REPAIR AND ELIMINATION OF WASTE (METABOLISM)
The work of the body never stops. If it is to be kept in thorough
working order its tissues must be rebuilt as incessantly as they are
torn down in the process of producing heat and energy. These chemical
changes are called collectively _metabolism_.
They are divided into two groups: the chemical process of building
up complex substances from simple ones is known as _anabolism_; the
chemical process of oxidizing and breaking down the complex substances
into simple ones, so that they are in a state to be excreted, is called
_catabolism_. While the process of oxidation in catabolism is going on,
heat and energy are set free. Many of the chemical changes in the body
are catabolic in character. This work never ceases—even in sleep.
It is not enough that the proper foods be furnished the body in
kind and quantity. The essential thing is that the system be kept
in condition to _assimilate_ the foods to its needs and to promptly
eliminate the waste. Few people assimilate all of the foods eaten.
By _assimilation_ is meant the process by which foodstuffs are made
soluble and diffusible, so that they can pass into the blood; also,
the metabolic activity by which the food is converted into cells and
tissues.
Truly the body is a busy workshop. Think of the billions on billions
of cells being formed and destroyed every instant in the liberation of
heat and force! Think, also, of the necessity of perfect circulation to
bring sufficient blood to the lungs, that it may gather the oxygen and
carry it, without pausing for rest, to every tissue of the body! Even
in sleep this stream continues incessantly.
There is also a great lesson here in the law of supply and demand.
When the body is at mental or muscular work, the potential energy
liberated leaves through muscle or brain, as energy, and is expressed
in the result of the work. When the body is at rest, energy leaves it
as heat (excepting such part as is necessary to carry on metabolism,
circulation, etc.).
If much muscular energy is called for, a deep, full breath is
instinctively drawn to supply the oxygen necessary for the added force.
If strong mental work is required, attention should be given to
exercise and deep breathing, that the blood may carry off the waste
liberated by brain activity. The difficulty is that in doing close
mental work, the body is too frequently bent over a desk in such a
manner as to restrict the action of the lungs; thus, the brain worker,
in order to continue strong mental work, must often go into the open
air, as he says, “to rest his brain,” but in reality to obtain the
oxygen needed to put the waste, liberated by brain energy, in condition
to be carried away. The supply of blood has been called on for the
brain work; the poor circulation through the body has allowed an excess
of carbon dioxid to accumulate and the condition of the body designated
as “tired” has resulted. Until the necessary oxygen has been supplied,
the brain and body are not balanced, not “rested.”
In its conversion into tissue, heat, energy, and waste, the importance
of the chemical exceeds that of the mechanical action of digestion,
absorption, assimilation, and elimination; yet the chemical changes are
aided by the mechanical.
Nature provides against ignorance of the amount of supply necessary,
by enabling the system to carry off a limited amount of surplus food
above the bodily requirements. Her capacity in this regard is limited
and varies with each individual. Therefore common sense is required in
deciding for oneself the amount of food which will aid, and not hinder
Nature in her processes.
Without doubt many eat more food than the system requires, and when it
is overloaded they do not take the pains to burn up and eliminate the
excess through exercise and oxygen.
On the other hand, this theory of overeating has been so long
discussed that many have not eaten sufficient food and their bodies
are undernourished. Many, also, from lack of exercise, hence lack of
demand of the body for food, have supposed this lack of appetite to
be Nature’s call “Enough”; inertia has resulted and waste remains in
the body. They have failed to exercise sufficiently to create a demand
for food. It is thus undernourished because sufficient new building
material has not been supplied. The relief from this condition is
exercise and deep breathing so that Nature removes the waste and calls
for fresh building material.
Many others, through mental and physical activity, burn up much fuel
and the result is the body does not store up sufficient fat for a
reserve, or for beauty and comfort. The nerves require a certain amount
of fat for their protection. People of this type should take a more
full and sometimes a more varied diet, particularly more liquid, and
should not fail in daily exercise and deep breathing.
Each individual should know, approximately, the chemical constituents
and the proportion of these constituents in normal blood, because from
the elements in the blood, the tissues are constructed. If certain
elements are lacking, the foods containing these elements in largest
proportions should be supplied until the blood no longer shows the
deficiency. This is Nature’s method of correction. The variations in
the blood can be known only by chemical analyses and until physicians
have access to chemical laboratories the giving of drugs cannot be a
science.
Each meal, or each day’s food, may not contain the amount of protein or
of fuel ingredients necessary for that day’s work and resupply, but the
body is continually storing material, and this reserve is constantly
being drawn on to provide any element which may be lacking in that
day’s supply. Thus, an excess or a deficiency one day may be adjusted
the next. Healthful nourishment requires that the balance, as a whole,
be kept and that a deficiency or oversupply be not continued for too
long.
The distinct steps in anabolism and the effect of oxygen on
assimilation are discussed in the following pages.
_DIGESTION_
Any discussion of the digestibility of foods must be general, because
food which agrees with one may disagree with another, and a food which
disagrees with one at a particular time may entirely agree with him at
some other time according to the condition of his system. Therefore,
before one passes on the adaptability of a food to his system, he
should know that this food agrees or disagrees with him under various
conditions.
The chances are that the food is right but that the attitude of mind
and the condition of the body are abnormal.
The digestibility of food depends largely on the physical condition of
the individual, because the amount of digestive juices poured into the
alimentary canal is influenced by this condition, particularly by the
condition of the nerves. If sufficient juices, in proper proportions,
are not poured into the digestive tract, the foodstuffs are not made
soluble for absorption.
Digestion is practically synonymous with solution—all solid foods must
be reduced to a liquid state by means of the digestive juices and water
before they can pass through the walls of the stomach and intestines
and enter the blood.
Each individual should learn to like the foods containing the nutrient
elements which experience and blood tests have shown to be lacking in
his case.
Yet while it is true that in most cases the aversion to a particular
food is largely mental, there are kinds of food which, to certain
individuals, according to the chemical composition of the body, act as
actual poisons, _e. g._, strawberries, cheese, or coffee.
The question of likes and of dislikes in foods, is largely habit, and
one can learn to like almost any food, if one really has the desire to
do so.
When the habit has been formed of discriminating too much in the food,
of discarding this food or that, because at some time it has disagreed,
due to the particular condition at the time, the mind approaches the
table in a pessimistic attitude and the saliva and the gastric juices
are retarded in their flow.
When one is exercising freely, so that the muscular and mucous coats
of the digestive system are strong, the body will handle foods which,
during sedentary habits, it would not digest.
_Much indigestion is due to mental apathy. The mind often needs
arousing to an interest in something._
Such an individual needs to know that one of the hardest things for
the members of his family is to live day by day with one who maintains
an attitude of mental depression, and he should stir himself for “his
stomach’s sake,” as well as for the sake of his family, to a cheerful
interest in something. He should let go his grudge and ride a hobby, if
it is a cheerful one, and ride it hard.
It may be well, here, to trace, briefly, the progress of the food
through the digestive tract and the action of the juices and the
ferments on it.[5]
* * * * *
[Sidenote: Salivary Digestion]
The food in the mouth is mixed with saliva, which begins the
dissolution of the starches.
The saliva consists of about 99.5 per cent. water and 0.5 per
cent. solids. The solids consist of ptyalin, sodium chlorid, sodium
carbonate, mucus, and epithelium. Ptyalin, the most important of these,
is the active digestive agent; the mucus lubricates the masticated
food; the sodium carbonate insures the alkalinity of the food, and the
water dissolves the food that the juices may more readily reach and act
on each particle.
The starches are the only foods whose chemical digestion is begun in
the mouth. They are first broken up by the ptyalin into dextrin and
then into the more simple sugar, known as maltose.[6]
It is important that sufficient saliva be mixed with the food through
mastication, because unless the digestion of the starches is begun by
the saliva, either in the mouth or after it is swallowed, they are
not acted on until they reach the small intestine, consequently their
digestion is unduly delayed. The pancreatic juice must then do more
than its normal work of digestion.
The saliva flows into the mouth, more or less, at all times, but more
copiously during mastication.
The movement of the jaws in chewing incites its flow and when starches
are not well digested, gum chewing, in moderation, though not a refined
habit, is beneficial.
The evident purpose of the saliva when food is not present is to keep
the lining of the mouth moist.
Salivary digestion is carried on in the stomach until the food becomes
thoroughly mixed with the gastric juice, which, being acid, inhibits
the action of the ptyalin.
The thorough and regular cleansing of the teeth is an important aid to
digestion. Food products allowed to remain about the teeth ferment,
rendering the mouth acid. When the mouth is acid, the alkaline saliva
does not secrete in sufficient amount and the mouth is more or less dry.
The mouth is acid in rheumatism and allied conditions and the saliva
may be thick and ropy so that it does not moisten the food properly.
On the other hand the flow of saliva may be too free, the ptyalin is
then too much diluted to promptly act on the food. This may result from
overstimulation of the salivary glands occasioned by the excessive
chewing of gum, or tobacco. These excesses also carry too much air into
the stomach, resulting in flatulence.
The flow of saliva is controlled, largely, by nerves centering in the
medulla oblongata. The sight of food, pleasingly served, or even the
thought of food which one likes, will increase the flow. This is one
instance of the control of thought over digestion, and the importance
of forming the habit of cultivating a taste for all kinds of food is
apparent. The stronger the relish for the food, and the more thoroughly
it is masticated and mixed with the saliva, the more perfectly will the
first step in digestion be accomplished.
Thorough mastication is important, not only because the chemical action
on the starch molecules is facilitated by the softening and mixing with
the saliva, but also because thorough mastication tends to prevent
overeating—the appetite is more quickly satisfied when the food is well
masticated.
Cool water encourages the flow of saliva and for this reason should
be drunk before meals, particularly when digestion is weak. It may be
taken at rest periods during the meal. (See page 31.)
* * * * *
[Sidenote: The Mouth and Nasal Passages]
The relation of the mouth and nasal passages to the digestive processes
is seldom considered by the average individual. Their importance to the
growing child is being recognized by the examination of school children
which is now being made a part of the health program in many of our
cities. Their importance to the adult is no less.
Food particles allowed to remain around the teeth, or in the cavities
of decayed teeth, incite bacterial action. With the next meal these
bacteria are swallowed and cause fermentation of the food, occasioning
indigestion, and possibly, dyspepsia.
Decayed or missing teeth, swollen gums, or pyorrhea, interfere with
proper mastication of food, hence it does not receive the thorough
salivary moistening necessary; the starches pass practically unchanged
into the stomach and small intestine, overburdening these organs.
Catarrh of the nasal passages, with the constant swallowing of
germ-filled secretions, carries morbid products into the stomach,
coating the glands with mucus, often infecting them; it may also
occasion a catarrhal condition of that organ.
If, from any cause, the saliva becomes acid, dryness of the mouth
results and desire for food is lessened or absent. Diseases of the
salivary glands may render these necessary secretions unfit to perform
their work.
In illness the mouth often drops open from weakness, producing
the same condition of dryness. The mouth, in illness, is too often
neglected by those in charge of the invalid.
Adenoids and enlarged turbinates in child or adult, narrowing the nasal
passages and preventing the ingress of air, cause mouth breathing. The
air dries the membranes and the tongue becomes swollen and cracks,
interfering with proper mastication.
Adenoids should be removed, and any other condition which interferes
with the proper function of the mouth should be remedied as soon as
possible.
The mouth should be properly cleansed, the gums massaged, the teeth
thoroughly brushed, back as well as front, defective teeth repaired or
removed, abnormal growths eliminated, and the secretions kept abundant
and healthy. Food well prepared in the mouth by thorough mastication
satisfies hunger, renders more easy the work of the stomach and
intestines, and aids in the general welfare of the system.
* * * * *
[Sidenote: Gum-chewing]
This too prevalent habit may aggravate the condition which it is
supposed to cure. A slight indigestion appearing, gum is often chewed
to cause a fuller flow of saliva to aid digestion. If gum-chewing is
indulged in to excess, however, the muscular movements overstimulate
the salivary glands, eventually weakening them. Overuse of the chewing
muscles and overexcitation of the nerves fatigue them and cause them to
weaken. The sticky gum, adhering to fillings in the teeth, loosens them
and furnishes a lodging place for food particles and bacteria.
The excess of saliva may render the gastric juice alkaline, inhibiting
its action. Excess of air swallowed with the saliva may cause
flatulence or accumulation of gas in the stomach.
Lack of poise and nerve tension is increased by excessive gum-chewing,
resulting in fatigue of the entire body. This lack of poise may
be noted in any public assembly, as the “movies,” frequented by
gum-chewers.
The habit, as generally practiced, is not an inspiring sight and should
be discouraged.
Gum-chewing in moderation, for a few minutes after a meal, may not
do harm, but its indiscriminate use is to be deplored. Thorough
mastication of food will serve to supply the necessary saliva.
Exercise directed to the stomach and a more thorough circulation
and elimination will do more for any digestive derangement than the
excessive practice of chewing gum.
* * * * *
[Sidenote: Stomach Digestion]
As the food enters the stomach, the gastric juice pours out from the
mucous lining, very much as the saliva pours into the mouth. Like the
saliva, it consists of 99.5 per cent. water and 0.5 per cent. solids.
The solids of the gastric juice are pepsin, rennin, hydrochloric acid,
and mucus.
The _mucus_ serves to lubricate the food as in the saliva. It perhaps
also aids to prevent the digestion of the mucous lining of the stomach.
The _hydrochloric acid_ and the _pepsin_ cause the principal chemical
changes in the food while in the stomach. They act only on the
proteins. The hydrochloric acid must be present before the pepsin can
act, as only in an acid medium can pepsin dissolve the proteins. It is
also of an antiseptic nature and hinders or prevents the decomposition
of food.
The _rennin_ ferment precipitates the casein.
The only digestion of starches in the stomach is that continued by the
saliva.
Gastric juice begins to flow into the stomach soon after eating,
but normally it is not secreted in sufficient quantity to supersede
salivary digestion for from twenty to forty-five minutes.
The result of gastric digestion of proteins is their conversion, first,
into albumin, then into proteoses, and, lastly, into peptone, which is
protein in a more simple, soluble, and diffusible form. In the form of
peptone, the proteins are in condition to be absorbed.
If the food has been properly cooked and masticated, gastric digestion
will be completed in from one and one-half to three hours. If not
properly cooked and masticated, the stomach digestion may continue from
one to two hours longer. It should, however, be completed in three
hours.
It will be seen that the evening meal is ordinarily digested before
sleep, as one does not retire for from three to five hours after eating.
If, through imperfect mastication, or a disordered condition of the
stomach, the digestion is not completed in about three hours, the
food is likely to be retained in the stomach and by its weight may
cause prolapsus of that organ if the supporting tissues are weak.
Fermentation may ensue and give rise to gases which may cause acute
distress.
Animal foods, which are readily digested, remain in the stomach for
a shorter time. Meat, as a rule, is easily digested, because the
digestive juices of the animal have converted the starches and sugars.
The white meat of chicken is digested in a shorter time than the red
or the dark meat.
Corn, beets, peas, beans, etc., take about three and a half hours to
digest; baked potatoes about two and a half hours.
Raw vegetables and fruits remain about the same length of time as
potatoes.
Sugar is usually absorbed within an hour.
The cereals, if well cooked, take but two hours.
Coarse or badly masticated food, tough meats, unripe fruits, and much
fat hinder digestion.
Undigested food passing into the intestine may fail to be acted on
there and will sometimes produce diarrhea.
Fluids leave the stomach more rapidly than solids. Seven ounces of
water entirely leaves the stomach in one and one-half hours, seven
ounces of boiled milk in about two hours. Water and buttermilk almost
immediately begin to pass out of the stomach; milk begins to pass out
in about fifteen minutes.
The flow of gastric juice, as the flow of saliva, is governed by the
nerves; the sight, taste, and smell of food, and the attitude of mind
toward it, to a certain extent, regulate its flow.
After the food has accumulated, during the progress of a meal, the
stomach begins a series of wave-like movements called peristaltic
waves.[7] These waves propel the food through the length of the stomach
towards its lower opening, known as the pyloric orifice. During this
process the food is thoroughly mixed with the gastric juice.
During the early stages of digestion of solids, the sphincter muscles
of the pylorus keep the lower opening of the stomach closed, but,
as digestion progresses, the pylorus gradually relaxes to let the
digested, soluble portion of the food pass into the intestine. If the
food still remains in a solid form, by reason of being improperly
cooked or poorly masticated, as it touches the pylorus, these sphincter
muscles, almost as if they were endowed with reasoning faculties,
close, forcing the undigested mass back to be further acted on by the
gastric juice—the solid mass is not allowed to pass until dissolved.
If the individual abuses the stomach and causes it to work overtime, it
becomes exhausted and demands rest; it refuses to discharge the gastric
juice in proper proportion; the peristaltic movements are weak; and
food is not promptly or forcefully moved along the stomach and mixed
with the gastric juice. This condition is termed indigestion.
* * * * *
[Sidenote: Intestinal Digestion]
The food passes from the stomach, through the pylorus into the small
intestine. In this condition of partial digestion it is called chyme.
The first twelve inches of the small intestine is known as the
duodenum. In the duodenum the food is acted on by the pancreatic
juice, the bile, and the intestinal juices. These juices act on
proteins, fats, and carbohydrates. The bile acts on the fats, while
the pancreatic and intestinal juices act on the proteins and the
carbohydrates. The starches, or dextrin, not fully digested by the
saliva, are changed to maltose and glucose, while the trypsin from the
pancreatic juice, together with the intestinal juices, change into
peptone the protein not fully digested in the stomach. The pancreatic
juice also digests the starch found in raw fruits and in such raw
vegetables as radishes and lettuce.
Fats are almost entirely digested in the small intestine. The presence
of fat stimulates the flow of pancreatic juice, which, in turn,
stimulates the flow of bile. For this reason, in some conditions, if
the liver is sluggish, fatty foods in moderation are desirable. When
bile is not present in sufficient amount the fatty foods ferment and
cause gases and foul odors.
The fats are absorbed almost entirely in the small intestine—mostly
in the duodenum. Some of the fat may be absorbed directly without
undergoing the process of emulsification. Some oils, as paraffin oil,
are not absorbed at all but act only as a lubricant of the intestines.
When the food enters the intestine its reaction is acid. Mixed with
the bile, pancreatic and intestinal juices, which are alkaline, its
reaction becomes alkaline.
The pancreatic juice splits up the fats into glycerin and fatty acids
and enables the bile to exert its important emulsifying power. The bile
markedly aids this action of the pancreatic juice though it has no
fat-splitting power in itself.
Steapsin, another ferment of the pancreatic juice, acts on both fats
and carbohydrates in either an acid or alkaline medium.
The sodium in the bile unites with the fatty acid, forming a soap which
coats the tiny particles of fat and emulsifies them. The bile thus aids
in the absorption of the fats. It also lubricates the intestinal mass,
facilitating its passage through the entire length of the intestines.
Thus it is a very potent agent in regulating the bowel movements.
A diminution in the flow of bile quickly expresses itself in
constipation.
Fat and protein stimulate the activity of the liver, while starches, if
taken in excess, incline to overload it.
The food is forced along the intestinal tract by peristaltic or
muscular relaxation and contraction waves, as in the stomach. As it is
so forced, the nutrient elements, after being put into condition for
absorption, are taken up through the villi of the intestinal walls by
the portal veins and the lacteals of the submucous lining.
A larger proportion of food is digested and absorbed than was formerly
supposed, and the excretions from the intestines are, in many cases,
made up almost entirely of refuse, and of the catabolic waste of the
system. In an ordinary mixed diet, it is stated that about ninety-two
per cent. of the proteins, ninety-five per cent. of the fats, and
ninety-seven per cent. of the carbohydrates are retained by the body.
_In digestion, it is of the utmost importance that the muscular,
mucous, and submucous coats, and the secreting glands of the stomach
and intestines be kept thoroughly strong and active, that the digestive
juices may be freely poured out, the nutriment be freely absorbed,
and the food be moved along the digestive tract. The strength of any
organ is gained through the nutriment in the blood; therefore, daily
exercise, which calls the blood freely to these organs is imperative.
Daily exercise should be directed to the vital organs. A walk for
exercise is not sufficient._
* * * * *
[Sidenote: Absorption of Food]
The greater part of the food is absorbed through the intestines, yet
some proteins which have been fully digested by the gastric juice, and
certain fats, particularly the fats in milk, which are in a natural
state of emulsion, may be absorbed through the walls of the stomach.
However, the absorption through the stomach is small compared to that
through the small intestine.
[Illustration: DIAGRAMMATIC REPRESENTATION OF VILLUS.
_a_, 1, cylindrical or “sucking” cells; 2, goblet cell; 3, capillaries;
4, food particles ready for absorption by the cells; _b_, cylindrical
and goblet cells seen from above.—Adapted from LANDOIS.]
The small intestine is peculiarly fitted for absorption. Its mucous
lining is thrown up into folds to furnish a larger surface for this
purpose. The folds hold the food as it passes toward the large
intestine, until the villi have the opportunity to absorb it.
These transverse folds of the intestinal walls are called _valvulæ
conniventes_.
The villi are tiny finger-like projections of the mucous lining of the
intestines, which stand out of the lining somewhat as the nap on plush.
They have been called “sucking” villi, because during the movements of
the intestines they seem to suck in the liquid food.
As soon as the foodstuffs—proteins, carbohydrates, and fats—are put in
an absorbable state called chyle, they are very promptly taken up by
the villi.
If for any reason the chyle remains unabsorbed, it is liable to be
attacked by the bacteria always present in the intestines, and gases
form.
The peptones, sugars, and saponified fats are rapidly absorbed, while
the undigested portion, together with the unabsorbed water, the bile,
mucus, and bacterial products, are passed through the ileocecal valve
into the large intestine.
The mass passes up the ascending colon, on the right side of the
abdomen, across the transverse, and down the descending colon, on
the left side, losing, by absorption, the small amount of foodstuffs
not absorbed in the stomach and small intestine. That the large
intestine is to some extent adapted to absorption is shown by clinical
experiments with patients who cannot retain food in the stomach, the
food in such cases being given through rectal injections.
While water and salt are absorbed in both the stomach and small
intestine, the larger part of the water passes into the large
intestine, that it may assist the passage of the intestinal contents.
Water also stimulates peristaltic movements.
As the food is absorbed through the walls of the alimentary canal, it
is picked up by the rootlets of the mesenteric veins and by the lymph
channels—the latter through the abdominal cavity are called lacteals.
Nearly all of the fats are absorbed through the lacteals. The whitish
color given to the contents of the lacteals, by the saponified fats,
gives rise to the term “lacteal.”
Nearly all of the proteins and sugars pass through the mesenteric veins
and the portal veins to the liver. Here the sugars are at once attacked
by the liver cells and built up into glycogen as described on pages 151
and 159. A small portion of the proteins, however, do not go to the
liver, but are passed directly into the lymphatics and thus into the
blood stream, where they are again carried to the liver, and the urea
is separated.
* * * * *
To sum up, the larger part of the sugars, starches, proteins, and fats
is absorbed through the small intestine, a small amount being absorbed
in the stomach and a very little through the large intestine. While
some water and salts are absorbed in the stomach and small intestine,
these are largely absorbed in the large intestine.
* * * * *
[Sidenote: Economy in Food]
It is economy to keep the digestive organs and the circulation and
tissues strong, in order that all foods eaten may yield returns,
instead of hampering the activity of the body.
The food which furnishes the most tissue-building substance and yields
the most heat and energy, with the least refuse, is the economical
food, provided it is varied enough to meet the psychical needs as well
as the physical.
Whether or not a food is economical depends on the degree to which it
stimulates the activity of the mind as well as the body. Preparation
and serving here are as important as the material to be served.
Economy in food is a question into which many factors should enter.
A cheap food is not always an economical food. Amount and keeping
qualities, palatability, ripeness or unripeness, the age, habit, and
occupation of the partakers, all have their share in the problem.
In the selection of food for any individual, the result to be gained
from the food must be borne in mind. If one is doing heavy muscular
work, more protein to rebuild tissue, as well as more carbohydrates and
fats to produce energy, are required than if one’s habits of work are
sedentary.
In mental work, in which the brain is continually active, proteins are
required to resupply the brain tissue, but the fats and carbohydrates
may be lessened. If the brain is sufficiently active to use all of the
fuel in brain energy one does not accumulate fat.
In sedentary occupations, which do not call for hard and continuous
mental activity, the carbohydrates and fats, if taken in excess, are
stored within the system, clogging it and producing torpid liver,
constipation, and obesity.
In a study of tables of food values, in making up a dietary, the
question should be to provide the largest quantity of nutriment at the
lowest cost, with due attention to palatability and variety.
In the selection of meats, for instance, while beef steak may cost
twice as much as beef stew, it must be borne in mind that beefsteak
contains very little waste, and that it contains a large proportion of
albuminoids, or the tissue-building proteins, while, in beef stew, bone
and connective tissue predominate. A large proportion of the proteins
obtained from the beef stew are gelatinoids and extractives—not the
tissue-building albuminoids. (See page 56.)
In comparing the cheaper and the more expensive cuts in the same kind
of beefsteak, however, the cheaper cuts often yield quite as much
nutriment as the more expensive ones. Round steak is just as nourishing
as porterhouse and cheaper, if one considers the greater number of
helpings derived from a pound of round steak than from a pound of
porterhouse.
For the aged or the invalid, however, the question of preparation will
determine the relative economy.
FOOTNOTES:
[5] For a knowledge of the structure and function of the mucous lining
of the stomach and intestines, and of the tributary glands, such as
the liver and pancreas, which is important to a thorough understanding
of digestion, the reader is referred to _Let’s Be Healthy_, of this
series. In this will be found a study of the secretion of digestive
juices, the conditions favoring normal secretions, etc.
[6] Hereafter, in speaking of sugar, after it has been absorbed into
the blood, the reader will bear in mind that the term refers not only
to digested sugar, consumed as such, but also to digested starches
(maltose).
[7] See _Let’s Be Healthy_, by Susanna Cocroft.