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Hygienic Physiology

J >> Joel Dorman Steele >> Hygienic Physiology




DIGESTION AND FOOD.

WHY WE NEED FOOD.--We have learned that our bodies are constantly giving
off waste matter--the products of the fire, or oxidation, as the chemist
terms the change going on within us (Note, p. 107). A man without food
will starve to death in a few days, _i. e._, the oxygen will have
consumed all the available flesh of his body. [Footnote: The stories
current in the newspapers of persons who live for years without food, are,
of course, untrue. The case of the Welsh Fasting Girl, which excited
general interest throughout Great Britain, and was extensively copied in
our own press, is in point. She had succeeded in deceiving not only the
public, but, as some claim, her own parents. At last a strict watch was
set by day and night, precluding the possibility of her receiving any food
except at the hands of the committee, from whom she steadily refused it.
In a few days she died from actual starvation. The youth of the girl, the
apparent honesty of the parents, and the tragical sequel, make it one of
the most remarkable cases of the kind on record.] To replace the daily
outgo, we need about two and a quarter pounds of food, and three pints of
drink. [Footnote: Every cell in the tissues is full of matter ready to set
free at call its stored-up energy--derived from the meat, bread, and
vegetables we have eaten. This energy will pass off quietly when the
organs are in comparative rest, but violently when the muscles contract
with force. When we send an order through a nerve to any part of the body,
a series of tiny explosions run the entire length of the nerve, just as
fire runs through a train of gunpowder. The muscle receives the stimulus,
and, contracting, liberates its energy. The cells of nerve or muscle,
whose contents have thus exploded, as it were, are useless, and must be
carried off by the blood, just as ashes must be swept from the hearth, and
new fuel be supplied to keep up a fire.]

Including the eight hundred pounds of oxygen taken from the air, a man
uses in a year about a ton and a half of material. [Footnote: The
following is the daily ration of a United States soldier. It is said to be
the most generous in the world:

Bread or flour . . . . . . . . . 22 ounces.
Fresh or salt beef (or pork or bacon, 12 oz.) . 20 "
Potatoes (three times per week) . . . . . 16 "
Rice . . . . . . . . . . . 1.6 "
Coffee (or tea, 0.24 oz.) . . . . . . 1.6 "
Sugar . . . . . . . . . . . 2.4 "
Beans . . . . . . . . . . . 0.64 gill.
Vinegar . . . . . . . . . . 0.32 "
Salt . . . . . . . . . . . . 0.16 "]

Yet during this entire time his weight may have been nearly uniform.
[Footnote: If, however, he were kept on the scale pan of a sensitive
balance, he would find that his weight is constantly changing, increasing
with each meal, and then gradually decreasing.] Our bodies are but molds,
in which a certain quantity of matter, checked for a time on its ceaseless
round, receives a definite form. They may be likened, says Huxley, to an
eddy in the river, which retains its shape for a while, yet every instant
each particle of water is changing.

WHAT FOOD DOES.--We make no force ourselves. We can only use that which
nature provides for us. [Footnote: We draw from Nature at once our
substance, and the force by which we operate upon her; being, so far,
parts of her great system, immersed in it for a short time and to a small
extent. Enfolding us, as it were, within her arms, Nature lends us her
forces to expend; we receive them, and pass them on, giving them the
impress of our will, and bending them to our designs, for a little while;
and then--Yes; then it is all one. The great procession pauses not, nor
flags a moment, for our fall. The powers which Nature lent to us she
resumes to herself, or lends, it may be, to another; the use which we have
made of them, or might have made and did not, is written in her book
forever.--_Health and its Conditions_.] All our strength comes from
the food we eat. Food is force--that is, it contains a latent power which
it gives up when it is decomposed. [Footnote: This force is chemical
affinity. It binds together the molecules which compose the food we eat.
When oxygen tears the molecules to pieces and makes them up into smaller
ones, the force is set free. As we shall learn in Physics, it can be
turned, into heat, muscular motion, electricity, etc. The principle that
the different kinds of force can be changed into one another without loss,
is called the Conservation of Energy, and is one of the grandest
discoveries of modern science.--_Popular Physics_, pages 35, 39,
278.] Oxygen is the magic key which unlocks for our use this hidden store.
[Footnote: We have spoken of the mystery that envelops the process of the
conversion of food force into muscular force (note, p. 107). All
physiologists agree that muscular power has its source in the chemical
decomposition of certain substances whereby their potential energy is
released. Probably some of the food undergoes this chemical change before
it passes out of the alimentary canal; possibly some is broken up by the
oxygen while it is being swept along by the blood; but, probably by far
the largest part is converted into the various tissues of the body, and
finally becomes a waste product only after there takes place in the tissue
itself that chemical disorganization that sets free its stored-up power.--
FOSTER'S _Physiology_.] Putting food into our bodies is like placing
a tense spring within a watch; every motion of the body is only a new
direction given to this food force, as every movement of the hand on the
dial is but the manifestation of the power of the bent spring in the
watch. We use the pent-up energies of meat, bread, and vegetables which
are placed at our service, and transfer them to a higher theater of
action. [Footnote: It is a grand thought that we can thus transform what
is common and gross into the refined and spiritual; that out of waving
wheat, wasting flesh, running water, and dead minerals, we can realize the
glorious possibilities of human life.]

KINDS OF FOOD NEEDED.--From what has been said it is clear that, in order
to produce heat and force, we need something that will burn, _i. e._,
with which oxygen can combine. Experiment has proved that to build up
every organ, and keep the body in the best condition, we require three
kinds of food.

1. _Nitrogenous Food_.--As nitrogen is a prominent constituent of the
tissues of the body, food which contains it is therefore necessary to
their growth and repair. [Footnote: Since this kind of food closely
resembles albumen, it is sometimes called _Albuminous_. The term
Proteid is also used.] The most common forms are whites of eggs--which are
nearly pure albumen; casein--the chief constituent of cheese; lean meat;
and gluten--the viscid substance which gives tenacity to dough. Bodies
having a great deal of nitrogen readily oxidize. Hence the peculiar
character of the quick-changing, force-exciting muscle.

2. _Carbonaceous Food_--_i. e._, food containing much carbon--
consists of two kinds, viz., the _sugars_, and the _fats_.

(1) The _sugars_ contain hydrogen and oxygen in the proportion to
form water, and about the same amount of carbon. They may, therefore, be
considered as water, with carbon diffused through it. In digestion, starch
and gum are changed to sugar, and so are ranked with this class.

(2) The _fats_ are like the sugars in composition, but contain less
oxygen, and not in the proportion to form water. They combine with more
oxygen in burning, and so give off more heat.

The non-nitrogenous elements of the food have, however, other uses than to
develop heat. [Footnote: The heat they produce in burning may be turned
into motion of the muscles, according to the principle of the Conservation
of Energy (p. 153, note); while all the structures of the body in their
oxidation develop heat.] Fat is essential to the assimilation of the food,
while sugar and starch aid in digestion and may be converted into fat.
[Footnote: In Turkey, the ladies of the harem are fed on honey and thick
gruel, to make flesh, which is considered to enhance their beauty. The
negroes on the sugar plantations of the South always grow fat during the
sugar-making season.] Fat and carbonaceous material both enter into the
composition of the various tissues, and when, by the breaking up of the
contractile substance of the muscle, their latent energy is set free, they
become the source of muscular force, as well as heat. While the tendency
of the albuminous food is to excite chemical action, and hence the release
of energy, the fats and carbonaceous food may be laid up in the body to
serve as a storehouse of energy to supply future needs.

3. _Mineral Matters_.--Food should contain water, and certain common
minerals, such as iron, [Footnote: While the body can build up a solid
from liquid materials on the one hand, on the other it can pour iron
through its veins and reduce the hardest textures to blood.--HINTON.]
sulphur, magnesia, phosphorus, salt, and potash. About three pints of
water are needed daily to dissolve the food and carry it through the
circulation, to float off waste matter, to lubricate the tissues, and by
evaporation to cool the system (see p. 317). It also enters largely into
the composition of the body. A man weighing one hundred and fifty-four
pounds contains one hundred pounds of water, about twelve gallons--enough,
if rightly arranged, to drown him. [Footnote: It is said that Blumenbach
had a perfect mummy of an adult Teneriffian, which with the viscera
weighed only seven and a half pounds.]

Iron goes to the blood disks; lime combines with phosphoric and carbonic
acids to give solidity to the bones and teeth; phosphorus is essential to
the activity of the brain. Salt is necessary to the secretion of some of
the digestive fluids, and also to aid in working off from the system its
waste products. These various minerals, except iron--sometimes given as a
medicine, and salt--universally used as a condiment, [Footnote: Animals
will travel long distances to obtain salt. Men will barter gold for it;
indeed, among the Gallas and on the coast of Sierra Leone, brothers will
sell their sisters, husbands their wives, and parents their children for
salt. In the district of Accra, on the gold coast of Africa, a handful of
salt is the most valuable thing upon earth after gold, and will purchase a
slave. Mungo Park tells us that with the Mandingoes and Bambaras the use
of salt is such a luxury that to say of a man "he flavors his food with
salt," it is to imply that he is rich; and children will suck a piece of
rock salt as if it were sugar. No stronger mark of respect or affection
can be shown in Muscovy, than the sending of salt from the tables of the
rich to their poorer friends. In the book of Leviticus it is expressly
commanded as one of the ordinances of Moses, that every oblation of meat
upon the altar shall be seasoned with salt, without lacking; and hence it
is called the Salt of the Covenant of God. The Greeks and Romans also used
salt in their sacrificial cakes; and it is still used in the services of
the Latin church--the "_parva mica_" or pinch of salt, being in the
ceremony of baptism, put into the child's mouth, while the priest says,
"Receive the salt of wisdom, and may it be a propitiation to thee for
eternal life." Everywhere and almost always, indeed, it has been regarded
as emblematical of wisdom, wit, and immortality. To taste a man's salt,
was to be bound by the rites of hospitality; and no oath was more solemn
than that which was sworn upon bread and salt. To sprinkle the meat with
salt was to drive away the devil, and to this day, nothing is more unlucky
than to spill the salt.--LETHEBY, _On Food_.] are contained in
small, but sufficient quantities in meat, bread, and vegetables.

ONE KIND OF FOOD IS INSUFFICIENT.--A person fed on starch alone, would
die. It would be a clear case of nitrogen starvation. On the other hand,
as nitrogenous food contains carbon, the elements of water, and various
mineral matters, life could be supported on that alone. But such a
prodigious quantity of lean meat, for example, would be required to
furnish the other elements, that not only would it be very expensive, but
it is likely that after a time the labor of digestion would be too
onerous, and the system would give up the task in despair. The need of a
diet containing both nitrogenous and carbonaceous elements is shown in the
fact that even in the tropical regions oil is relished as a dressing upon
salad. Instinct everywhere suggests the blending. Butter is used with
bread; rice is boiled with milk; cheese is eaten with macaroni, and beans
are baked with pork.

FIG. 45.

[Illustration: _The Stomach and Intestines._ 1, _stomach;_ 2,
_duodenum;_ 3, _small intestine;_ 4, _termination of the
ileum;_ 5, _cœcum;_ 6, _vermiforn appendix;_ 7, _ascending
colon;_ 8, _transverse colon;_ 9, _descending colon;_ 10,
_sigmoid flexure of the colon;_ 11, _rectum;_ 12, _spleen--a
gland whose action is not understood._--LEIDY'S _Anatomy._]

THE OBJECT OF DIGESTION.--If our food were cast directly into the blood,
it could not be used. For example, although the chemist can not see
wherein the albumen of the egg differs from the albumen of the blood, yet
if it be injected into the veins it is unavailable for the purposes
required, and is thrown out again. In the course of digestion the food is
modified in various ways whereby it is fitted for the use of the body,
into which it is finally incorporated. We call this change of food into
flesh _assimilation_, a name for a work done solely by the vital
organs, and so mysterious in its nature that the wisest physiologist gets
only glimpses here and there of its operations.

THE GENERAL PLAN OF DIGESTION.--Nature has provided for this purpose an
entire laboratory, furnished with a chemist's outfit of knives, mortars,
baths, chemicals, filters, etc. The food is (1) chewed, mixed with the
saliva in the mouth, and swallowed; (2) it is acted upon by the gastric
juice in the stomach; (3) it is passed into the intestines, where it
receives the bile, pancreatic juice, and other liquids which completely
dissolve it; [Footnote: Digestion, says Berzelius, is a process of
rinsing. The digestive apparatus secretes, and again absorbs with the food
which it has dissolved, not less than three gallons of liquid per day.--
BARNARD, BIDDER, SCHMIDT, and others.] (4) the nourishing part is absorbed
in the stomach and intestines, and thence thrown into the blood vessels,
whence it is whirled through the body by the torrent of the circulation.
These processes take place within the _alimentary canal_, a narrow
tortuous tube which commences at the mouth, and is about thirty feet long.
[Footnote: The digestive apparatus is lined with mucous membrane that
possesses functions similar to those of the outer skin. It absorbs certain
substances and rejects waste matter. On account of this close connection
between the inner and the outer skin, it is not surprising to find that in
the lowest animals digestion is performed by means of the external skin.
The amœba, which is merely a gelatinous mass, when it takes its food,
extemporizes a stomach for the occasion. It simply wraps itself around the
morsel, and, like an animated apple dumpling with the apple for food and
the crust for animal, goes on with the process until the operation is
completed, when it unrolls itself again and lets the indigestible residue
escape. The common hydra of our brooks can live when turned inside out,
like a glove; either side serving for skin or stomach, as necessity
requires.]

FIG. 46.

[Illustration: _The Parotid--one of the salivary glands._]

I. MASTICATION AND INSALIVATION.--l. _The Saliva_.--The food while
being cut and ground by the teeth is mixed with the saliva. This is a
thin, colorless, frothy, slightly alkaline liquid, secreted [Footnote: By
secretion is meant merely a separation or picking out from the blood.] by
the mucous membrane lining the mouth, and by three pairs of salivary
glands (parotid, submaxillary, and sublingual) opening into the mouth
through ducts, or tubes. The amount varies, but on the average is about
three pounds per day, and in health is always sufficient to keep the mouth
moist. [Footnote: The presence and often the thought of food will "make
one's mouth water." Fear checks the flow of saliva, and hence the East
Indians sometimes attempt to detect theft by making those who are
suspected chew rice. The person from whom it comes out driest is adjudged
the thief.] It softens and dissolves the food, and thus enables us to get
the flavor or taste of what we eat. It contains a peculiar organic
principle called _ptyalin_, [Footnote: One part of ptyalin will
convert eight thousand parts of starch into sugar.--MIALEE.

The saliva has no chemical action on the fats or the albuminous bodies.
Its frothiness enables it to carry oxygen into the stomach, and this is
thought to be of service. The action of the ptyalin commences with great
promptness, and sugar has been detected, it is said, within half a minute
after the starch was placed in the mouth. The process, however, is not
finished there, but continues after reaching the stomach.--VALENTIN. The
saliva thus prepares a small portion of food for absorption at once, and
so insures at the very beginning of the operation of digestion a supply of
force-producing material for the immediate use of the system.] which,
acting upon the starch of the food, changes it into glucose or grape
sugar.

2. _The Process of Swallowing._--The food thus finely pulverized,
softened, and so lubricated by the viscid saliva as to prevent friction as
it passes over the delicate membranes, is conveyed by the tongue and cheek
to the back of the mouth. The soft palate lifts to close the nasal
opening; the epiglottis shuts down, and along this bridge the food is
borne, without danger of falling into the windpipe or escaping into the
nose. The muscular bands of the throat now seize it and take it beyond our
control. The fibers of the œsophagus contract above, while they are lax
below, and convey the food by a worm-like motion into the stomach.
[Footnote: We can observe the peculiar motion of the œsophagus by watching
a horse's neck when he is drinking.]

II. GASTRIC DIGESTION.--1. _The Stomach_ is an irregular expansion of
the digestive tube. Its shape has been compared to that of a bagpipe. It
holds about three pints, though it is susceptible of some distension. It
is composed of an inner, mucous membrane, which secretes the digestive
fluids; an outer, smooth, well-lubricated serous one, which prevents
friction, and between them a stout, muscular coat. The last consists of
two principal layers of longitudinal and circular fibers. When these
contract, they produce a peculiar churning motion, called the
_peristaltic_ (_peri_, round; _stallein_, to arrange) movement, which
thoroughly mixes the contents of the stomach. At the farther end, the
muscular fibers contract and form a gateway, the _pylorus_ (a gate),
as it is called, which carefully guards the exit, and allows no food
to pass from the stomach until properly prepared. [Footnote: With a
wise discretion, however, it opens for buttons, coins, etc., swallowed
by accident; and when we overload the stomach, it seems to become weary of
constantly denying egress, and, finally, giving up in despair, lets
everything through.]

FIG. 47.

[Illustration: _Diagram of the Digestion of the Food. Notice how the
food is submitted to the action of alkaline, acid, and then alkaline
fluids. (See note, p._ 165.)]

2. _The Gastric Juice_.--The lining of the stomach is soft, velvety,
and of a pinkish hue; but, as soon as food is admitted, the blood vessels
fill, the surface becomes of a bright red, and soon there exudes from the
gastric glands a thin, colorless fluid--the gastric juice. (See p. 319.)
This is secreted to the amount of twelve pounds per day. [Footnote: The
amount secreted by a healthy adult is variously estimated from five to
thirty-seven pounds. As it is reabsorbed by the blood, there is no loss.]
Its acidity is probably due to muriatic or lactic acid--the acid of sour
milk. It contains a peculiar organic principle called _pepsin_
[Footnote: Pepsin is prepared and sold as an article of commerce. The best
is said to be made from the stomachs of young, healthy pigs, which, just
before being killed, are excited with savory food that they are not
allowed to eat. One grain is sufficient to dissolve eight hundred grains
of coagulated white of egg. A temperature of 130° renders pepsin inert.]
(_peptein_, to digest), which acts as a ferment to produce changes in
the food, without being itself modified.

The flow of gastric juice is influenced by various circumstances. Cold
water checks it for a time, and ice for a longer period. Anger, fatigue,
and anxiety delay and even suspend the secretion. The gastric juice has no
effect on the fats or the sugars of the food; its influence being mainly
confined to the albuminous bodies, which it so changes that they become
soluble in water. [Footnote: The question is often asked why the stomach
itself is not digested by the gastric juice, since it belongs to the
albuminous substances. Some have assigned as the probable reason that life
protects that organ, and assert that living tissues can not be digested;
but the fallacy of this has been clearly shown by experiments that have
been made with living tissues in the course of scientific research. The
latest opinion is that the blood which circulates so freely through the
vessels of the lining of the stomach, being alkaline, protects the tissue
against the acidity of the gastric juice.]

The food, reduced by the action of the gastric juice to a grayish, soupy
mass, called _chyme_ (kime), escapes through that jealously guarded
door, the pylorus.

Fig. 48.

[Illustration: _A vertical Section of the Duodenum, highly
magnified._ 1, _a fold-like villus;_ 2, epithelium, or cuticle;_
3, _orifices of intestinal glands;_ 5, _orifice of duodenal glands;_
4, 7, _more highly magnified sections of the cells of a duodenal gland._]

III. INTESTINAL DIGESTION--The structure of the intestines is like that
of the stomach. There is the same outer, smooth, serous membrane
(peritoneum) to prevent friction, the lining of mucous membrane to secrete
the digestive fluids, and the muscular coating to push the food forward.
The intestines are divided into the _small_ and the _large_. The
first part of the former opens out of the stomach, and is called the
_du-o-de'-num_, as its length is equal to the breadth of twelve
fingers. Here the chyme is acted upon by the _bile_, and the
_pancreatic juice_.

FIG. 49.

[Illustration: _The Mucous Membrane of the Ilium, highly magnified._
1, _cellular structure of the epithelium, or outer layer;_ 2, _a
vein;_ 3, _fibrous layer;_ 4, _villi covered with epithelium;_ 5,
_a villus in section, showing its lining of epithelium, with its
blood vessels and lymphatics;_ 6, _a villus partially uncovered;_
7, _a villus stripped of its epithelium;_ 8, _lymphatics or lacteals;_
9, _orifices of the glands opening between the villi;_ 10, 11, 12,
_glands;_ 13, _capillaries surrounding the orifices of the gland._]

1. _The Bile_ is secreted by the liver. This gland weighs about four
pounds, and is the largest in the body. It is located on the right side,
below the diaphragm. The bile is of a dark, golden color, and bitter
taste. About three pounds are secreted per day. When not needed for
digestion, it is stored in the gall cyst. [Footnote: A gall bladder can be
obtained from a butcher, and the contents kept in a bottle for
examination.] Its action on the food, though not fully understood, is
necessary to life. [Footnote: The bile is produced, unlike all the other
animal secretions, from venous blood; that is, the already contaminated
blood of the portal vein. Its complete suppression produces symptoms of
poisoning analogous to those which follow the stoppage of respiration, and
the patient dies, usually in a comatose condition, at the end of ten or
twelve days.--DALTON. The alkaline bile neutralizes the acid contents of
the stomach as they flow into the duodenum, and thus prepares the way for
the pancreatic juice. It has also a slight emulsifying power (note, p.
167).]

2. _The Pancreatic Juice_ is a secretion of the pancreas, or
"sweetbread"--a gland nearly as large as the hand, lying behind the
stomach. It is alkaline, and contains a ferment called _trypsin_.
This juice has the power of changing starch to sugar. Its main work,
however, is in breaking up the globules of fat into myriads of minute
particles, that mix freely with water, and remain suspended in it like
butter in new milk. The whole mass now assumes a milky look, whence it is
termed _chyle_ (kile) and passes on to the small intestine.
[Footnote: It is curious to observe that while the gastric juice is
decidedly acid, the fluids with which the food next comes into contact are
alkaline. It is thus submitted to the operation alternately of alkaline,
acid, and again of alkaline secretions. In the herbivora there is also a
second acid juice. The reason of these alternations is not known, but it
can hardly be doubted that they serve to make the digestion of the food
more perfect. And although the solvent power of the gastric juice is
placed in abeyance when its acidity is neutralized by the alkaline fluids,
yet it appears to be the case here, as in respect to the saliva, that
effects are produced by the mixture of the various secretions which are
poured together into the digestive tube, that would not result from either
alone.--HINTON.]

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