
tuberosities of the tibia by two or three inches—an amount of
stretching these muscle cannot undergo. Hence the knee must be flexed
in flexion of the hip.
Experiment 30. A similar experiment may be tried at the wrist. Flex the
wrist with the fingers extended, and again with the fingers in the
fist. The first movement can be carried to 90°, the second only to 30°,
or in some persons up to 60°. Making a fist had already stretched the
extensor muscles of the arm, and they can be stretched but little
farther. Hence, needless pain will be avoided by working a stiff wrist
with the parts loose, or the fingers extended, and not with a clenched
fist.
Review Analysis: Important Muscles
Location. Name. Chief Function.
Head and Neck. Occipito-frontalis. moves scalp and raises eye brow.
Orbicularis palpebrarum. shuts the eyes.
Levator palpebrarum. opens the eyes.
Temporal. raise the lower jaw.
Masseter. ” ” ” ”
Sterno-cleido-mastoid. depresses head upon neck and neck upon chest.
Platysma myoides. depresses lower jaw and lower lip.
Trunk. Pectoralis major. draws arm across front of chest.
Pectoralis minor. depresses point of shoulder,
Latissimus dorsi. draws arm downwards and backwards.
Serratus magnus. assists in raising ribs.
Trapezius. Rhomboideus. backward movements of head and shoulder,
Intercostals. raise and depress the ribs.
External oblique. various forward movements of trunk
Internal oblique.
Rectus abdominis. compresses abdominal viscera and acts upon pelvis.
Upper Limbs. Deltoid. carries arm outwards and upwards.
Biceps. flexes elbow and raises arm.
Triceps. extends the forearm.
Brachialis anticus. flexor of elbow.
Supinator longus. flexes the forearm.
Flexor carpi radialis. flexors of wrist.
Flexor carpi ulnaris. ” ” ” ”
Lower Limbs. Gluteus maximus. adducts the thigh.
Adductors of thigh. draw the leg inwards.
Sartorius. crosses the legs.
Rectus femoris. flexes the thigh.
Vastus externus. extensor of leg.
Vastus internus. extensor of leg upon thigh.
Biceps femoris. flexes leg upon thigh.
Gracilis. flexes the leg and adducts thigh.
Tibialis anticus. draws up inner border of foot.
Peroneus longus. raises outer edge of foot,
Gastrocnemius. keep the body erect, and
Soleus. aid in walking and running.
Chapter IV.
Physical Exercise.
80. Importance of Bodily Exercise. Nothing is so essential to success
in life as sound physical health. It enables us to work with energy and
comfort, and better to endure unusual physical and mental strains.
While others suffer the penalties of feebleness, a lower standard of
functional activities, and premature decay, the fortunate possessor of
a sound mind in a sound body is better prepared, with proper
application, to endure the hardships and win the triumphs of life[13].
This element of physical capacity is as necessary to a useful and
energetic life, as are mental endowment and intellectual acquirement.
Instinct impels us to seek health and pleasure in muscular exercise. A
healthy and vigorous child is never still except during sleep. The
restless limbs and muscles of school children pent up for several
hours, feel the need of movement, as a hungry man craves food. This
natural desire for exercise, although too often overlooked, is really
one of the necessities of life. One must be in ill health or of an
imperfect nature, when he ceases to feel this impulse. Indeed, motion
within proper bounds is essential to the full development and perfect
maintenance of the bodily health. Unlike other machines, the human body
becomes within reasonable limits, stronger and more capable the more it
is used.
As our tenure of life at best is short, it is our duty to strive to
live as free as possible from bodily ills. It is, therefore, of
paramount importance to rightly exercise every part of the body, and
this without undue effort or injurious strain.
Strictly speaking, physical exercise refers to the functional activity
of each and every tissue, and properly includes the regulation of the
functions and movements of the entire body. The word exercise, however,
is used usually in a narrower sense as applied to those movements that
are effected by the contraction of the voluntary muscles.
Brief reference will be made in this chapter only to such natural and
systematic physical training as should enter into the life of every
healthy person.
81. Muscular Activity. The body, as we have learned, is built up of
certain elementary tissues which are combined to make bones, muscles,
nerves, and other structures. The tissues, in turn, are made up of
countless minute cells, each of which has its birth, lives its brief
moment to do its work in the animal economy, is separated from the
tissue of which it was a part, and is in due time eliminated by the
organs of excretion,—the lungs, the skin, or the kidneys. Thus there is
a continuous process of growth, of decay, and removal, among the
individual cells of each tissue.
Note. The Incessant Changes in Muscular Tissue. “In every tiny block of
muscle there is a part which is really alive, there are parts which are
becoming alive, there are parts which have been alive, and are now
dying or dead; there is an upward rush from the lifeless to the living,
a downward rush from the living to the dead. This is always going on,
whether the muscle be quiet and at rest, or whether it be active and
moving,—some of the capital of living material is being spent, changed
into dead waste; some of the new food is always being raised into
living capital. But when the muscle is called upon to do work, when it
is put into movement, the expenditure is quickened, there is a run upon
the living capital, the greater, the more urgent the call for
action.”—Professor Michael Foster.
These ceaseless processes are greatly modified by the activity of the
bodily functions. Every movement of a muscle, for instance, involves
change in its component cells. And since the loss of every atom of the
body is in direct relation to its activity, a second process is
necessary to repair this constant waste; else the body would rapidly
diminish in size and strength, and life itself would soon end. This
process of repair is accomplished, as we shall learn in Chapters VI.
and VII., by the organs of nutrition, which convert the food into
blood.
Illustration: Fig. 39.—Showing how the Muscles of the Back may be
developed by a Moderate Amount of Dumb-Bell Exercise at Home. (From a
photograph.)
82. Effect of Exercise upon the Muscles. Systematic exercise influences
the growth and structure of the muscles of the body in a manner
somewhat remarkable. Muscular exercise makes muscular tissue; from the
lack of it, muscles become soft and wasted. Muscles properly exercised
not only increase in size, both as a whole and in their individual
structure, but are better enabled to get rid of material which tends to
hamper their movements. Thus muscular exercise helps to remove any
needless accumulation of fat, as well as useless waste matters, which
may exist in the tissues. As fat forms no permanent structural part of
the organism, its removal is, within limits, effected with no
inconvenience.
Muscular strength provides the joints with more powerful ligaments and
better developed bony parts. After long confinement to the bed from
disease, the joints have wasted ligaments, thin cartilages, and the
bones are of smaller proportions. Duly exercised muscles influence the
size of the bones upon which they act. Thus the bones of a
well-developed man are stronger, firmer, and larger than those of a
feeble person.
He who has been physically well trained, has both a more complete and a
more intelligent use of his muscles. He has acquired the art of causing
his muscles to act in concert. Movements once difficult are now carried
on with ease. The power of coördination is increased, so that a desired
end is attained with the least amount of physical force and nervous
energy. In learning to row, play baseball, ride the bicycle, or in any
other exercises, the beginner makes his movements in a stiff and
awkward manner. He will use and waste more muscular force in playing
one game of ball, or in riding a mile on his wheel, than an expert
would in doing ten times the work. He has not yet learned to balance
one set of muscles against their antagonists.
Illustration: Fig. 40.—The Standard Special Chest Weight.
A convenient machine by means of which all the muscles of the body may
be easily and pleasantly exercised with sufficient variations in the
movements to relieve it of monotony.
A space 6 ft wide, 6 ft deep, and 7 ft high nearly in front of the
machine is required for exercise.]
In time, however, acts which were first done only with effort and by a
conscious will, become automatic. The will ceases to concern itself. By
what is called reflex action, memory is developed in the spinal cord
and the muscular centers (sec. 273). There is thus a great saving of
actual brain work, and one important cause of fatigue is removed.
83. Effect of Exercise on Important Organs. The importance of regular
exercise is best understood by noting its effects upon the principal
organs of the body. As the action of the heart is increased both in
force and frequency during exercise, the flow of blood throughout the
body is augmented. This results from the force of the muscular
contractions which play their part in pressing the blood in the veins
onward towards the heart. Exercise also induces a more vigorous
respiration, and under increased breathing efforts the lung capacity is
increased and the size of the chest is enlarged. The amount of air
inspired and expired in a given time is much larger than if the body
were at rest. The blood is thus supplied with a much larger amount of
oxygen from the air inhaled, and gives off to the air a corresponding
excess of carbon dioxid and water.
Again, exercise stimulates and strengthens the organs of digestion. The
appetite is improved, as is especially noted after exercise in the open
air. The digestion is more complete, absorption becomes more rapid, the
peristaltic movements of the bowels are promoted, and the circulation
through the liver is more vigorous. More food is taken to supply the
force necessary for the maintenance of the mechanical movements. Ample
exercise also checks the tendency towards a torpid circulation in the
larger digestive organs, as the stomach and the liver, so common with
those who eat heartily, but lead sedentary lives. In short, exercise
may be regarded as a great regulator of nutrition.
Exercise increases the flow of blood through the small vessels of the
skin, and thus increases the radiation of heat from the surface. If the
exercise be vigorous and the weather hot, a profuse sweat ensues, the
rapid evaporation of which cools the body. The skin is thus a most
important regulator of the bodily temperature, and prevents any rise
above the normal which would otherwise result from vigorous exercise.
(See secs. 226 and 241).
84. Effect of Exercise upon the Personal Appearance. Judicious and
systematic exercise, if moderately employed, soon gives a more upright
and symmetrical figure, and an easier and more graceful carriage.
Rounded shoulders become square, the awkward gait disappears, and there
is seen a graceful poise to the head and a bearing of the body which
mark those whose muscles have been well trained. A perfectly formed
skeleton and well-developed muscles give the graceful contour and
perfect outline to the human body. The lean, soft limbs of those who
have never had any physical education, often look as if they belonged
to persons recovering from sickness. The effects of sound physical
exercise are well exhibited in the aspect of the neck, shoulders, and
chest of one who has been well trained. This is noticeable in gymnasts
and others who practice upon the horizontal bar, with chest weights,
dumb-bells, and other apparatus which develop more especially the
muscles of the upper half of the trunk.
Illustration: Fig. 41.—Young Woman practicing at Home with the “Whitely
Exerciser.” (From a photograph)
Exercise improves the condition of the tissues generally. They become
more elastic, and in all respects sounder. The skin becomes firm,
clear, and wholesome. Hence, every part of the surface of the body
rapidly takes on a change in contour, and soon assumes that appearance
of vigor and soundness which marks those of firm physical condition.
The delicate, ruddy aspect of the complexion, the swing about the body
and the bearing of the head and shoulders, of young women whose
physical training has been efficient, are in marked contrast with those
characteristics in persons whose education in this respect has been
neglected.
85. Effect of Unsuitable or Excessive Exercise. But exercise, like
everything else which contributes to our welfare, may be carried to
excess. The words excessive and unsuitable, when applied to muscular
exertion, are relative terms, and apply to the individual rather than
to amount of work done. Thus what may be excessive for one person,
might be suitable and beneficial to another. Then the condition of the
individual, rather than the character of the muscular work, is always a
most important factor.
Breathlessness is, perhaps, the most common effect of undue exertion.
Let a middle-aged person, who is out of practice, run a certain
distance, and he is soon troubled with his breathing. The respirations
become irregular, and there is a sense of oppression in his chest. He
pants, and his strength gives out. His chest, and not his legs, has
failed him. He is said to be “out of breath.” He might have practiced
dumb-bells or rowed for some time without inconvenience.
The heart is often overstrained, and at times has been ruptured during
violent exertion, as in lifting an immense weight. The various forms of
heart-disease are common with those whose occupations involve severe
muscular effort, as professional athletes and oarsmen. Hæmorrhages of
various kinds, especially from the lungs, or rupture of blood-vessels
in the brain, are not uncommon results of over-exertion.
Excessive repetition of muscular movements may lead to permanent
contractions of the parts involved. Thus sailors, mechanics, and others
frequently develop a rigidity of the tendons of the hand which prevents
the full extension of the fingers. So stenographers, telegraphers and
writers occasionally suffer from permanent contractions of certain
muscles of the arm, known as writer’s cramp, due to their excessive
use. But the accidents which now and then may result from severe
physical exertion, should discourage no one from securing the benefits
which accrue from moderate and reasonable exercise.
86. Muscular Fatigue. We all know how tiresome it is to hold the arm
outstretched horizontally even for a few moments. A single muscle, the
deltoid, in this case does most of the work. Even in a vigorous man,
this muscle can act no longer than four to six minutes before the arm
drops helpless. We may prolong the period by a strong effort of the
will, but a time soon comes when by no possible effort are we able to
hold out the arm. The muscle is said to be fatigued. It has by no means
lost its contractile power, for if we apply a strong electric stimulus
to it, the fatigue seems to disappear. Thus we see the functional power
of a muscle has a definite limit, and in fatigue that limit is reached.
Illustration: Fig. 42.—A Well-Equipped Gymnasium. (From a photograph.)
The strength of the muscle, its physical condition, the work it has
done, and the mental condition of the individual, all modify the state
of fatigue. In those difficult acts which involve a special effort of
the will, the matter of nerve exhaustion is largely concerned. Thus,
the incessant movements in St. Vitus’ dance result in comparatively
little fatigue, because there is no association of the brain with the
muscular action. If a strong man should attempt to perform voluntarily
the same movements, he would soon have to rest. None of the movements
which are performed independently of the will, as the heart-beats and
breathing movements, ever involve the sensation of fatigue. As a result
of fatigue the normal irritability of muscular tissue becomes weakened,
and its force of contraction is lessened. There is, also, often noticed
in fatigue a peculiar tremor of the muscles, rendering their movements
uncertain. The stiffness of the muscles which comes on during severe
exercise, or the day after, are familiar results of fatigue.
This sense of fatigue should put us on guard against danger. It is a
kind of regulator which serves in the ordinary actions of life to warn
us not to exceed the limits of useful exercise. Fatigue summons us to
rest long before all the force of the motor organs has been expended,
just as the sensation of hunger warns us that we need food, long before
the body has become weak from the lack of nourishment.
We should never forget that it is highly essential to maintain an
unused reserve of power, just as a cautious merchant always keeps at
the bank an unexpended balance of money. If he overspends his money he
is bankrupt, and the person who overspends his strength is for the time
physically bankrupt. In each case the process of recovery is slow and
painful.
87. Rest for the Muscles. Rest is necessary for the tissues, that they
may repair the losses sustained by work; that is, a period of rest must
alternate with a period of activity. Even the heart, beating
ceaselessly, has its periods of absolute rest to alternate with those
of work. A steam-engine is always slowly, but surely, losing its
fitness for work. At last it stops from the need of repair. Unlike the
engine, the body is constantly renewing itself and undergoing continual
repair. Were it not for this power to repair and renew its various
tissues, the body would soon be worn out.
This repair is really a renovation of the structure. Rest and work are
relative terms, directly opposed to each other. Work quickens the pulse
and the respiration, while rest slows both. During sleep the voluntary
muscles are relaxed, and those of organic life work with less energy.
The pulse and the respiration are less frequent, and the temperature
lower than when awake. Hence sleep, “tired Nature’s sweet restorer,”
may be regarded as a complete rest.
The periods of rest should vary with the kind of exercise. Thus
exercise which produces breathlessness requires frequent but short
rests. The trained runner, finding his respiration embarrassed, stops a
moment to regain his breath. Exercises of endurance cause fatigue less
quickly than those of speed, but require longer rest. Thus a man not
used to long distances may walk a number of hours without stopping, but
while fatigue is slow to result, it is also slow to disappear. Hence a
lengthy period of rest is necessary before he is able to renew his
journey.
88. Amount of Physical Exercise Required. The amount of physical
exercise that can be safely performed by each person, is a most
important and practical question. No rule can be laid down, for what
one person bears well, may prove very injurious to another. To a
certain extent, each must be guided by his own judgment. If, after
taking exercise, we feel fatigued and irritable, are subject to
headache and sleeplessness, or find it difficult to apply the mind to
its work, it is plain that we have been taxing our strength unduly, and
the warnings should be heeded.
Age is an important factor in the problem, as a young man may do with
ease and safety, what might be injurious to an older person. In youth,
when the body is making its most active development, the judicious use
of games, sports, and gymnastics is most beneficial. In advanced life,
both the power and the inclination for exercise fail, but even then
effort should be made to take a certain reasonable amount of exercise.
Abundant evidence shows that physical development is most active from
thirteen to seventeen years of age; this manifests itself clearly by
increase in weight. Hence this period of life is of great consequence.
If at this age a boy or girl is subjected to undue physical strain, the
development may suffer, the growth be retarded, and the foundation laid
for future ill health.
Illustration: Fig. 43.—Student exercising in the School Gymnasium on
the Rowing Machine. (From a photograph.)
The proper amount of exercise must vary greatly with circumstances. It
may be laid down as a fairly safe rule, that a person of average height
and weight, engaged in study or in any indoor or sedentary occupation,
should take an amount of exercise equivalent to walking five or six
miles a day. Growing children, as a rule, take more exercise than this,
while most men working indoors take far less, and many women take less
exercise than men. Exercise may be varied in many ways, the more the
better; but for the most part it should always be taken in the open
air.
89. Time for Exercise. It is not prudent to do hard work or take severe
exercise, just before or just after a full meal. The best time is one
or two hours after a meal. Vigorous exercise while the stomach is
busily digesting food, may prove injurious, and is apt to result sooner
or later in dyspepsia. On the other hand, severe exercise should not be
taken on an empty stomach. Those who do much work or study before
breakfast, should first take a light lunch, just enough to prevent any
faint feeling. With this precaution, there is no better time for
moderate exercise than the early morning.
In the case of children, physical exercises should not be undertaken
when they are overtired or hungry. Neither is it judicious for adults
to take vigorous exercise in the evening, after a long and arduous
day’s work.
90. Walking, Running, and Jumping. Walking is generally regarded as the
simplest and most convenient mode of taking exercise. Man is
essentially a walking animal. When taken with a special object in view,
it is the best and most pleasant of all physical activities. It is
suited for individuals of all ages and occupations, and for residents
of every climate. The child, the athlete, and the aged are all able to
indulge in this simple and effective means of keeping the body in
health.
In walking, the muscles of the entire body are brought into action, and
the movements of breathing and the circulation of the blood are
increased. The body should be erect, the chest thrown out, the head and
shoulders held back, and the stride long and elastic. It is an
excellent custom to add to the usefulness of this fine exercise, by
deep, voluntary inhalations of pure air.
Running is an excellent exercise for children and young people, but
should be sparingly indulged in after the age of thirty-five. If it be
accompanied with a feeling of faintness, breathlessness, and
palpitation of the heart, the exercise is too severe, and its
continuance may do serious harm. Running as an exercise is beneficial
to those who have kept themselves in practice and in sound condition.
It brings into play nearly every muscle of the body, and thus serves to
develop the power of endurance, as well as strength and capacity for
rapid movement.
Jumping may well be left to boys and young men under twenty, but
skipping with a rope, allied to jumping, is an admirable and beneficial
form of exercise. It brings into action many muscles without putting
undue strain upon any particular group.
91. Skating, Swimming, and Rowing. Skating is a delightful and
invigorating exercise. It calls into play a great variety of muscles,
and is admirably adapted for almost all ages. It strengthens the ankles
and helps give an easy and graceful carriage to the body. Skating is
especially valuable, as it can be enjoyed when other out-door exercises
are not convenient.
Every child above ten years of age should be taught to swim. The art,
once mastered, is never forgotten. It calls into use a wide combination
of muscles. This accomplishment, so easily learned, should be a part of
our education, as well as baseball or bicycling, as it may chance to
any one to save his own life or that of a companion.
In many respects rowing is one of the most perfect exercises at our
command. It expands the chest, strengthens the body, and gives tone to
the muscles of the abdomen. It is very suitable for girls and women, as
no other exercise is so well adapted to remedy the muscular defects so
marked in their sex. Even elderly persons can row day after day without
difficulty. The degree of muscular effort required, can be regulated so
that those with weak hearts and weak lungs can adjust themselves to the
exercise.
92. Bicycling as an Exercise. The bicycle as a means of taking exercise
has come into popular use with remarkable rapidity. Sharp competition
bids fair to make the wheel more popular and less expensive than ever.
Its phenomenal use by persons of all ages and in all stations of life,
is proof of the enthusiasm with which this athletic exercise is
employed by women as well as by men.
Mechanical skill has removed most of the risks to health and person
which once existed. A good machine, used by its owner with judgment, is
the most convenient, the safest, and the least expensive means of
traveling for pleasure or exercise. It is doing more than any other
form of exercise to improve the bodily condition of thousands whose
occupations confine them all day to sedentary work. Dependent upon no
one but himself, the cyclist has his means of exercise always at hand.
No preparation is necessary to take a spin of ten miles or so on the
road, during a summer evening or before breakfast.
Bicycling brings into active use the muscles of the legs as well as
those of the trunk and arms. It seems to benefit those who suffer from
dyspepsia, constipation, and functional disorders of the liver.
A special caution must be used against overdoing in cycling, for the
temptation by rivalry, making a record, by social competition on the
road, is stronger in this form of exercise than in any other,
especially for young folks. Many cases have occurred of permanent
injury, and even loss of life, from collapse simply by excessive
exertion and exhaustion.
93. Outdoor Games and Physical Education. While outdoor games are not
necessary to maintain health, yet we can scarcely overestimate the part
that the great games of baseball, football, tennis, golf, and croquet,
play in the physical development of young people. When played in
moderation and under suitable conditions, they are most useful and
beneficial exercises. They are played in the open air, and demand a
great variety of vigorous muscular movement, with a considerable amount
of skill and adroitness of action. These games not only involve
healthful exercise, but develop all those manly and wholesome qualities
so essential to success in life.
A vigorous body is well-nigh essential to success, but equally
important are readiness of action, sound judgment, good temper,
personal courage, a sense of fair play, and above all, a spirit of
honor. Outdoor games, when played in a reasonable and honorable manner,
are most efficient and practical means to develop these qualities in
young people.
94. The School and Physical Education. The advantages to be derived,
during the school period, from the proper care and development of the
body, should be understood and appreciated by school officials,
teachers, and parents. The school period is the best time to shape the
lives of pupils, not mentally or morally alone, but physically as well.
This is the time, by the use of a few daily exercises at school, to
draw back the rounding shoulders, to form the habit of sitting and
standing erect, to build up strong and comely arms and chests, and
otherwise to train pupils to those methods which will serve to ripen
them into vigorous and well-knit men and women.
Teachers can by a little effort gain the knowledge requisite properly
to instruct their pupils in a few systematic exercises. Gratifying
results will follow just as the teacher and pupils evince interest and
judgment in the work. It is found by experience that pupils are not
only quick to learn, but look forward eagerly to the physical exercises
as an interesting change from the routine of school life.
There should be a stated time for these school exercises, as for any
other duty. There can be practiced in the schoolroom a great variety of
interesting and useful exercises, which call for little or no expense
for apparatus. Such exercises should no more interfere with the
children’s usual games than any other study does. Under no
circumstances should the play hours be curtailed.
95. Physical Exercises in School. Physical exercises of some sort,
then, should be provided for pupils in our schools, especially in large
towns and cities, where there is little opportunity for outdoor games,
and they should form a part of the regular course of study. The object
should be the promotion of sound health rather than the development of
muscle, or performing feats of agility or strength. Exercises with
dumb-bells and wands, or even without any apparatus, practiced a few
times a day, for five minutes at a time, do a great deal of good. They
relax the tension of body and mind, and introduce an element of
pleasure into the routine of school life. They increase the breathing
power and quicken the action of the heart.
Illustration: Fig. 44.—Physical Exercises as carried on in Schools.
(From photographs.)
Note. “In early boyhood and youth nothing can replace the active sports
so much enjoyed at this period; and while no needless restrictions
should be placed upon them, consideration should be paid to the amount,
and especially to the character, of the games pursued by delicate
youth. For these it would be better to develop the weakened parts by
means of systematic physical exercises and by lighter sports.”—Dr. John
M. Keating on “Physical Development” in Pepper’s _Cyclopædia of the
Diseases of Children_.
If vigorously and systematically carried out, these exercises
invigorate all the tissues and organs of the body, and stimulate them
to renewed activity. They serve to offset the lack of proper
ventilation, faulty positions at the desks, and the prolonged inaction
of the muscles. To secure the greatest benefit from physical training
in school, it is important that the pupils be interested in these
exercises, and consider them a recreation, and not a task[14].
96. Practical Points about Physical Exercise. The main object in
undertaking systematic and graduated physical exercises is not to learn
to do mere feats of strength and skill, but the better to fit the
individual for the duties and the work of life. Exercises should be
considered with reference to their availability from the learner’s
standpoint. The most beneficial exercises ordinarily are the gentle
ones, in which no strain is put upon the heart and the respiration. The
special aim is to secure the equal use of all the muscles, not the
development of a few. The performance of feats of strength should never
come within the scope of any educational scheme. Exercises which call
for sustained effort, violent exertion, or sudden strain are best
avoided by those who have had no preparation or training.
Regular exercise, not sudden and occasional prolonged exertion, is
necessary for health. The man or woman who works in an office or store
all the week, and on Sunday or a holiday indulges in a long spin on the
bicycle, often receives more harm than good from the exertion. Exercise
should be taken, so far as is convenient, in the open air, or in a
large and well-ventilated room.[15]
After the more violent exercises, as baseball, football, a long ride on
the bicycle, or even after a prolonged walk, a warm bath should be
taken at the first convenient opportunity. Care should be taken to rub
down thoroughly, and to change a part or all of the clothing. Exercise
is comparatively valueless until the idea of taking it for health is
quite forgotten in the interest and pleasure excited by the occasion.
No exercise should be carried to such a degree as to cause fatigue or
exhaustion. Keep warmly clad after exercise, avoid chills, and always
stop exercising as soon as fatigue is felt.
Wear clothing which allows free play to all the muscles of the body.
The clothing should be light, loose, and made of wool. Care should be
taken not to take cold by standing about in clothes which are damp with
perspiration. In brisk walking and climbing hills keep the mouth shut,
especially in cold weather, and breathe through the nose, regulating
the pace so that it can be done without discomfort.
97. Effect of Alcoholic Liquors and Tobacco upon Physical Culture. As a
result of the unusual attention given to physical culture in the last
few years, hundreds of special instructors are now employed in training
young people in the theory and practice of physical exercise. These
expert teachers, to do their work with thoroughness and discipline,
recognize the necessity of looking after the daily living of their
students. The time of rising and retiring, the hours of sleep, the
dress, the care of the diet, and many other details of personal health
become an important part of the training.
Recognizing the fact that alcoholic drink and tobacco are so disastrous
to efficiency in any system of physical training, these instructors
rigidly forbid the use of these drugs under all circumstances. While
this principle is perhaps more rigorously enforced in training for
athletic contests, it applies equally to those who have in view only
the maintenance of health.
Books on Physical Education. There are many excellent books on physical
education, which are easily obtained for reading or for reference.
Among these one of the most useful and suggestive is Blackie’s
well-known book, “How to Get Strong and how to Stay so.” This little
book is full of kindly advice and practical suggestions to those who
may wish to begin to practice health exercises at home with inexpensive
apparatus. For more advanced work, Lagrange’s “Physiology of Bodily
Exercise” and the Introduction to Maclaren’s “Physical Education” may
be consulted. A notable article on “Physical Training” by Joseph H.
Sears, an Ex-Captain of the Harvard Football Team, may be found in
Roosevelt’s “In Sickness and in Health.”
Price lists and catalogues of all kinds of gymnastic apparatus are
easily obtained on application to firms handling such goods.
Various Systems of Physical Exercises. The recent revival of popular
interest in physical education has done much to call the attention of
the public to the usefulness and importance of a more thorough and
systematic use of physical exercises, both at home and in the schools.
It is not within the scope of this book to describe the various systems
of gymnastic and calisthenic exercises now in common use in this
country. For the most part they have been modified and rearranged from
other sources, notably from the two great systems, _i.e._, Swedish and
German.
For a most comprehensive work on the Swedish system, the teacher is
referred to the “Swedish System of Educational Gymnastics,” with
264 illustrations, by Baron Nils Posse. There is also a small
manual for teachers, called “Handbook of School Gymnastics of the
Swedish Systems,” by the same author.
Chapter V.
Food and Drink.
98. Why we need Food. The body is often compared to a steam-engine in
good working order. An engine uses up fuel and water to obtain from
them the energy necessary to do its work. So, we consume within our
bodies certain nutritious substances to obtain from them the energy
necessary for our activities. Just as the energy for the working of the
engine is obtained from steam by the combustion of fuel, so the energy
possessed by our bodies results from the combustion or oxidation within
us of the food we eat. Unless this energy is provided for the body it
will have but little power of doing work, and like an engine without
steam, must soon become motionless.
99. Waste and Repair. A steam-engine from the first stroke of its
piston-rod begins to wear out, and before long needs repair. All work
involves waste. The engine, unless kept in thorough repair, would soon
stop. So with our bodies. In their living cells chemical changes are
constantly going on; energy, on the whole, is running down; complex
substances are being broken up into simpler combinations. So long as
life lasts, food must be brought to the tissues, and waste products
carried away from them. It is impossible to move a single muscle, or
even to think for one moment, without some minute part of the muscular
or brain tissue becoming of no further use in the body. The
transformation of dead matter into living tissue is the ever-present
miracle which life presents even in its lowest forms.
In childhood the waste is small, and the amount of food taken is more
than sufficient to repair the loss. Some of the extra food is used in
building up the body, especially the muscles. As we shall learn in
Chapter VIII., food is also required to maintain the bodily heat. Food,
then, is necessary for the production of energy, for the repair of the
body, for the building up of the tissues, and for the maintenance of
bodily heat.
100. Nature of the Waste Material. An ordinarily healthy person passes
daily, on an average, by the kidneys about 50 ounces of waste material,
of which 96 per cent is water, and from the intestines, on an average,
5½ ounces, a large proportion of which is water. By the skin, in the
shape of sweat and insensible perspiration, there is cast out about 23
ounces, of which 99 per cent is water; and by the lungs about 34
ounces, 10 of which are water and the remainder carbon dioxid.
Now if we omit an estimate of the undigestible remains of the food, we
find that the main bulk of what daily leaves the body consists of
water, carbon dioxid, and certain solid matters contained in solution
in the renal secretion and the sweat. The chief of these solid matters
is urea, a complex product made up of four elements,—carbon, hydrogen,
oxygen, and nitrogen. Water contains only two elements, hydrogen and
oxygen; and carbon dioxid also has only two, carbon and oxygen. Hence,
what we daily cast out of our bodies consists essentially of these four
elements in the form mainly of water, carbon dioxid, and urea.
These waste products represent the oxidation that has taken place in
the tissues in producing the energy necessary for the bodily
activities, just as the smoke, ashes, clinkers, and steam represent the
consumption of fuel and water in the engine. Plainly, therefore, if we
could restore to the body a supply of these four elements equivalent to
that cast out, we could make up for the waste. The object of food,
then, is to restore to the body an amount of the four elements equal to
that consumed. In other words, and briefly: The purpose of food is to
supply the waste of the tissues and to maintain the normal composition
of the blood.
101. Classification of Foods. Foods may be conveniently divided into
four great classes, to which the name food-stuffs or alimentary
principles has been given. They correspond to the chief “proximate
principles” of which the body consists. To one or the other of these
classes all available foods belong[16]. The classification of
food-stuffs usually given is as follows:
Proteids, or Nitrogenous Foods.
Starches and Sugars, or Carbohydrates.
Fats and Oils.
Inorganic or Mineral Foods,—Water, Salt.
102. Proteids; or Nitrogenous Foods. The proteids, frequently spoken of
as the nitrogenous foods, are rich in one or more of the following
organic substances: albumen, casein, fibrin, gelatine, myosin, gluten,
and legumin.
The type of this class of foods is albumen, well known as the white of
an egg. The serum of the blood is very rich in albumen, as is lean
meat. The curd of milk consists mainly of casein. Fibrin exists largely
in blood and flesh foods. Gelatine is obtained from the animal parts of
bones and connective tissue by prolonged boiling. One of the chief
constituents of muscular fiber is myosin. Gluten exists largely in the
cereals wheat, barley, oats, and rye. The proteid principle of peas and
beans is legumin, a substance resembling casein.
As the name implies, the proteids, or nitrogenous foods, contain
nitrogen; carbohydrates and fats, on the contrary, do not contain
nitrogen. The principal proteid food-stuffs are milk, eggs, flesh foods
of all kinds, fish, and the cereals among vegetable foods. Peas and
beans are rich in proteids. The essential use of the proteids to the
tissues is to supply the material from which the new proteid tissue is
made or the old proteid tissue is repaired. They are also valuable as
sources of energy to the body. Now, as the proteid part of its molecule
is the most important constituent of living matter, it is evident that
proteid food is an absolute necessity. If our diet contained no
proteids, the tissues of the body would gradually waste away, and death
from starvation would result. All the food-stuffs are necessary in one
way or another to the preservation of perfect health, but proteids,
together with a certain proportion of water and inorganic salts, are
absolutely necessary for the bare maintenance of animal life—that is,
for the formation and preservation of living protoplasm.
103. Starches and Sugars. The starches, sugars, and gums, also known as
carbohydrates, enter largely into the composition of foods of vegetable
origin. They contain no nitrogen, but the three elements, carbon,
hydrogen, and oxygen, the last two in the same proportion as in water.
The starches are widely distributed throughout the vegetable kingdom.
They are abundant in potatoes and the cereals, and in arrowroot, rice,
sago, and tapioca. Starch probably stands first in importance among the
various vegetable foods.
The sugars are also widely distributed substances, and include the
cane, grape, malt, maple, and milk sugars. Here also belong the gums
and cellulose found in fruit, cereals, and all vegetables which form
the basis of the plant cells and fibers. Honey, molasses, and manna are
included in this class.
The physiological value of the starches and sugars lies in the fact
that they are oxidized in the body, and a certain amount of energy is
thereby liberated. The energy of muscular work and of the heat of the
body comes largely from the oxidation, or destruction, of this class of
foods. Now, inasmuch as we are continually giving off energy from the
body, chiefly in the form of muscular work and heat, it is evident that
material for the production of this energy must be taken in the food.
The carbohydrates constitute the bulk of our ordinary food.
104. Fats and Oils. These include not only the ordinary fats of meat,
but many animal and vegetable oils. They are alike in chemical
composition, consisting of carbon and hydrogen, with a little oxygen
and no nitrogen. The principal kinds of fat used as food are the fat of
meat, butter, suet, and lard; but in many parts of the world various
vegetable oils are largely used, as the olive, palm, cotton seed,
cocoanut, and almond.
The use of the fats in the body is essentially the same as that of the
starches and sugars. Weight for weight they are more valuable than the
carbohydrates as sources of energy, but the latter are more easily
digested, and more easily oxidized in the body. An important use of
fatty foods is for the maintenance of the bodily heat. The inhabitants
of Arctic regions are thus enabled, by large use of the fat and oil
from the animals they devour, to endure safely the severe cold. Then
there is reason to believe that fat helps the digestion of other foods,
for it is found that the body is better nourished when the fats are
used as food. When more fat is consumed than is required to keep up the
bodily heat and to yield working power, the excess is stored up in
various parts of the body, making a sort of reserve fuel, which may be
drawn upon at any future time.
105. Saline or Mineral Foods. All food contains, besides the substances
having potential energy, as described, certain saline matters. Water
and salts are not usually considered foods, but the results of
scientific research, as well as the experience of life, show that these
substances are absolutely necessary to the body. The principal mineral
foods are salt, lime, iron, magnesia, phosphorus, potash, and water.
Except common salt and water, these substances are usually taken only
in combination with other foods.
These saline matters are essential to health, and when not present in
due proportion nutrition is disturbed. If a dog be fed on food freed
from all salines, but otherwise containing proper nutrients, he soon
suffers from weakness, after a time amounting to paralysis, and often
dies in convulsions.
About 200 grains of common salt are required daily by an adult, but a
large proportion of this is in our food. Phosphate of lime is obtained
from milk and meats, and carbonate of lime from the hard water we
drink. Both are required for the bones and teeth. The salts of potash,
which assist in purifying the blood, are obtained from vegetables and
fruits. An iron salt is found in most foods, and sulphur in the yolk of
eggs.
106. Water. Water is of use chiefly as a solvent, and while not
strictly a food, is necessary to life. It enters into the construction
of every tissue and is constantly being removed from the body by every
channel of waste[17].
As a solvent water aids digestion, and as it forms about 80 per cent of
the blood, it serves as a carrier of nutrient material to all the
tissues of the body.
Important Articles of Diet.
107. Milk. The value of milk as a food cannot be overestimated. It
affords nourishment in a very simple, convenient, and perfect form. It
is the sole food provided for the young of all animals which nourish
their young. It is an ideal food containing, in excellent proportions,
all the four elements necessary for growth and health in earlier youth.
Composition of Food Materials. Careful analyses have been made of the
different articles of food, mostly of the raw, or uncooked foods. As
might be expected, the analyses on record differ more or less in the
percentages assigned to the various constituents, but the following
table will give a fair idea of the fundamental nutritive value of the
more common foods:
In 100 parts Water Proteid Fat Carbohydrate Ash
Digestible Cellulose
Meat 76.7 20.8 1.5 0.3 — 1.3
Eggs 73.7 12.6 12.1 — — 1.1
Cheese 36-60 25-33 7-30 3-7 — 3.4
Cow’s Milk 87.7 3.4 3.2 4.8 — 0.7
Wheat Flour 13.3 10.2 0.9 74.8 0.3 0.5
Wheat Bread 35.6 7.1 0.2 55.5 0.3 1.1
Rye Flour 13.7 11.5 2.1 69.7 1.6 1.4
Rye bread 42.3 6.1 0.4 49.2 0.5 1.5
Rice 13.1 7.0 0.9 77.4 0.6 1.0
Corn 13.1 9.9 4.6 68.4 2.5 1.5
Macaroni 10.1 9.0 0.3 79.0 0.3 0.5
Peas and Beans 12-15 23-26 1½-2 49-54 4.7 2-3
Potatoes 75.5 2.0 0.2 20.6 0.7 1.0
Carrots 87.1 1.0 0.2 9.3 1.4 0.9
Cabbage 90 2.3 0.5 4-6 1-2 1.3
Fruit 84 0.5 — 10 4 0.5
Cheese is the nitrogenous part of milk, which has been coagulated by
the use of rennet. The curd is then carefully dried, salted, and
pressed. Cheese is sometimes difficult of digestion, as on account of
its solid form it is not easily acted upon by the digestive fluids.
108. Meats. The flesh of animals is one of our main sources of food.
Containing a large amount of proteid, it is admirably adapted for
building up and repairing the tissues of the body. The proportion of
water is also high, varying from 50 to 75 per cent. The most common
meats used in this country are beef, mutton, veal, pork, poultry, and
game.
Beef contains less fat and is more nutritious than either mutton or
pork. Mutton has a fine flavor and is easily digested. Veal and lamb,
though more tender, are less easily digested. Pork contains much fat,
and its fiber is hard, so that it is the most difficult to digest of
all the meats. Poultry and game have usually a small proportion of fat,
but are rich in phosphates and are valued for their flavor.
109. Eggs. Consisting of about two-thirds water and the rest albumen
and fat, eggs are often spoken of as typical natural food. The white of
an egg is chiefly albumen, with traces of fat and salt; the yolk is
largely fat and salts. The yellow color is due partly to sulphur. It is
this which blackens a silver spoon. Eggs furnish a convenient and
concentrated food, and if properly cooked are readily digested.
110. Fish. Fish forms an important and a most nutritious article of
diet, as it contains almost as much nourishment as butcher’s meat. The
fish-eating races and classes are remarkably strong and healthy. Fish
is less stimulating than meat, and is thus valuable as a food for
invalids and dyspeptics. To be at its best, fish should be eaten in its
season. As a rule shell-fish, except oysters, are not very digestible.
Some persons are unable to eat certain kinds of fish, especially
shell-fish, without eruptions on the skin and other symptoms of mild
poisoning.
111. Vegetable Foods. This is a large and important group of foods, and
embraces a remarkable number of different kinds of diet. Vegetable
foods include the cereals, garden vegetables, the fruits, and other
less important articles. These foods supply a certain quantity of
albumen and fat, but their chief use is to furnish starches, sugars,
acids, and salts. The vegetable foods indirectly supply the body with a
large amount of water, which they absorb in cooking.
112. Proteid Vegetable Foods. The most important proteid vegetable
foods are those derived from the grains of cereals and certain
leguminous seeds, as peas and beans. The grains when ground make the
various flours or meals. They contain a large quantity of starch, a
proteid substance peculiar to them called gluten, and mineral salts,
especially phosphate of lime. Peas and beans contain a smaller
proportion of starch, but more proteid matter, called legumin, or
vegetable casein. Of the cereal foods, wheat is that most generally
useful. Wheat, and corn and oatmeal form most important articles of
diet. Wheat flour has starch, sugar, and gluten—nearly everything to
support life except fat.
Oatmeal is rich in proteids. In some countries, as Scotland, it forms
an important article of diet, in the form of porridge or oatmeal cakes.
Corn meal is not only rich in nitrogen, but the proportion of fat is
also large; hence it is a most important and nutritious article of
food. Rice, on the other hand, contains less proteids than any other
cereal grain, and is the least nutritious. Where used as a staple
article of food, as in India, it is commonly mixed with milk, cheese,
or other nutritious substances. Peas and beans, distinguished from all
other vegetables by their large amount of proteids—excel in this
respect even beef, mutton, and fish. They take the place of meats with
those who believe in a vegetable diet.
113. Non-proteid Vegetable Foods. The common potato is the best type of
non-proteid vegetable food. When properly cooked it is easily digested
and makes an excellent food. It contains about 75 per cent of water,
about 20 per cent of carbohydrates, chiefly starch, 2 per cent of
proteids, and a little fat and saline matters. But being deficient in
flesh-forming materials, it is unfit for an exclusive food, but is best
used with milk, meat, and other foods richer in proteid substances.
Sweet potatoes, of late years extensively used as food, are rich in
starch and sugar. Arrowroot, sago, tapioca, and similar foods are
nutritious, and easily digested, and with milk furnish excellent
articles of diet, especially for invalids and children.
Explanation of the Graphic Chart. The graphic chart, on the next page,
presents in a succinct and easily understood form the composition of
food materials as they are bought in the market, including the edible
and non-edible portions. It has been condensed from Dr. W. O. Atwater’s
valuable monograph on “Foods and Diet.” This work is known as the
Yearbook of the U.S. Department of Agriculture for 1894.
KEY: 1, percentage of nutrients; 2, fuel value of 1 pound in calories.
The unit of heat, called a _calorie_, or gramme-degree, is the amount
of heat which is necessary to raise one gramme (15.43 grains) of water
one degree centigrade (1.8° Fahr.). A, round beef; B, sirloin beef; C,
rib beef; D, leg of mutton; E, spare rib of pork; F, salt pork; G,
smoked ham; H, fresh codfish; I, oysters; J, milk; K, butter; L,
cheese; M, eggs; N, wheat bread; O, corn meal; P, oatmeal; Q, dried
beans; R, rice; S, potatoes; T, sugar.
This table, among other things, shows that the flesh of fish contains
more water than that of warm-blooded animals. It may also be seen that
animal foods contain the most water; and vegetable foods, except
potatoes, the most nutrients. Proteids and fats exist only in small
proportions in most vegetables, except beans and oatmeal. Vegetable
foods are rich in carbohydrates while meats contain none. The fatter
the meat the less the amount of water. Thus very lean meat may be
almost four-fifths water, and fat pork almost one-tenth water.
COMPOSITION OF FOOD MATERIALS
Nutritive ingredients, refuse, and fuel value.
Illustration: Fig. 45.—Graphic Chart of the Composition of Food
Materials.
114. Non-proteid Animal Foods. Butter is one of the most digestible of
animal fats, agreeable and delicate in flavor, and is on this account
much used as a wholesome food. Various substitutes have recently come
into use. These are all made from animal fat, chiefly that of beef, and
are known as butterine, oleomargarine, and by other trade names. These
preparations, if properly made, are wholesome, and may be useful
substitutes for butter, from which they differ but little in
composition.
115. Garden Vegetables. Various green, fresh, and succulent vegetables
form an essential part of our diet. They are of importance not so much
on account of their nutritious elements, which are usually small, as
for the salts they supply, especially the salts of potash. It is a
well-known fact that the continued use of a diet from which fresh
vegetables are excluded leads to a disease known as scurvy. They are
also used for the agreeable flavor possessed by many, and the pleasant
variety and relish they give to the food. The undigested residue left
by all green vegetables affords a useful stimulus to intestinal
contraction, and tends to promote the regular action of the bowels.
116. Fruits. A great variety of fruits, both fresh and dry, is used as
food, or as luxuries. They are of little nutritive value, containing,
as they do, much water and only a small amount of proteid, but are of
use chiefly for the sugar, vegetable acids, and salts they contain.
In moderate quantity, fruits are a useful addition to our regular diet.
They are cooling and refreshing, of agreeable flavor, and tend to
prevent constipation. Their flavor and juiciness serve to stimulate a
weak appetite and to give variety to an otherwise heavy diet. If eaten
in excess, especially in an unripe or an overripe state, fruits may
occasion a disturbance of the stomach and bowels, often of a severe
form.
117. Condiments. The refinements of cookery as well as the craving of
the appetite, demand many articles which cannot be classed strictly as
foods. They are called condiments, and as such may be used in
moderation. They give flavor and relish to food, excite appetite and
promote digestion. Condiments increase the pleasure of eating, and by
their stimulating properties promote secretions of the digestive fluids
and excite the muscular contractions of the alimentary canal.
The well-known condiments are salt, vinegar, pepper, ginger, nutmeg,
cloves, and various substances containing ethereal oils and aromatics.
Their excessive use is calculated to excite irritation and disorder of
the digestive organs.
118. Salt The most important and extensively used of the condiments is
common salt. It exists in all ordinary articles of diet, but in
quantities not sufficient to meet the wants of the bodily tissues.
Hence it is added to many articles of food. It improves their flavor,
promotes certain digestive secretions, and meets the nutritive demands
of the body. The use of salt seems based upon an instinctive demand of
the system for something necessary for the full performance of its
functions. Food without salt, however nutritious in other respects, is
taken with reluctance and digested with difficulty.
Salt has always played an important and picturesque part in the history
of dietetics. Reference to its worth and necessity abounds in sacred
and profane history. In ancient times, salt was the first thing placed
on the table and the last removed. The place at the long table, above
or below the salt, indicated rank. It was everywhere the emblem of
hospitality. In parts of Africa it is so scarce that it is worth its
weight in gold, and is actually used as money. Torture was inflicted
upon prisoners of state in olden times by limiting the food to water
and bread, without salt. So intense may this craving for salt become,
that men have often risked their liberty and even their lives to obtain
it.
119. Water. The most important natural beverage is pure water; in fact
it is the only one required. Man has, however, from the earliest times
preferred and daily used a variety of artificial drinks, among which
are tea, coffee, and cocoa.
All beverages except certain strong alcoholic liquors, consist almost
entirely of water. It is a large element of solid foods, and our bodies
are made up to a great extent of water. Everything taken into the
circulating fluids of the body, or eliminated from them, is done
through the agency of water. As a solvent it is indispensable in all
the activities of the body.
It has been estimated that an average-sized adult loses by means of the
lungs, skin, and kidneys about eighty ounces of water every twenty-four
hours. To restore this loss about four pints must be taken daily. About
one pint of this is obtained from the food we eat, the remaining three
pints being taken as drink. One of the best ways of supplying water to
the body is by drinking it in its pure state, when its solvent
properties can be completely utilized. The amount of water consumed
depends largely upon the amount of work performed by the body, and upon
the temperature.
Being one of the essential elements of the body, it is highly important
that water should be free from harmful impurities. If it contain the
germs of disease, sickness may follow its use. Without doubt the most
important factor in the spread of disease is, with the exception of
impure air, impure water. The chief agent in the spread of typhoid
fever is impure water. So with cholera, the evidence is overwhelming
that filthy water is an all-powerful agent in the spread of this
terrible disease.
120. Tea, Coffee, and Cocoa. The active principle of tea is called
theine; that of coffee, caffeine, and of cocoa, theobromine. They also
contain an aromatic, volatile oil, to which they owe their distinctive
flavor. Tea and coffee also contain an astringent called tannin, which
gives the peculiar bitter taste to the infusions when steeped too long.
In cocoa, the fat known as cocoa butter amounts to fifty per cent.
121. Tea. It has been estimated that one-half of the human race now use
tea, either habitually or occasionally. Its use is a prolific source of
indigestion, palpitation of the heart, persistent wakefulness, and of
other disorders. When used at all it should be only in moderation.
Persons who cannot use it without feeling its hurtful effects, should
leave it alone. It should not be taken on an empty stomach, nor sipped
after every mouthful of food.
122. Coffee. Coffee often disturbs the rhythm of the heart and causes
palpitation. Taken at night, coffee often causes wakefulness. This
effect is so well known that it is often employed to prevent sleep.
Immoderate use of strong coffee may produce other toxic effects, such
as muscular tremors, nervous anxiety, sick-headache, palpitation, and
various uncomfortable feelings in the cardiac region. Some persons
cannot drink even a small amount of tea or coffee without these
unpleasant effects. These favorite beverages are unsuitable for young
people.
123. Cocoa. The beverage known as cocoa comes from the seeds of the
cocoa-tree, which are roasted like the coffee berries to develop the
aroma. Chocolate is manufactured cocoa,—sugar and flavors being added
to the prepared seeds. Chocolate is a convenient and palatable form of
highly nutritious food. For those with whom tea and coffee disagree, it
may be an agreeable beverage. The large quantity of fat which it
contains, however, often causes it to be somewhat indigestible.
124. Alcoholic Beverages. There is a class of liquids which are
certainly not properly food or drink, but being so commonly used as
beverages, they seem to require special notice in this chapter. In view
of the great variety of alcoholic beverages, the prevalence of their
use, and the very remarkable deleterious effects they produce upon the
bodily organism, they imperatively demand our most careful attention,
both from a physiological and an hygienic point of view.
125. Nature of Alcohol. The ceaseless action of minute forms of plant
life, in bringing about the decomposition of the elaborated products of
organized plant or animal structures, will be described in more detail
(secs. 394-398).
All such work of vegetable organisms, whether going on in the moulding
cheese, in the souring of milk, in putrefying meat, in rotting fruit,
or in decomposing fruit juice, is essentially one of fermentation,
caused by these minute forms of plant life. There are many kinds of
fermentation, each with its own special form of minute plant life or
micro-organism.
In this section we are more especially concerned about that
fermentation which results from the decomposition of sweet fruit,
plant, or other vegetable, juices which are composed largely of water
containing sugar and flavoring matters.
This special form of fermentation is known as alcoholic or vinous
fermentation, and the micro-organisms that cause it are familiarly
termed alcoholic ferments. The botanist classes them as
_Saccharomycetes_, of which there are several varieties. Germs of
_Saccharomycetes_ are found on the surfaces and stems of fruit as it is
ripening. While the fruit remains whole these germs have no power to
invade the juice, and even when the skins are broken the conditions are
less favorable for their work than for that of the moulds,[18] which
are the cause of the rotting of fruit.
But when fruit is crushed and its juice pressed out, the
_Saccharomycetes_ are carried into it where they cannot get the oxygen
they need from the air. They are then able to obtain oxygen by taking
it from the sugar of the juice. By so doing they cause a breaking up of
the sugar and a rearrangement of its elements. Two new substances are
formed in this decomposition of sugar, viz., carbon dioxid, which
arises from the liquid in tiny bubbles, and alcohol, a poison which
remains in the fermenting fluid.
Now we must remember that fermentation entirely changes the nature of
the substance fermented. For all forms of decomposition this one law
holds good. Before alcoholic fermentation, the fruit juice was
wholesome and beneficial; after fermentation, it becomes, by the action
of the minute germs, a poisonous liquid known as alcohol, and which
forms an essential part of all intoxicating beverages.
Taking advantage of this great law of fermentation which dominates the
realm of nature, man has devised means to manufacture various alcoholic
beverages from a great variety of plant structures, as ripe grapes,
pears, apples, and other fruits, cane juices, corn, the malt of barley,
rye, wheat, and other cereals.
The process differs according to the substance used and the manner in
which it is treated, but the ultimate outcome is always the same, viz.,
the manufacture of a beverage containing a greater or less proportion
of alcoholic poison. By the process of _distillation_, new and stronger
liquor is made. Beverages thus distilled are known as ardent spirits.
Brandy is distilled from wine, rum from fermented molasses, and
commercial alcohol mostly from whiskey.
The poisonous element in all forms of intoxicating drinks, and the one
so fraught with danger to the bodily tissues, is the alcohol they
contain. The proportion of the alcoholic ingredient varies, being about
50 per cent in brandy, whiskey, and rum, about 20 to 15 per cent in
wines, down to 5 per cent, or less, in the various beers and cider; but
whether the proportion of alcohol be more or less, the same element of
danger is always present.
126. Effects of Alcoholic Beverages upon the Human System. One of the
most common alcoholic beverages is wine, made from the juice of grapes.
As the juice flows from the crushed fruit the ferments are washed from
the skins and stems into the vat. Here they bud and multiply rapidly,
producing alcohol. In a few hours the juice that was sweet and
wholesome while in the grape is changed to a poisonous liquid, capable
of injuring whoever drinks it. One of the gravest dangers of
wine-drinking is the power which the alcohol in it has to create a
thirst which demands more alcohol. The spread of alcoholism in
wine-making countries is an illustration of this fact.
Another alcoholic beverage, common in apple-growing districts, is
cider. Until the microscope revealed the ferment germ on the “bloom” of
the apple-skin, very little was known of the changes produced in cider
during the mysterious process of “working.” Now, when we see the
bubbles of gas in the glass of cider we know what has produced them,
and we know too that a poison which we do not see is there also in
corresponding amounts. We have learned, too, to trace the wrecked hopes
of many a farmer’s family to the alcohol in the cider which he provided
so freely, supposing it harmless.
Beer and other malt liquors are made from grain. By sprouting the
grain, which changes its starch to sugar, and then dissolving out the
sugar with water, a sweet liquid is obtained which is fermented with
yeast, one kind of alcoholic ferment. Some kinds of beer contain only a
small percentage of alcohol, but these are usually drunk in
proportionately large amounts. The life insurance company finds the
beer drinker a precarious risk; the surgeon finds him an unpromising
subject; the criminal court finds him conspicuous in its proceedings.
The united testimony from all these sources is that beer is
demoralizing, mentally, morally, and physically.
127. Cooking. The process through which nearly all food used by
civilized man has to pass before it is eaten is known as cooking. Very
few articles indeed are consumed in their natural state, the exceptions
being eggs, milk, oysters, fruit and a few vegetables. Man is the only
animal that cooks his food. Although there are savage races that have
no knowledge of cooking, civilized man invariably cooks most of his
food. It seems to be true that as nations advance in civilization they
make a proportionate advance in the art of cooking.
Cooking answers most important purposes in connection with our food,
especially from its influence upon health. It enables food to be more
readily chewed, and more easily digested. Thus, a piece of meat when
raw is tough and tenacious, but if cooked the fibers lose much of their
toughness, while the connective tissues are changed into a soft and
jelly-like mass. Besides, the meat is much more readily masticated and
acted upon by the digestive fluids. So cooking makes vegetables and
grains softer, loosens their structure, and enables the digestive
juices readily to penetrate their substance.
Cooking also improves or develops flavors in food, especially in animal
foods, and thus makes them attractive and pleasant to the palate. The
appearance of uncooked meat, for example, is repulsive to our taste,
but by the process of cooking, agreeable flavors are developed which
stimulate the appetite and the flow of digestive fluids.
Another important use of cooking is that it kills any minute parasites
or germs in the raw food. The safeguard of cooking thus effectually
removes some important causes of disease. The warmth that cooking
imparts to food is a matter of no slight importance; for warm food is
more readily digested, and therefore nourishes the body more quickly.
The art of cooking plays a very important part in the matter of health,
and thus of comfort and happiness. Badly cooked and ill-assorted foods
are often the cause of serious disorders. Mere cooking is not enough,
but good cooking is essential.
Experiments.
Experiments with the Proteids.
Experiment 31. As a type of the group of proteids we take the white of
egg, egg-white or egg-albumen. Break an egg carefully, so as not to mix
the white with the yolk. Drop about half a teaspoonful of the raw white
of egg into half a pint of distilled water. Beat the mixture vigorously
with a glass rod until it froths freely. Filter through several folds
of muslin until a fairly clear solution is obtained.
Experiment 32. To a small quantity of this solution in a test tube add
strong nitric acid, and boil. Note the formation of a white
precipitate, which turns yellow. After cooling, add ammonia, and note
that the precipitate becomes orange.
Experiment 33. Add to the solution of egg-albumen, excess of strong
solution of caustic soda (or potash), and then a drop or two of very
dilute solution (one per cent) of copper sulphate. A violet color is
obtained which deepens on boiling.
Experiment 34. Boil a small portion of the albumen solution in a test
tube, adding drop by drop dilute acetic acid (two per cent) until a
flaky coagulum of insoluble albumen separates.
Experiments with Starch.
Experiment 35. Wash a potato and peel it. Grate it on a nutmeg grater
into a tall cylindrical glass full of water. Allow the suspended
particles to subside, and after a time note the deposit. The lowest
layer consists of a white powder, or starch, and above it lie coarser
fragments of cellulose and other matters.
Experiment 36. Examine under the microscope a bit of the above white
deposit. Note that each starch granule shows an eccentric hilum with
concentric markings. Add a few drops of very dilute solution of iodine.
Each granule becomes blue, while the markings become more distinct.
Experiment 37. Examine a few of the many varieties of other kinds of
starch granules, as in rice, arrowroot, etc. Press some dry starch
powder between the thumb and forefinger, and note the peculiar
crepitation.
Experiment 38. Rub a few bits of starch in a little cold water. Put a
little of the mixture in a large test tube, and then fill with boiling
water. Boil until an imperfect opalescent solution is obtained.
Experiment 39. Add powdered dry starch to cold water. It is insoluble.
Filter and test the filtrate with iodine. It gives no blue color.
Experiment 40. Boil a little starch with water; if there is enough
starch it sets on cooling and a paste results.
Experiment 41. Moisten some flour with water until it forms a tough,
tenacious dough; tie it in a piece of cotton cloth, and knead it in a
vessel containing water until all the starch is separated. There
remains on the cloth a grayish white, sticky, elastic “gluten,” made up
of albumen, some of the ash, and fats. Draw out some of the gluten into
threads, and observe its tenacious character.
Experiment 42. Shake up a little flour with ether in a test tube, with
a tight-fitting cork. Allow the mixture to stand for an hour, shaking
it from time to time. Filter off the ether, and place some of it on a
perfectly clean watch glass. Allow the ether to evaporate, when a
greasy stain will be left, thus showing the presence of fats in the
flour.
Experiment 43. Secure a specimen of the various kinds of flour, and
meal, peas, beans, rice, tapioca, potato, etc. Boil a small quantity of
each in a test tube for some minutes. Put a bit of each thus cooked on
a white plate, and pour on it two or three drops of the tincture of
iodine. Note the various changes of color,—blue, greenish, orange, or
yellowish.
Experiments with Milk.
Experiment 44. Use fresh cow’s milk. Examine the naked-eye character of
the milk. Test its reaction with litmus paper. It is usually neutral or
slightly alkaline.
Experiment 45. Examine with the microscope a drop of milk, noting
numerous small, highly refractive oil globules floating in a fluid.
Experiment 46. Dilute one ounce of milk with ten times its volume of
water. Add cautiously dilute acetic acid until there is a copious,
granular-looking precipitate of the chief proteid of milk (caseinogen),
formerly regarded as a derived albumen. This action is hastened by
heating.
Experiment 47. Saturate milk with Epsom salts, or common salt. The
proteid and fat separate, rise to the surface, and leave a clear fluid
beneath.
Experiment 48. Place some milk in a basin; heat it to about 100° F.,
and add a few drops of acetic acid. The mass curdles and separates into
a solid curd (proteid and fat) and a clear fluid (the whey), which
contains the lactose.
Experiment 49. Take one or two teaspoonfuls of fresh milk in a test
tube; heat it, and add a small quantity of extract of rennet. Note that
the whole mass curdles in a few minutes, so that the tube can be
inverted without the curd falling out. Soon the curd shrinks, and
squeezes out a clear, slightly yellowish fluid, the whey.
Experiment 50. Boil the milk as before, and allow it to cool; then add
rennet. No coagulation will probably take place. It is more difficult
to coagulate boiled milk with rennet than unboiled milk.
Experiment 51. Test fresh milk with red litmus paper; it should turn
the paper pale blue, showing that it is slightly alkaline. Place aside
for a day or two, and then test with blue litmus paper; it will be
found to be acid. This is due to the fact that lactose undergoes the
lactic acid fermentation. The lactose is converted into lactic acid by
means of a special ferment.
Experiment 52. Evaporate a small quantity of milk to dryness in an open
dish. After the dry residue is obtained, continue to apply heat;
observe that it chars and gives off pungent gases. Raise the
temperature until it is red hot; allow the dish then to cool; a fine
white ash will be left behind. This represents the _inorganic matter_
of the milk.
Experiments with the Sugars.
Experiment 53. Cane sugar is familiar as cooking and table sugar. The
little white grains found with raisins are grape sugar, or glucose.
Milk sugar is readily obtained of the druggist. Prepare a solution of
the various sugars by dissolving a small quantity of each in water.
Heat each solution with sulphuric acid, and it is seen to darken or
char slowly.
Experiment 54. Place some Fehling solution (which can be readily
obtained at the drug store as a solution, or tablets may be bought
which answer the same purpose) in a test tube, and boil. If no yellow
discoloration takes place, it is in good condition. Add a few drops of
the grape sugar solution and boil, when the mixture suddenly turns to
an opaque yellow or red color.
Experiment 55. Repeat same experiment with milk sugar.
Chapter VI.
Digestion.
128. The Purpose of Digestion. As we have learned, our bodies are
subject to continual waste, due both to the wear and tear of their
substance, and to the consumption of material for the production of
their heat and energy. The waste occurs in no one part alone, but in
all the tissues.
Now, the blood comes into direct contact with every one of these
tissues. The ultimate cells which form the tissues are constantly being
bathed by the myriads of minute blood-vessels which bring to the cells
the raw material needed for their continued renewal. These cells are
able to select from the nutritive fluid whatever they require to repair
their waste, and to provide for their renewed activity. At the same
time, the blood, as it bathes the tissues, sweeps into its current and
bears away the products of waste.
Thus the waste occurs in the tissues and the means of repair are
obtained from the blood. The blood is thus continually being
impoverished by having its nourishment drained away. How, then, is the
efficiency of the blood maintained? The answer is that while the
ultimate purpose of the food is for the repair of the waste, its
immediate destination is the blood.[19]
129. Absorption of Food by the Blood. How does the food pass from the
cavity of the stomach and intestinal canal into the blood-vessels?
There are no visible openings which permit communication. It is done by
what in physics is known as _endosmotic_ and _exosmotic_ action. That
is, whenever there are two solutions of different densities, separated
only by an animal membrane, an interchange will take place between them
through the membrane.
To illustrate: in the walls of the stomach and intestines there is a
network of minute vessels filled with blood,—a liquid containing many
substances in solution. The stomach and intestinal canal also contain
liquid food, holding many substances in solution. A membrane, made up
of the extremely thin walls of the blood-vessels and intestines,
separates the liquids. An exchange takes place between the blood and
the contents of the stomach and bowels, by which the dissolved
substances of food pass through the separating membranes into the
blood.
Illustration: Fig. 46.—Cavities of the Mouth, Pharynx, etc. (Section in
the middle line designed to show the mouth in its relations to the
nasal fossæ, the pharynx, and the larynx.)
A, sphenoidal sinus;
B, internal orifice of Eustachian tube;
C, velum palati;
D, anterior pillar of soft palate;
E, posterior pillar of soft palate;
F, tonsil;
H, lingual portion of the pharynx;
K, lower portion of the pharynx;
L, larynx;
M, section of hyoid bone;
N, epiglottis;
O, palatine arch
This change, by which food is made ready to pass into the blood,
constitutes food-digestion, and the organs concerned in bringing about
this change in the food are the digestive organs.
130. The General Plan of Digestion. It is evident that the digestive
organs will be simple or complex, according to the amount of change
which is necessary to prepare the food to be taken up by the blood. If
the requisite change is slight, the digestive organs will be few, and
their structure simple. But if the food is varied and complex in
composition, the digestive apparatus will be complex. This condition
applies to the food and the digestion of man.
Illustration: Fig. 47.—Diagram of the Structure of Secreting Glands.
A, simple tubular gland;
B, gland with mouth shut and sac formed;
C, gland with a coiled tube;
D, plan of part of a racemose gland
The digestive apparatus of the human body consists of the alimentary
canal and tributary organs which, although outside of this canal,
communicate with it by ducts. The alimentary canal consists of the
mouth, the pharynx, the œsophagus, the stomach, and the intestines.
Other digestive organs which are tributary to this canal, and discharge
their secretions into it, are the salivary glands,[20] the liver, and
the pancreas.
The digestive process is subdivided into three steps, which take place
in the mouth, in the stomach, and in the intestines.
131. The Mouth. The mouth is the cavity formed by the lips, the cheeks,
the palate, and the tongue. Its bony roof is made up of the upper
jawbone on each side, and the palate bones behind. This is the _hard
palate_, and forms only the front portion of the roof. The continuation
of the roof is called the _soft palate_, and is made up of muscular
tissue covered with mucous membrane.
The mouth continues behind into the throat, the separation between the
two being marked by fleshy pillars which arch up from the sides to form
the soft palate. In the middle of this arch there hangs from its free
edge a little lobe called the uvula. On each side where the pillars
begin to arch is an almond-shaped body known as the tonsil. When we
take cold, one or both of the tonsils may become inflamed, and so
swollen as to obstruct the passage into the throat. The mouth is lined
with mucous membrane, which is continuous with that of the throat,
œsophagus, stomach, and intestines (Fig. 51).
132. Mastication, or Chewing. The first step of the process of
digestion is mastication, the cutting and grinding of the food by the
teeth, effected by the vertical and lateral movements of the lower jaw.
While the food is thus being crushed, it is moved to and fro by the
varied movements of the tongue, that every part of it may be acted upon
by the teeth. The advantage of this is obvious. The more finely the
food is divided, the more easily will the digestive fluids reach every
part of it, and the more thoroughly and speedily will digestion ensue.
The act of chewing is simple and yet important, for if hurriedly or
imperfectly done, the food is in a condition to cause disturbance in
the digestive process. Thorough mastication is a necessary introduction
to the more complicated changes which occur in the later digestion.
133. The Teeth. The teeth are attached to the upper and lower maxillary
bones by roots which sink into the sockets of the jaws. Each tooth
consists of a _crown_, the visible part, and one or more fangs, buried
in the sockets. There are in adults 32 teeth, 16 in each jaw.
Teeth differ in name according to their form and the uses to which they
are specially adapted. Thus, at the front of the jaws, the incisors, or
cutting teeth, number eight, two on each side. They have a single root
and the crown is beveled behind, presenting a chisel-like edge. The
incisors divide the food, and are well developed in rodents, as
squirrels, rats, and beavers.
Next come the canine teeth, or cuspids, two in each jaw, so called from
their resemblance to the teeth of dogs and other flesh-eating animals.
These teeth have single roots, but their crowns are more pointed than
in the incisors. The upper two are often called eye teeth, and the
lower two, stomach teeth. Next behind the canines follow, on each side,
two bicuspids. Their crowns are broad, and they have two roots. The
three hindmost teeth in each jaw are the molars, or grinders. These are
broad teeth with four or five points on each, and usually each molar
has three roots.
The last molars are known as the wisdom teeth, as they do not usually
appear until the person has reached the “years of discretion.” All
animals that live on grass, hay, corn, and the cereals generally, have
large grinding teeth, as the horse, ox, sheep, and elephant.
The following table shows the teeth in their order:
Mo. Bi. Ca. In. In. Ca. Bi. Mo.
Upper 3 2 1 2 | 2 1 2 3 = 16
| } = 32
Lower 3 2 1 2 | 2 1 2 3 = 16
The vertical line indicates the middle of the jaw, and shows that on
each side of each jaw there are eight teeth.
134. Development of the Teeth. The teeth just described are the
permanent set, which succeeds the temporary or milk teeth. The latter
are twenty in number, ten in each jaw, of which the four in the middle
are incisors. The tooth beyond on each side is an eye tooth, and the
next two on each side are bicuspids, or premolars.
The milk teeth appear during the first and second years, and last until
about the sixth or seventh year, from which time until the twelfth or
thirteenth year, they are gradually pushed out, one by one, by the
permanent teeth. The roots of the milk teeth are much smaller than
those of the second set.
Illustration: Fig. 48.—Temporary and Permanent Teeth together.
_Temporary teeth:_ A, central incisors;
B lateral incisors;
C, canines;
D, anterior molars;
E, posterior molars
_Permanent teeth:_
F, central incisors;
H, lateral incisors;
K, canines;
L, first bicuspids;
M, second biscuspids;
N, first molars
The plan of a gradual succession of teeth is a beautiful provision of
nature, permitting the jaws to increase in size, and preserving the
relative position and regularity of the successive teeth.
Illustration: Fig. 49.—Showing the Principal Organs of the Thorax and
Abdomen _in situ_. (The principal muscles are seen on the left, and
superficial veins on the right.)
135. Structure of the Teeth. If we should saw a tooth down through its
center we would find in the interior a cavity. This is the pulp cavity,
which is filled with the dental pulp, a delicate substance richly
supplied with nerves and blood-vessels, which enter the tooth by small
openings at the point of the root. The teeth are thus nourished like
other parts of the body. The exposure of the delicate pulp to the air,
due to the decay of the dentine, gives rise to the pain of toothache.
Surrounding the cavity on all sides is the hard substance known as the
dentine, or tooth ivory. Outside the dentine of the root is a substance
closely resembling bone, called cement. In fact, it is true bone, but
lacks the Haversian canals. The root is held in its socket by a dense
fibrous membrane which surrounds the cement as the periosteum does
bone.
Illustration: Fig. 50.—Section of Face. (Showing the parotid and
submaxillary glands.)
The crown of the tooth is not covered by cement, but by the hard
enamel, which forms a strong protection for the exposed part. When the
teeth are first “cut,” the surface of the enamel is coated with a
delicate membrane which answers to the Scriptural phrase “the skin of
the teeth.” This is worn off in adult life.
136. Insalivation. The thorough mixture of the saliva with the food is
called insalivation. While the food is being chewed, it is moistened
with a fluid called saliva, which flows into the mouth from six little
glands. There are on each side of the mouth three salivary glands,
which secrete the saliva from the blood. The parotid is situated on the
side of the face in front of the ear. The disease, common in childhood,
during which this gland becomes inflamed and swollen, is known as the
“mumps.” The submaxillary gland is placed below and to the inner side
of the lower jaw, and the sublingual is on the floor of the mouth,
between the tongue and the gums. Each gland opens into the mouth by a
little duct. These glands somewhat resemble a bunch of grapes with a
tube for a stalk.
The saliva is a colorless liquid without taste or smell. Its principal
element, besides water, is a ferment called _ptyalin_, which has the
remarkable property of being able to change starch into a form of
cane-sugar, known as maltose.
Thus, while the food is being chewed, another process is going on by
which starch is changed into sugar. The saliva also moistens the food
into a mass for swallowing, and aids in speech by keeping the mouth
moist.
The activity of the salivary glands is largely regulated by their
abundant supply of nerves. Thus, the saliva flows into the mouth, even
at the sight, smell, or thought of food. This is popularly known as
“making the mouth water.” The flow of saliva may be checked by nervous
influences, as sudden terror and undue anxiety.
Experiment 56. _To show the action of saliva on starch_. Saliva for
experiment may be obtained by chewing a piece of India rubber and
collecting the saliva in a test tube. Observe that it is colorless and
either transparent or translucent, and when poured from one vessel to
another is glairy and more or less adhesive. Its reaction is alkaline
to litmus paper.
Experiment 57.Make a thin paste from pure starch or arrowroot. Dilute a
little of the saliva with five volumes of water, and filter it. This is
best done through a filter perforated at its apex by a pin-hole. In
this way all air-bubbles are avoided. Label three test tubes _A, B_,
and _C_. In _A_, place starch paste; in _B_, saliva; and in _C_ one
volume of saliva and three volumes of starch paste. Place them for ten
minutes in a water bath at about 104° Fahrenheit.
Test portions of all three for a reducing sugar, by means of
Fehling’s solution or tablets.[21] _A_ and _B_ give no evidence of
sugar, while _C_ reduces the Fehling, giving a yellow or red
deposit of cuprous oxide. Therefore, starch is converted into a
reducing sugar by the saliva. This is done by the ferment ptyalin
contained in saliva.
137. The Pharynx and Œsophagus. The dilated upper part of the
alimentary canal is called the pharynx. It forms a blind sac above the
level of the mouth. The mouth opens directly into the pharynx, and just
above it are two openings leading into the posterior passages of the
nose. There are also little openings, one on each side, from which
begin the Eustachian tubes, which lead upward to the ear cavities.
The windpipe opens downward from the pharynx, but this communication
can be shut off by a little plate or lid of cartilage, the epiglottis.
During the act of swallowing, this closes down over the entrance to the
windpipe, like a lid, and prevents the food from passing into the
air-passages. This tiny trap-door can be seen, by the aid of a mirror,
if we open the mouth wide and press down the back of the tongue with
the handle of a spoon (Figs. 46, 84, and 85).
Thus, there are six openings from the pharynx; the œsophagus being the
direct continuation from it to the stomach. If we open the mouth before
a mirror we see through the fauces the rear wall of the pharynx. In its
lining membrane is a large number of glands, the secretion from which
during a severe cold may be quite troublesome.
The œsophagus, or gullet, is a tube about nine inches long, reaching
from the throat to the stomach. It lies behind the windpipe, pierces
the diaphragm between the chest and abdomen, and opens into the
stomach. It has in its walls muscular fibers, which, by their worm-like
contractions, grasp the successive masses of food swallowed, and pass
them along downwards into the stomach.
138. Deglutition, or Swallowing. The food, having been well chewed and
mixed with saliva, is now ready to be swallowed as a soft, pasty mass.
The tongue gathers it up and forces it backwards between the pillars of
the fauces into the pharynx.
If we place the fingers on the “Adam’s apple,” and then pretend to
swallow something, we can feel the upper part of the windpipe and the
closing of its lid (epiglottis), so as to cover the entrance and
prevent the passage of food into the trachea.
There is only one pathway for the food to travel, and that is down the
œsophagus. The slow descent of the food may be seen if a horse or dog
be watched while swallowing. Even liquids do not fall or flow down the
food passage. Hence, acrobats can drink while standing on their heads,
or a horse with its mouth below the level of the œsophagus. The food is
under the control of the will until it has entered the pharynx; all the
later movements are involuntary.
Illustration: Fig. 51.—A View into the Back Part of the Adult Mouth.
(The head is represented as having been thrown back, and the tongue
drawn forward.)
A, B, incisors;
C, canine;
D, E, bicuspids;
F, H, K, molars;
M, anterior pillar of the fauces;
N, tonsil;
L, uvula;
O, upper part of the pharynx;
P, tongue drawn forward;
R, linear ridge, or raphé.
139. The Stomach. The stomach is the most dilated portion of the
alimentary canal and the principal organ of digestion. Its form is not
easily described. It has been compared to a bagpipe, which it resembles
somewhat, when moderately distended. When empty it is flattened, and in
some parts its opposite walls are in contact.
We may describe the stomach as a pear-shaped bag, with the large end to
the left and the small end to the right. It lies chiefly on the left
side of the abdomen, under the diaphragm, and protected by the lower
ribs. The fact that the large end of the stomach lies just beneath the
diaphragm and the heart, and is sometimes greatly distended on account
of indigestion or gas, may cause feelings of heaviness in the chest or
palpitation of the heart. The stomach is subject to greater variations
in size than any other organ of the body, depending on its contents.
Just after a moderate meal it averages about twelve inches in length
and four in diameter, with a capacity of about four pints.
Illustration: Fig. 52.—The Stomach.
A, cardiac end;
B, pyloric end,
C, lesser curvature,
D, greater curvature
The orifice by which the food enters is called the cardiac opening,
because it is near the heart. The other opening, by which the food
leaves the stomach, and where the small intestine begins, is the
pyloric orifice, and is guarded by a kind of valve, known as the
pylorus, or gatekeeper. The concave border between the two orifices is
called the _small curvature_, and the convex as the _great curvature_,
of the stomach.
140. Coats of Stomach. The walls of the stomach are formed by four
coats, known successively from without as serous, muscular, sub-mucous,
and mucous. The outer coat is the serous membrane which lines the
abdomen,—the peritoneum (note, p. 135). The second coat is muscular,
having three sets of involuntary muscular fibers. The outer set runs
lengthwise from the cardiac orifice to the pylorus. The middle set
encircles all parts of the stomach, while the inner set consists of
oblique fibers. The third coat is the sub-mucous, made up of loose
connective tissues, and binds the mucous to the muscular coat. Lastly
there is the mucous coat, a moist, pink, inelastic membrane, which
completely lines the stomach. When the stomach is not distended, the
mucous layer is thrown into folds presenting a corrugated appearance.
Illustration: Fig. 53.—Pits in the Mucous Membrane of the Stomach, and
Openings of the Gastric Glands. (Magnified 20 diameters.)
141. The Gastric Glands. If we were to examine with a hand lens the
inner surface of the stomach, we would find it covered with little
pits, or depressions, at the bottom of which would be seen dark dots.
These dots are the openings of the gastric glands. In the form of fine,
wavy tubes, the gastric glands are buried in the mucous membrane, their
mouths opening on the surface. When the stomach is empty the mucous
membrane is pale, but when food enters, it at once takes on a rosy
tint. This is due to the influx of blood from the large number of very
minute blood-vessels which are in the tissue between the rows of
glands.
The cells of the gastric glands are thrown into a state of greater
activity by the increased quantity of blood supply. As a result, soon
after food enters the stomach, drops of fluid collect at the mouths of
the glands and trickle down its walls to mix with the food. Thus these
glands produce a large quantity of gastric juice, to aid in the
digestion of food.
142. Digestion in the Stomach. When the food, thoroughly mixed with
saliva, reaches the stomach, the cardiac end of that organ is closed as
well as the pyloric valve, and the muscular walls contract on the
contents. A spiral wave of motion begins, becoming more rapid as
digestion goes on. Every particle of food is thus constantly churned
about in the stomach and thoroughly mixed with the gastric juice. The
action of the juice is aided by the heat of the parts, a temperature of
about 99° Fahrenheit.
The gastric juice is a thin almost colorless fluid with a sour taste
and odor. The reaction is distinctly acid, normally due to free
hydrochloric acid. Its chief constituents are two ferments called
pepsin and rennin, free hydrochloric acid, mineral salts, and 95 per
cent of water.
Illustration: Fig. 54.—A highly magnified view of a peptic or gastric
gland, which is represented as giving off branches. It shows the
columnar epithelium of the surface dipping down into the duct D of the
gland, from which two tubes branch off. Each tube is lined with
columnar epithelial cells, and there is a minute central passage with
the “neck” at N. Here and there are seen other special cells called
parietal cells, P, which are supposed to produce the acid of the
gastric juice. The principal cells are represented at C.
Pepsin the important constituent of the gastric juice, has the power,
in the presence of an acid, of dissolving the proteid food-stuffs. Some
of which is converted into what are called _peptones_, both soluble and
capable of filtering through membranes. The gastric juice has no action
on starchy foods, neither does it act on fats, except to dissolve the
albuminous walls of the fat cells. The fat itself is thus set free in
the form of minute globules. The whole contents of the stomach now
assume the appearance and the consistency of a thick soup, usually of a
grayish color, known as chyme.
It is well known that “rennet” prepared from the calf’s stomach has a
remarkable effect in rapidly curdling milk, and this property is
utilized in the manufacture of cheese. Now, a similar ferment is
abundant in the gastric juice, and may be called _rennin_. It causes
milk to clot, and does this by so acting on the casein as to make the
milk set into a jelly. Mothers are sometimes frightened when their
children, seemingly in perfect health, vomit masses of curdled milk.
This curdling of the milk is, however, a normal process, and the only
noteworthy thing is its rejection, usually due to overfeeding.
Experiment 58. _To show that pepsin and acid are necessary for gastric
digestion._ Take three beakers, or large test tubes; label them _A_,
_B_, _C_. Put into _A_ water and a few grains of powdered pepsin. Fill
_B_ two-thirds full of dilute hydrochloric acid (one teaspoonful to a
pint), and fill _C_ two-thirds full of hydrochloric acid and a few
grains of pepsin. Put into each a small quantity of well-washed fibrin,
and place them all in a water bath at 104° Fahrenheit for half an hour.
Examine them. In _A_, the fibrin is unchanged; in _B_, the fibrin is
clear and swollen up; in _C_, it has disappeared, having first become
swollen and clear, and completely dissolved, being finally converted
into peptones. Therefore, both acid and ferment are required for
gastric digestion.
Experiment 59. Half fill with dilute hydrochloric acid three large test
tubes, labelled _A_, _B_, _C_. Add to each a few grains of pepsin. Boil
_B_, and make _C_ faintly alkaline with sodic carbonate. The alkalinity
may be noted by adding previously some neutral litmus solution. Add to
each an equal amount—a few threads—of well-washed fibrin which has been
previously steeped for some time in dilute hydrochloric acid, so that
it is swollen and transparent. Keep the tubes in a water-bath at about
104° Fahrenheit for an hour and examine them at intervals of twenty
minutes.
After five to ten minutes the fibrin in _A_ is dissolved and the
fluid begins to be turbid. In _B_ and _C_ there is no change. Even
after long exposure to 100° Fahrenheit there is no change in _B_
and _C_.
After a variable time, from one to four hours, the contents of the
stomach, which are now called chyme, begin to move on in successive
portions into the next part of the intestinal canal. The ring-like
muscles of the pylorus relax at intervals to allow the muscles of the
stomach to force the partly digested mass into the small intestines.
This action is frequently repeated, until even the indigestible masses
which the gastric juice cannot break down are crowded out of the
stomach into the intestines. From three to four hours after a meal the
stomach is again quite emptied.
A certain amount of this semi-liquid mass, especially the peptones,
with any saccharine fluids, resulting from the partial conversion of
starch or otherwise, is at once absorbed, making its way through the
delicate vessels of the stomach into the blood current, which is
flowing through the gastric veins to the portal vein of the liver.
Illustration: Fig. 55.—A Small Portion of the Mucous Membrane of the
Small Intestine. (Villi are seen surrounded with the openings of the
tubular glands.) [Magnified 20 diameters.]
143. The Small Intestine. At the pyloric end of the stomach the
alimentary canal becomes again a slender tube called the small
intestine. This is about twenty feet long and one inch in diameter, and
is divided, for the convenience of description, into three parts.
The first 12 inches is called the duodenum. Into this portion opens the
bile duct from the liver with the duct from the pancreas, these having
been first united and then entering the intestine as a common duct.
The next portion of the intestine is called the jejunum, because it is
usually empty after death.
The remaining portion is named the ileum, because of the many folds
into which it is thrown. It is the longest part of the small intestine,
and terminates in the right iliac region, opening into the large
intestine. This opening is guarded by the folds of the membrane forming
the ileo-cæcal valve, which permits the passage of material from the
small to the large intestine, but prevents its backward movement.
144. The Coats of the Small Intestine. Like the stomach, the small
intestine has four coats, the serous, muscular, sub-mucous, and mucous.
The serous is the peritoneum.[22] The muscular consists of an outer
layer of longitudinal, and an inner layer of circular fibers, by
contraction of which the food is forced along the bowel. The sub-mucous
coat is made up of a loose layer of tissue in which the blood-vessels
and nerves are distributed. The inner, or mucous, surface has a fine,
velvety feeling, due to a countless number of tiny, thread-like
projections, called villi. They stand up somewhat like the “pile” of
velvet. It is through these villi that the digested food passes into
the blood.
Illustration: Fig. 56.—Sectional View of Intestinal Villi. (Black dots
represent the glandular openings.)
The inner coat of a large part of the small intestine is thrown into
numerous transverse folds called _valvulæ conniventes_. These seem to
serve two purposes, to increase the extent of the surface of the bowels
and to delay mechanically the progress of the intestinal contents.
Buried in the mucous layer throughout the length, both of the small and
large intestines, are other glands which secrete intestinal fluids.
Thus, in the lower part of the ileum there are numerous glands in oval
patches known as _Peyer’s patches_. These are very prone to become
inflamed and to ulcerate during the course of typhoid fever.
145. The Large Intestine. The large intestine begins in the right iliac
region and is about five or six feet long. It is much larger than the
small intestine, joining it obliquely at short distance from its end. A
blind pouch, or dilated pocket is thus formed at the place of junction,
called the cæcum. A valvular arrangement called the ileo-cæcal valve,
which is provided with a button-hole slit, forms a kind of movable
partition between this part of the large intestine and the small
intestine.
Illustration: Fig. 57.—Tubular Glands of the Small Intestines.
A, B, tubular glands seen in vertical section with their orifices at C,
opening upon the membrane between the villi, D, villus (Magnified 40
diameters)
Attached to the cæcum is a worm-shaped tube, about the size of a lead
pencil, and from three to four inches long, called the _vermiform
appendix_. Its use is unknown. This tube is of great surgical
importance, from the fact that it is subject to severe inflammation,
often resulting in an internal abscess, which is always dangerous and
may prove fatal. Inflammation of the appendix is known as
_appendicitis_,—a name quite familiar on account of the many surgical
operations performed of late years for its relief.
The large intestine passes upwards on the right side as the ascending
colon, until the under side of the liver is reached, where it passes to
the left side, as the transverse colon, below the stomach. It there
turns downward, as the descending colon, and making an S-shaped curve,
ends in the rectum. Thus the large intestine encircles, in the form of
a horseshoe, the convoluted mass of small intestines.
Like the small intestine, the large has four coats. The mucous coat,
however, has no folds, or villi, but numerous closely set glands, like
some of those of the small intestine. The longitudinal muscular fibers
of the large intestine are arranged in three bands, or bundles, which,
being shorter than the canal itself, produce a series of bulgings or
pouches in its walls. This sacculation of the large bowel is supposed
to be designed for delaying the onward flow of its contents, thus
allowing more time for the absorption of the liquid material. The
blood-vessels and nerves of this part of the digestive canal are very
numerous, and are derived from the same sources as those of the small
intestine.
146. The Liver. The liver is a part of the digestive apparatus, since
it forms the bile, one of the digestive fluids. It is a large
reddish-brown organ, situated just below the diaphragm, and on the
right side. The liver is the largest gland in the body, and weighs from
50 to 60 ounces. It consists of two lobes, the right and the left, the
right being much the larger. The upper, convex surface of the liver is
very smooth and even; but the under surface is irregular, broken by the
entrance and exit of the various vessels which belong to the organ. It
is held in its place by five ligaments, four of which are formed by
double folds of the peritoneum.
The thin front edge of the liver reaches just below the bony edge of
the ribs; but the dome-shaped diaphragm rises slightly in a horizontal
position, and the liver passes up and is almost wholly covered by the
ribs. In tight lacing, the liver is often forced downward out from the
cover of the ribs, and thus becomes permanently displaced. As a result,
other organs in the abdomen and pelvis are crowded together, and also
become displaced.
147. Minute Structure of the Liver. When a small piece of the liver is
examined under a microscope it is found to be made up of masses of
many-sided cells, each about 1/1000 of an inch in diameter. Each group
of cells is called a _lobule_. When a single lobule is examined under
the microscope it appears to be of an irregular, circular shape, with
its cells arranged in rows, radiating from the center to the
circumference. Minute, hair-like channels separate the cells one from
another, and unite in one main duct leading from the lobule. It is the
lobules which give to the liver its coarse, granular appearance, when
torn across.
Illustration: Fig. 58.—Diagrammatic Section of a Villus
A, layer of columnar epithelium covering the villus;
B, central lacteal of villus;
C, unstriped muscular fibers;
D, goblet cell
Now there is a large vessel called the portal vein that brings to the
liver blood full of nourishing material obtained from the stomach and
intestines. On entering the liver this great vein conducts itself as if
it were an artery. It divides and subdivides into smaller and smaller
branches, until, in the form of the tiniest vessels, called
capillaries, it passes inward among the cells to the very center of the
hepatic lobules.
148. The Bile. We have in the liver, on a grand scale, exactly the same
conditions as obtain in the smaller and simpler glands. The thin-walled
liver cells take from the blood certain materials which they elaborate
into an important digestive fluid, called the bile.[23] This newly
manufactured fluid is carried away in little canals, called _bile
ducts_. These minute ducts gradually unite and form at last one main
duct, which carries the bile from the liver. This is known as the
hepatic duct. It passes out on the under side of the liver, and as it
approaches the intestine, it meets at an acute angle the cystic duct
which proceeds from the gall bladder and forms with it the common bile
duct. The common duct opens obliquely into the horseshoe bend of the
duodenum.
The cystic duct leads back to the under surface of the liver, where it
expands into a sac capable of holding about two ounces of fluid, and is
known as the gall bladder. Thus the bile, prepared in the depths of the
liver by the liver cells, is carried away by the bile ducts, and may
pass directly into the intestines to mix with the food. If, however,
digestion is not going on, the mouth of the bile duct is closed, and in
that case the bile is carried by the cystic duct to the gall bladder.
Here it remains until such time as it is needed.
149. Blood Supply of the Liver. We must not forget that the liver
itself, being a large and important organ, requires constant
nourishment for the work assigned to it. The blood which is brought to
it by the portal vein, being venous, is not fit to nourish it. The work
is done by the arterial blood brought to it by a great branch direct
from the aorta, known as the hepatic artery, minute branches of which
in the form of capillaries, spread themselves around the hepatic
lobules.
The blood, having done its work and now laden with impurities, is
picked up by minute veinlets, which unite again and again till they at
last form one great trunk called the hepatic vein. This carries the
impure blood from the liver, and finally empties it into one of the
large veins of the body.
After the blood has been robbed of its bile-making materials, it is
collected by the veinlets that surround the lobules, and finds its way
with other venous blood into the hepatic vein. In brief, blood is
brought to the liver and distributed through its substance by two
distinct channels,—the portal vein and the hepatic artery, but it
leaves the liver by one distinct channel,—the hepatic vein.
Illustration: Fig. 59.—Showing the Relations of the Duodenum and Other
Intestinal Organs. (A portion of the stomach has been cut away.)
150. Functions of the Liver. We have thus far studied the liver only as
an organ of secretion, whose work is to elaborate bile for future use
in the process of digestion. This is, however, only one of its
functions, and perhaps not the most important. In fact, the functions
of the liver are not single, but several. The bile is not wholly a
digestive fluid, but it contains, also, materials which are separated
from the blood to be cast out of the body before they work mischief.
Thus, the liver ranks above all others as an organ of excretion, that
is, it separates material of no further use to the body.
Of the various ingredients of the bile, only the bile salts are of use
in the work of digestion, for they act upon the fats in the alimentary
canal, and aid somehow in their emulsion and absorption. They appear to
be themselves split up into other substances, and absorbed with the
dissolved fats into the blood stream again.
The third function of the liver is very different from those already
described. It is found that the liver of an animal well and regularly
fed, when examined soon after death, contains a quantity of a
carbohydrate substance not unlike starch. This substance, extracted in
the form of a white powder, is really an animal starch. It is called
glycogen, or liver sugar, and is easily converted into grape sugar.
The hepatic cells appear to manufacture this glycogen and to store it
up from the food brought by the portal blood. It is also thought the
glycogen thus deposited and stored up in the liver is little by little
changed into sugar. Then, as it is wanted, the liver disposes of this
stored-up material, by pouring it, in a state of solution, into the
hepatic vein. It is thus steadily carried to the tissues, as their
needs demand, to supply them with material to be transformed into heat
and energy.
151. The Pancreas. The pancreas, or sweetbread, is much smaller than
the liver. It is a tongue-like mass from six to eight inches long,
weighing from three to four ounces, and is often compared in appearance
to a dog’s tongue. It is somewhat the shape of a hammer with the handle
running to a point.
The pancreas lies behind the stomach, across the body, from right to
left, with its large head embraced in the horseshoe bend of the
duodenum. It closely resembles the salivary glands in structure, with
its main duct running from one end to the other. This duct at last
enters the duodenum in company with the common bile duct.
The pancreatic juice, the most powerful in the body, is clear, somewhat
viscid, fluid. It has a decided alkaline reaction and is not unlike
saliva in many respects. Combined with the bile, this juice acts upon
the large drops of fat which pass from the stomach into the duodenum
and emulsifies them. This process consists partly in producing a fine
subdivision of the particles of fat, called an emulsion, and partly in
a chemical decomposition by which a kind of soap is formed. In this way
the oils and fats are divided into particles sufficiently minute to
permit of their being absorbed into the blood.
Again, this most important digestive fluid produces on starch an action
similar to that of saliva, but much more powerful. During its short
stay in the mouth, very little starch is changed into sugar, and in the
stomach, as we have seen, the action of the saliva is arrested. Now,
the pancreatic juice takes up the work in the small intestine and
changes the greater part of the starch into sugar. Nor is this all, for
it also acts powerfully upon the proteids not acted upon in the
stomach, and changes them into peptones that do not differ materially
from those resulting from gastric digestion. The remarkable power which
the pancreatic juice possesses of acting on all the food-stuffs appears
to be due mainly to the presence of a specific element or ferment,
known as _trypsin_.
Experiment 60. _To show the action of pancreatic juice upon oils or
fats._ Put two grains of Fairchild’s extract of pancreas into a
four-ounce bottle. Add half a teaspoonful of warm water, and shake well
for a few minutes; then add a tablespoonful of cod liver oil; shake
vigorously.
A creamy, opaque mixture of the oil and water, called an emulsion,
will result. This will gradually separate upon standing, the
pancreatic extract settling in the water at the bottom. When shaken
it will again form an emulsion.
Experiment 61. _To show the action of pancreatic juice on starch_. Put
two tablespoonfuls of _smooth_ starch paste into a goblet, and while
still so warm as just to be borne by the mouth, stir into it two grains
of the extract of pancreas. The starch paste will rapidly become
thinner, and gradually change into soluble starch, in a perfectly fluid
solution. Within a few minutes some of the starch is converted through
intermediary stages into maltose. Use the Fehling test for sugar.
152. Digestion in the Small Intestines. After digestion in the stomach
has been going on for some time, successive portions of the
semi-digested food begin to pass into the duodenum. The pancreas now
takes on new activity, and a copious flow of pancreatic juice is poured
along its duct into the intestines. As the food is pushed along over
the common opening of the bile and pancreatic ducts, a great quantity
of bile from this reservoir, the gall bladder, is poured into the
intestines. These two digestive fluids are now mixed with the chyme,
and act upon it in the remarkable manner just described.
Illustration: Fig. 60.—Diagrammatic Scheme of Intestinal Absorption.
A, mesentery;
B, lacteals and mesentery glands;
C, veins of intestines;
R.C, receptacle of the chyle (receptaculum chyli);
P V, portal vein;
H V, hepatic veins;
S.V.C, superior vena cava;
R.A, right auricle of the heart;
I.V.C, inferior vena cava.
The inner surface of the small intestine also secretes a liquid called
intestinal juice, the precise functions of which are not known. The
chyme, thus acted upon by the different digestive fluids, resembles a
thick cream, and is now called chyle. The chyle is propelled along the
intestine by the worm-like contractions of its muscular walls. A
function of the bile, not yet mentioned, is to stimulate these
movements, and at the same time by its antiseptic properties to prevent
putrefaction of the contents of the intestine.
153. Digestion in the Large Intestines. Digestion does not occur to any
great extent in the large intestines. The food enters this portion of
the digestive canal through the ileo-cæcal valve, and travels through
it slowly. Time is thus given for the fluid materials to be taken up by
the blood-vessels of the mucous membrane. The remains of the food now
become less fluid, and consist of undigested matter which has escaped
the action of the several digestive juices, or withstood their
influence. Driven onward by the contractions of the muscular walls, the
refuse materials at last reach the rectum, from which they are
voluntarily expelled from the body.
Absorption.
154. Absorption. While food remains within the alimentary canal it is
as much outside of the body, so far as nutrition is concerned, as if it
had never been taken inside. To be of any service the food must enter
the blood; it must be absorbed. The efficient agents in absorption are
the blood-vessels, the lacteals, and the lymphatics. The process
through which the nutritious material is fitted to enter the blood, is
called absorption. It is a process not confined, as we shall see,
simply to the alimentary canal, but one that is going on in every
tissue.
The vessels by which the process of absorption is carried on are called
absorbents. The story, briefly told, is this: certain food materials
that have been prepared to enter the blood, filter through the mucous
membrane of the intestinal canal, and also the thin walls of minute
blood-vessels and lymphatics, and are carried by these to larger
vessels, and at last reach the heart, thence to be distributed to the
tissues.
155. Absorption from the Mouth and Stomach. The lining of the mouth and
œsophagus is not well adapted for absorption. That this does occur is
shown by the fact that certain poisonous chemicals, like cyanide of
potash, if kept in the mouth for a few moments will cause death. While
we are chewing and swallowing our food, no doubt a certain amount of
water and common salt, together with sugar which has been changed from
starch by the action of the saliva, gains entrance to the blood.
In the stomach, however, absorption takes place with great activity.
The semi-liquid food is separated from the enormous supply of
blood-vessels in the mucous membrane only by a thin porous partition.
There is, therefore, nothing to prevent the exchange taking place
between the blood and the food. Water, along with any substances in the
food that have become dissolved, will pass through the partition and
enter the blood-current. Thus it is that a certain amount of starch
that has been changed into sugar, of salts in solution, of proteids
converted into peptones, is taken up directly by the blood-vessels of
the stomach.
156. Absorption by the Intestines. Absorption by the intestines is a
most active and complicated process. The stomach is really an organ
more for the digestion than the absorption of food, while the small
intestines are especially constructed for absorption. In fact, the
greatest part of absorption is accomplished by the small intestines.
They have not only a very large area of absorbing surface, but also
structures especially adapted to do this work.
157. The Lacteals. We have learned in Section 144 that the mucous
lining of the small intestines is crowded with millions of little
appendages called villi, meaning “tufts of hair.” These are only about
1/30 of an inch long, and a dime will cover more than five hundred of
them. Each villus contains a loop of blood-vessels, and another vessel,
the lacteal, so called from the Latin word _lac_, milk, because of the
milky appearance of the fluid it contains. The villi are adapted
especially for the absorption of fat. They dip like the tiniest fingers
into the chyle, and the minute particles of fat pass through their
cellular covering and gain entrance to the lacteals. The milky material
sucked up by the lacteals is not in a proper condition to be poured at
once into the blood current. It is, as it were, in too crude a state,
and needs some special preparation.
The intestines are suspended to the posterior wall of the abdomen by a
double fold of peritoneum called the mesentery. In this membrane are
some 150 glands about the size of an almond, called mesenteric glands.
Now the lacteals join these glands and pour in their fluid contents to
undergo some important changes. It is not unlikely that the mesenteric
glands may intercept, like a filter, material which, if allowed to
enter the blood, would disturb the whole body. Thus, while the glands
might suffer, the rest of the body might escape. This may account for
the fact that these glands and the lymphatics may be easily irritated
and inflamed, thus becoming enlarged and sensitive, as often occurs in
the axilla.
Having been acted upon by the mesenteric glands, and passed through
them, the chyle flows onward until it is poured into a dilated
reservoir for the chyle, known as the receptaculum chyli. This is a
sac-like expansion of the lower end of the thoracic duct. Into this
receptacle, situated at the level of the upper lumbar vertebræ, in
front of the spinal column, are poured, not only the contents of the
lacteals, but also of the lymphatic vessels of the lower limbs.
158. The Thoracic Duct. This duct is a tube from fifteen to eighteen
inches long, which passes upwards in front of the spine to reach the
base of the neck, where it opens at the junction of the great veins of
the left side of the head with those of the left arm. Thus the thoracic
duct acts as a kind of feeding pipe to carry along the nutritive
material obtained from the food and to pour it into the blood current.
It is to be remembered that the lacteals are in reality lymphatics—the
lymphatics of the intestines.
Illustration: Fig. 61.—Section of a Lymphatic Gland.
A, strong fibrous capsule sending partitions into the gland;
B, partitions between the follicles or pouches of the _cortical_ or
outer portion;
C, partitions of the _medullary_ or central portion;
D, E, masses of protoplasmic matter in the pouches of the gland;
F, lymph-vessels which bring lymph _to_ the gland, passing into its
center;
G, confluence of those leading to the efferent vessel;
H, vessel which carries the lymph away _from_ the gland.
159. The Lymphatics. In nearly every tissue and organ of the body there
is a marvelous network of vessels, precisely like the lacteals, called
the lymphatics. These are busily at work taking up and making over anew
waste fluids or surplus materials derived from the blood and tissues
generally. It is estimated that the quantity of fluid picked up from
the tissues by the lymphatics and restored daily to the circulation is
equal to the bulk of the blood in the body. The lymphatics seem to
start out from the part in which they are found, like the rootlets of a
plant in the soil. They carry a turbid, slightly yellowish fluid,
called lymph, very much like blood without the red corpuscles.