EXPLANATORY LESSONS
PREPARATION OF FOOD
=Digestibility.= There are comparatively few kinds of food that
can be eaten uncooked. Various fruits, milk, oysters, eggs, and
some other things may be eaten raw, but the great mass of food
materials must be prepared by some method of cooking. All the
common vegetables, such as potatoes, turnips, carrots, beets,
and the different grains, such as rice, wheat, corn, oats, etc.,
neither taste good nor are easily digestible until their starch,
cellulose, and other constituents have been changed from their
compact indigestible form by the action of heat. Some one has
spoken of cooking as a sort of artificial digestion, by which
nature is relieved of a certain amount of work which it would be
very difficult, if not impossible, for her to perform.
=Flavors.= The necessity of cooking to develop, or to create, a
palatable taste is important. The flesh of fowl is soft enough to
masticate, but only a person on the verge of starvation could eat
it until heat has changed its taste and made it one of the most
savory and acceptable of meats. Coffee also well illustrates this
point. When coffee is green--that is, unbrowned--it is acrid in
taste, very tough, even horny in consistency, and a decoction made
from it is altogether unpleasant. But when it is subjected to a
certain degree of heat, for a certain time, it loses its toughness,
becomes brittle, changes color, and there is developed in it a most
agreeable flavor. This flavoring property is an actual product
of the heat, which causes chemical changes in an essential oil
contained in the bean. Heat not only develops but creates flavors,
changing the odor and taste as well as the digestibility of food.
=Effects of Cold.= Some foods are better for being cold; for
example, butter, honey, salads, and ice-cream. Sweet dishes as a
rule are improved by a low temperature. The flavor of butter is
very different and very much finer when cold than when warm. It
is absolutely necessary to keep it cool in order to preserve the
flavor.
CHEMICAL AND PHYSICAL CHANGES
=Chemical Changes.= Since many of the changes which cooking
produces in the different food materials are of a chemical nature,
it is well to consider what constitutes a chemical process.
This idea may perhaps be best conveyed by a few experiments and
illustrations, the materials for which may be easily obtained.
=Exp. with Cream of Tartar and Bicarbonate of Soda.= Mix two
teaspoons of cream of tartar with one of bicarbonate of soda,
in a little warm water. A union of the two substances follows
and they neutralize each other; that is, the cream of tartar is
no longer acid, and the soda is no longer alkaline. Owing to
the power of chemical affinities a separation or breaking up of
these compounds takes place, and new substances, _carbonic acid_
and _rochelle salts_, are formed out of their constituents.
The effervescence which is seen is caused by the escape of the
carbonic acid.
=Exp. with Hydrochloric Acid and Soda.= Put a few drops of
chemically pure hydrochloric acid into a little water; then add
soda. A violent effervescence will follow. Continue putting in
soda until this ceases, when the reaction should be neutral.
Test it with litmus-paper. If it turns blue litmus-paper red, it
is acid; if red litmus-paper blue, it is alkaline. Add acid or
soda, whichever is required, until there is no change produced in
either kind of litmus-paper. The results of this experiment are
similar to those in the first one, namely, carbonic acid and a
salt. In this case the salt is _sodium chlorid_ or _common salt_,
which is in solution in the liquid. Evaporate the water, when
salt crystals will be found.[3]
=Oxid of Iron.= A piece of iron when exposed to the weather
becomes covered with a brownish-yellow coating, which does not
look at all like the original metal. If left long enough it will
wholly disappear, being completely changed into the yellowish
substance, which is _oxid of iron_, a compound of oxygen and
iron, commonly called _iron rust_.
=Burning of Coal.= A piece of coal burns in the grate and is
apparently destroyed, leaving no residue except a little ashes.
The carbon and hydrogen of the coal have united with the oxygen
of the air, the result of which is largely the invisible gas,
_carbonic acid_, which escapes through the chimney.
=Formation of Water.= Water is formed by the union of two
invisible gases, hydrogen and oxygen. It bears no resemblance
whatever to either of them. Its symbol is H_{2}O.
All these are examples of chemical changes.
=Definition of Chemical Change.= Chemical changes or processes
may be defined as those close and intimate actions amongst the
particles of matter by which they are dissociated or decomposed, or
by which new compounds are formed, and involving a complete loss of
identity of the original substance.
=Physical Changes.= Mix a teaspoon of sugar with an equal amount
of salt; the sugar is still sugar, and the salt remains salt; and
they may each be separated from the mixture as such.
Water when frozen is changed from a liquid to a solid; its
chemical composition, however, remains unchanged.
Water converted into steam by heat is changed from a liquid to
a gas, but chemically there is no difference between the one and
the other. _Steam_, _water_, and _ice_ are forms of the same
substance, the difference being physical, not chemical, and
caused by a difference in temperature.
Lead melted so that it will run, and the solid lead of a bullet,
are the same thing.
These illustrate physical changes.
=Definition.= When substances are brought together in such a way
that their characteristic qualities remain the same, the change
is called physical. It is less close and intimate than a chemical
change. The transition from one state into another is also
frequently only a physical change, as is seen in the transformation
of water into steam, water into ice, etc.
ELEMENTS
One feature of the work of the chemist is to separate compound
bodies into their simple constituents. These constituents he
also endeavors to dissociate; and if this cannot be done by any
means known to him, then the thing must be regarded as a simple
substance. Such simple bodies are called _elements_.
=Definition.= An element then may be defined as a simple substance,
which cannot by any known process be transformed into anything
else; that is, no matter how it is treated, it still remains
chemically what it was before. Gold, silver, copper, iron,
platinum, carbon, phosphorus, calcium, oxygen, hydrogen, nitrogen,
and chlorin are examples of elements. Once it was believed that
there were but four elements in the world--earth, air, fire, and
water. Then it was learned that these were not elements at all,
but compounds, and the number of elements increased, until now
sixty-eight are admitted to be simple primary substances. Some of
these may in the future be proven to be compounds. Sulphur is at
present in the doubtful list.
=Oxygen.= Oxygen is an element. It is an invisible gas, without
taste or smell. It is the most abundant substance in the world,
and an exceedingly active agent, entering into nearly all chemical
changes and forming compounds with all known elements except
one--fluorin. It is a necessity of life and of combustion.[4] It
constitutes about two thirds of the weight of our bodies and one
fifth of the weight of the air.
=Hydrogen.= Hydrogen is a gas. It is the lightest substance known.
It unites with oxygen to form water, and, as will be seen later,
enters into the composition of the human body.[5]
=Nitrogen.= Nitrogen is also a gas, but, unlike oxygen, is an
inactive element. It supports neither fire nor life. It is not
poisonous, however, for we breathe it constantly in the atmosphere,
where its office is to dilute the too active oxygen. A person
breathing it in a pure state dies simply from lack of oxygen.
=Carbon.= Carbon is a solid and an important and abundant element.
It is known under three forms: diamond, graphite, and charcoal.
The diamond is nearly pure carbon. Graphite (the "black-lead" of
lead-pencils), coal, coke, and charcoal are impure forms of it.
Carbon is combustible; that is, it burns or combines with oxygen.
In this union carbonic acid is formed, and there is an evolution
of heat, and usually, if the union be rapid and intense enough,
of light. It is the valuable element in fuels, and in the body of
man it unites with the oxygen of the air, yielding heat, to keep
the body warm, and energy or muscular strength for work (Prof.
Atwater). The carbonic acid formed in the body is given out by the
lungs and skin.
=Other Elements.= There are many other elements about which it
would be interesting to note something, such as calcium and
phosphorus (found abundantly in the bones), magnesium, sulphur,
sodium, iron, etc. Samples of these may be obtained to show to
pupils, and descriptions given and experiments made, at the
discretion of the teacher. Of the four most abundant elements of
the body and of food,--oxygen, carbon, hydrogen, and nitrogen,--it
is extremely important that some study be made, and if the
apparatus can be procured, that it be of an experimental nature
rather than simply descriptive.[6]
AIR
Air is made up principally of two elements, nitrogen and oxygen. It
also always contains vapor of water and carbonic acid. Its average
composition is as follows:
Nitrogen 78.49%
Oxygen 20.63%
Aqueous Vapor .84%
Carbonic Acid .04%
These are mixed together, not _chemically united_. Oxygen and
nitrogen do unite chemically, but not in the proportions in which
they exist in the air. Nitrous Oxid (N_{2}O), sometimes called
"Laughing Gas," is one of the compounds of nitrogen and oxygen.
FIRE
=Exp. with a Candle.= Take a tallow candle, and by means of a
lighted match raise its temperature sufficiently high to start an
action between the carbon in the candle and the oxygen of the
air; in other words, light the candle. A match is composed of
wood, sulphur, and phosphorus. The latter is a substance which
unites with oxygen very easily; that is, at a _low temperature_.
By friction against any hard object, sufficient heat is aroused
to effect a union between the phosphorus of a match and the
oxygen of the surrounding air; the flame is then conveyed to
the sulphur, or the heat thus generated causes a union between
it (the sulphur) and the oxygen, sulphur burning somewhat less
freely than phosphorus; this gives enough heat to ignite the
wood, and with its combustion we get sufficient heat to light
the candle, or to start a chemical union between the combustible
portion, carbon chiefly, of the candle and the oxygen of the air.
Allow the candle to burn for a time, then put over it a tall
lamp-chimney; notice that the flame grows long and dim. Next
place on the top of the chimney a tin cover, leaving a small
opening, and make an opening into the chimney from below, with
a pin or the blade of a knife placed between it and the table;
note that the candle burns dimly. Then exclude the flow of air by
completely covering the top; in a moment, as soon as the oxygen
inside the chimney is consumed, the candle will go out.
This shows (1) that air--in other words, oxygen--is necessary to
cause the candle to burn; (2) that by regulating the draft or
flow of air the intensity of the combustion may be increased or
diminished; (3) that by completely excluding air the candle is
extinguished. This experiment with the candle illustrates the way
in which coal is consumed in a stove. By opening the drafts and
allowing the inflow of plenty of oxygen, combustion is increased;
by partially closing them it is diminished, and by the complete
exclusion of air burning is stopped.
The products of the burning of coal are carbonic acid and a small
amount of ash. Twelve weights of coal, not counting the ash,
will unite with thirty-two weights of oxygen, giving as a result
forty-four weights of carbonic acid. Accompanying the union there
is an evolution of light and heat. The enormous amount of carbonic
acid given out daily from fires is taken up by plants and used by
them for food. In the course of ages these plants may become coal,
be consumed in combustion, and, passing into the air, thus complete
the cycle of change.
=Fuel and Kindlings.= The common fuels are coal, coke, wood, gas,
coal-oil, and peat. For kindling, newspaper is good because, being
made of straw and wood-pulp, it burns easily, and also because
printers' ink contains turpentine, which is highly inflammable.
COMPOSITION OF THE BODY
Before entering upon the study of foods it is well to consider
the composition of the human body, that some idea of its chemical
nature may be gained. In the United States National Museum at
Washington may be found some interesting information on this
subject. From there much that is contained in the following pages
is taken.
A complete analysis of the human body has never been made, but
different organs have been examined, and chemists have weighed and
analyzed portions of them, and from such data of this nature as
could be obtained, estimates of the probable composition of the
body have been calculated. Thirteen elements united into their
compounds, of which there are more than one hundred, form it.
The following table gives the average composition of a man weighing
148 pounds.
Oxygen 92.4
Carbon 31.3
Hydrogen 14.6
Nitrogen 4.6
Calcium 2.8
Phosphorus 1.4
Potassium .34
Sulphur .24
Chlorin .12
Sodium .12
Magnesium .04
Iron .02
Fluorin .02
PROF. ATWATER.
It will be seen from this that oxygen, carbon, hydrogen, and
nitrogen constitute nearly the whole, the other elements being in
very small proportions.
PRINCIPAL CHEMICAL COMPOUNDS IN THE BODY
The following interesting table, obtained at the National Museum,
gives the principal compounds of the body. Some of the more rare
organic compounds are omitted.
WATER:--A compound of oxygen and hydrogen.
PROTEIN { _ALBUMINOIDS_ { MYOSIN AND SYNTONIN OF MUSCLE
COMPOUNDS, { or { (sometimes called "muscle
{ _Proteids_. { fibrin").
composed { { Albumen of blood and milk. Casein
mainly of { { of milk.
{
{ { Collagen of bone and }
_Carbon_, { { tendons. } which
{ _Gelatinoids._ { Chondrigen of cartilage, } yield
_Oxygen_, { { gristle, } gelatin.
{
_Hydrogen_, { {
{ _Hemoglobin._ { The red coloring matter of blood.
_Nitrogen_. { {
FATS, { { } These make up the
{ { Stearin, } bulk of the fat of
composed { _Neutral { } the body.
mainly of { Fats._ { Palmitin, } They are likewise
{ { } the chief
{ { Olein, etc. } constituents of
_Carbon_, { { } tallow, lard, etc.
{
_Oxygen_, { _Complex { Protagon, } Found chiefly in
{ Fats_, { } the brain, spinal
_Hydrogen_, { containing { Lecithin, } cord, nerves, etc.
{ phosphorus { }
{ and nitrogen. { Cerebrin. }
CARBOHYDRATES, { Glycogen, "animal starch." Occurs in the
composed { liver and other organs.
of { Inosite, "muscle sugar." Occurs in various
_Carbon_, { organs.
_Oxygen_, { Lactose, "milk sugar." Occurs in milk.
_Hydrogen_. { Cholesterin. Occurs in brain, nerves, and other
{ organs.
{ Phosphate of lime, or calcium }
{ phosphate. } Occurs chiefly
{ Carbonate of lime, or calcium } in bones and
{ carbonate. } teeth, though
{ Fluorid of calcium, or calcium } found in
{ fluorid. } other organs.
{ Phosphate of magnesia, or }
{ magnesium phosphate. }
{
MINERAL { PHOSPHATE OF POTASH, OR POTASSIUM }
SALTS. { phosphate. }
{ Sulphate of potash, or potassium } Distributed
{ sulphate. } through the
{ Chlorid of potassium, or } body in the
{ potassium chlorid. } blood, muscle,
{ Phosphate of soda, or sodium } brain,
{ phosphate. } and other
{ Sulphate of soda, or sodium } organs.
{ sulphate. }
{ Chlorid of sodium, or sodium }
{ chlorid. }
Now, since the body is composed of these substances, our food,
including air and water, should contain them all in due proportion,
that the growth, energy, and repair of the body may be healthfully
maintained.
THE FIVE FOOD PRINCIPLES
For convenience of comparison foods may be divided into five
classes: Water, Protein, Fats, Carbohydrates, Mineral Matters.
Some scientists include air in the list, but it has been thought
best in this work to speak of it separately as the greatest
necessity of life, but not in the sense of a direct nutrient.
An average composition of three of the principles is as follows:
{ Carbon 53
PROTEIN { Hydrogen 7
{ Oxygen 24
{ Nitrogen 16
{ Carbon 76.5
FATS { Hydrogen 12
{ Oxygen 11.5
{ Nitrogen --
{ Carbon 44
CARBOHYDRATES { Hydrogen 6
{ Oxygen 50
{ Nitrogen --
It will be seen from the above that the protein compounds contain
nitrogen; the fats and carbohydrates do not.
WATER
We will now consider the first of the food principles--water. Water
is one of the necessities of life. A person could live without air
but a few minutes, without water but a few days. It constitutes by
weight three fifths of the human body, and enters largely into all
organic matter. Water is an aid to the performance of many of the
functions of the body, holding in solution the various nutritious
principles, and also acting as a carrier of waste. It usually
contains foreign matter, but the nearer it is to being pure the
more valuable it becomes as an agent in the body. Ordinary hydrant,
well, or spring water may be made pure by filtering and then
sterilizing it.
=Exp.= Put a little water into a test-tube, and heat it over
the flame of an alcohol-lamp. In a short time tiny bubbles will
appear on the sides of the glass. These are not steam, as may
be proved by testing the temperature of the water; they are
bubbles of atmospheric gases which have been condensed in the
water from the air; they have been proved to be nitrogen, oxygen,
and carbonic acid, but as they do not exist in the water in the
same proportions as in the air, they are not called _air_, but
_atmospheric gases_. Continue the heating, and the bubbles will
continue to form. After a while, very large bubbles will appear
at the bottom of the tube; they increase rapidly and rise toward
the top; some break before reaching it, but as the heat becomes
more intense others succeed in getting to the surface,--there
they break and disappear. If the water now be tested with a
thermometer, it will be found to have reached 212° Fahrenheit or
100° Centigrade, provided the experiment be tried at or near the
level of the sea.
=Steam.= The large bubbles are bubbles of steam, or water expanded
by heat until its particles are so far apart that it ceases to be
a liquid and becomes a gas. True steam is invisible; the moisture
which collects on the sides of the tube and is seen coming out at
the mouth is partially condensed steam, or watery vapor. Watch a
tea-kettle as it boils on a stove; for the space of an inch or two
from the end of the spout there seems to be nothing; that is where
the _true_ steam is; beyond that, clouds of what is commonly called
steam appear; they are watery vapor formed from the true steam by
partial condensation which is produced by its contact with the cool
air.[7]
=Boiling-point of Water.= Water boils at different temperatures,
according to the elevation above the sea-level. In Baltimore it
boils practically at 212° Fahr.; at Munich in Germany at 209½°; at
the city of Mexico in Mexico at 200°; and in the Himalayas, at an
elevation of 18,000 feet above the level of the sea, at 180°. These
differences are caused by the varying pressure of the atmosphere
at these points. In Baltimore practically the whole weight of the
air is to be overcome. In Mexico, 7000 feet above the sea, there
are 7000 feet less of atmosphere to be resisted; consequently, less
heat is required, and boiling takes place at a lower temperature.
By inclosing a vessel of water in a glass bell, and exhausting
the air by means of an air-pump, water may be made to boil at a
temperature of 70° Fahr., showing that much of the force (heat)
that is consumed in causing water to be converted into steam
is required to overcome the pressure of the air. The foregoing
illustrates the point that _boiling water_ is not of invariable
temperature; consequently, that foods which in some places are
cooked in it may in other places be cooked in water that is not
boiling,--in other words, that it is not ebullition which produces
the change in boiling substances, but heat.
=Changes Produced in Water by Boiling.= By boiling water for a
moderate time the greater part of the atmospheric gases is driven
off. The flavor is much changed. We call it "flat"; but by shaking
it in a carafe or other vessel so that the air can mingle with it,
it will reacquire oxygen, nitrogen, and carbonic acid, and its
usual flavor can thus be restored.
Water which flows through soil containing lime is further changed
by boiling.
=Exp. with Lime-water.= Pour a little lime-water into a
test-tube. With a small glass tube blow into it for a few
minutes, when it will become milky; continue the blowing for a
few minutes more, when it will lose its cloudy appearance and
become clear again. The following explains this: in the first
place there was forced into the lime-water, from the lungs, air
containing an excess of carbonic acid; this united with the lime
in solution in the water and formed carbonate of lime. Carbonate
of lime is insoluble in water which contains no carbonic acid, or
very little,[8] but will dissolve in water which is charged with
it, and this is produced by the continued blowing. Now if this
water be freed of its excess of carbonic acid by boiling, the
carbonate of lime will be freed from its soluble state, and will
fall as a precipitate and settle on the sides of the vessel. From
this we learn that water may be freed from carbonate of lime in
solution in it by boiling.
=Organic Matter in Water.= There is another class of impurities in
water of vastly more importance than either the atmospheric gases
or lime. These are the organic substances which it always contains,
especially that which has flowed over land covered with vegetation,
or that which has received the drainage from sewers. The soluble
matter found in such water is excellent food for many kinds of
micro-organisms which often form, by their multiplication, poisons
very destructive to animal life. Or the organisms themselves may be
the direct producers of disease, as for instance the typhoid fever
bacillus, the bacillus of cholera, and probably others which occur
in drinking-water. These organisms are destroyed by heat, so that
the most valuable effect produced in water by boiling it is their
destruction. Such water is, therefore, a much safer drink to use
than that which has not been boiled. Water should always be boiled
if there is the slightest suspicion of dangerous impurities in the
supply.
=Use of Tea and Coffee.= This leads us to the thought that the
extensive use of tea and coffee in the world may be an instinctive
safeguard against these until recently unknown forms of life. The
universal use of cooked water in some form in China is a matter of
history. The country is densely populated, the sewage is carried
off principally by the rivers, so that the danger of contracting
disease through water must be very great, and it is probable that
instinct or knowledge has prompted the Chinaman to use but very
little water for food except that which has been cooked. Whatever
the reason, the custom is a national one. The every-day drink is
weak tea made in a large teapot and kept in a wadded basket to
retain the heat; the whole family use it. The very poor drink plain
hot water or water just tinged with tea.
That tea and coffee furnish us each day with a certain amount of
wholesome liquid in which all organic life has been destroyed,
remains a fact; they may be, in addition, when _properly made_ and
of _proper strength_, of great value on account of their warmth,
good flavor, and invigorating properties. There is no doubt that
it is of the greatest importance that tea and coffee be used of
_proper strength_; for if taken too strong, disorders of the system
may be produced, necessitating their discontinuance, and thus
depriving the individual of a certain amount of warm and wholesome
liquid.
=To Summarize.= The effects produced in water by boiling which have
been spoken of are: (1) the expulsion of the atmospheric gases; (2)
the precipitation of lime when in solution; and (3) the destruction
of micro-organisms. The most important points to remember in
connection with water are, that a certain amount each day is an
absolute necessity of life, and that unless the supply be above
suspicion it should be filtered and then sterilized.
=Filtration and Sterilization of Water.= Filtration as a general
thing is done by public authorities, but sterilization is not,
and should be done when necessary by the nurse. For immediate
use, simply boiling is said on good authority to be sufficient to
destroy all _organisms_ then in the water. _Spores_ of organisms
are, however, not killed by boiling, as they are very resistant
to heat. Fortunately they are not common. As they do not develop
into bacteria for some hours after the water has been boiled, they
may be entirely gotten rid of by allowing them to develop and then
destroying by a second boiling; but for all practical purposes,
and under ordinary circumstances, water is rendered safe for use
by boiling it once.[9] Should the water be very bad, boil it in a
jar plugged with cotton for half an hour three days in succession,
keeping it meanwhile in a temperature of 70° or 80° Fahr., so
that any _spores_ of organisms which may be in it will have an
opportunity to get into such a state of existence that they will be
capable of being killed by the next boiling. The third treatment
is for the purpose of making sure of any that may have escaped the
first and second.
PROTEIN
The second of the food principles, protein, is a complex and
very important constituent of our food. The protein compounds
differ from all others as to chemical composition by the presence
of nitrogen; they contain _carbon_, _oxygen_, _hydrogen_, and
_nitrogen_, while the fats and carbohydrates are composed
principally of _carbon_, _oxygen_, and _hydrogen_, but no nitrogen.
The so-called extractives or flavoring properties of meats are
nitrogenous, and are consequently classed with the protein
compounds.[10]
The body of an average person contains about _eighteen_ per cent.
of protein. The proteins of various kinds furnish nutriment for
blood and muscle, hence the term "muscle-formers," which is
sometimes given them. They also furnish material for tendons and
other nitrogenous tissues. When these are worn out by use, it is
protein which repairs the waste.
Most of the valuable work upon the analysis of food has been done
in Germany. From estimates made by chemists of that country it has
been decided that the amount of protein in a diet should not fall
below _four ounces daily_. This is to represent an allowance for a
man of average weight doing an average amount of work, below which
he cannot go without loss in health, in work, or in both. Although
protein is the most expensive of all food materials, one should
endeavor to use at least four ounces each day. Meat, milk, eggs,
cheese, fish of all kinds, but especially dried cod, wheat, beans,
and oatmeal are all rich in this substance. The protein compounds
are divided into three classes:
ALBUMINOIDS, GELATINOIDS, EXTRACTIVES.
=Albuminoids.= The most perfect type of an albuminoid is the white
of egg. It is a viscous, glairy, thick fluid which occurs also in
the flesh of meat as one of its juices, in fish, in milk, in wheat
as gluten, and in other foods. It is soluble in cold water.
=Exp.= Mix some white of egg in a tumbler with half a cup of cold
water. As soon as the viscousness is broken up it will be found
to be completely dissolved. It is insoluble in alcohol.
=Exp.= Pour upon some white of egg double its bulk of alcohol. It
will coagulate into a somewhat hard opaque mass.
Heat also has the power of coagulating albumen.
=Coagulation of Albumen by Heat.= Put into a test-tube some white
of egg, and place the tube in a dish of warm water. Heat the
water gradually over a gas-flame or an alcohol-lamp. When the
temperature reaches 134° Fahr. it will be seen that little white
threads have begun to appear; continue the heating to 160°, when
the whole mass becomes white and firm. Now remove a part from the
tube and test its consistency; it will be found to be tender,
soft, and jelly-like. Replace the tube in the dish of water
and raise the heat to 200° Fahr.; then take out a little more
and test again; it will now be found hard, close-grained, and
somewhat tough. Continue the heating, when it will be seen that
the tenacity increases with rise of temperature until at 212°
Fahr., the boiling-point of water, it is a firm, compact solid.
When heated to about 350°, white of egg becomes so tenacious that
it is used as a valuable cement for marble.
These experiments illustrate a very important point in the cooking
of albuminous foods. They show that the proper temperature for
albumen is that at which it is thoroughly coagulated, but not
hardened; that is, about 160° Fahr. Most kinds of meat, milk, eggs,
oysters, and fish, when cooked with reference to their albumen
alone, we find are also done in the best possible manner with
reference to their other constituents. For instance, if you cook
an oyster thinking only of its albuminous juice, and endeavor to
raise the temperature throughout all of its substance to, or near,
160° Fahr., and not higher, you will find it most satisfactory
as to flavor, consistency, and digestibility. The same is true
of eggs done in all ways, and of dishes made with eggs, such as
custards, creams, and puddings. With the knowledge that albumen
coagulates at a temperature of 52° below that of boiling water, one
can appreciate the necessity of cooking eggs in water that is not
boiling, and a little experiment like the above will impress it
upon the mind as no amount of mere explanation can possibly do.
The cooking of eggs, whether poached, cooked in the shell, or in
omelets, is of much importance, for albumen when hard, compact, and
tenacious is very difficult of digestion; the gastric juice cannot
easily penetrate it; sometimes it is not digested at all; while
that which is properly done--cooked in such a way that it is tender
and falls apart easily--is one of the most valuable forms of food
for the sick.
Albumen should always be prepared in such manner as to require the
least possible expenditure of force in digestion. Those who are ill
cannot afford to waste energy. Whether they are forced to do so in
the digestion of their food depends very much upon the person who
prepares it.
Advantage is often taken, in cooking, of the fact that albumen
hardens on exposure to certain degrees of heat, to form protecting
layers over pieces of broiling steak, roast meats, etc. If a piece
of meat is placed in cold water to cook, it is evident, since
albumen is soluble in cold water, that some of it will be wasted.
If the same piece is plunged into boiling water the albumen in its
outer layers will be immediately hardened, and form a sheath over
the whole which will keep in the juices and the very important
flavors. When broth or soup is made, we put the meat (cut into
small pieces to expose a large extent of surface) into cold water,
because we wish to draw out as much as possible the soluble matter
and the flavors. If, on the other hand, the meat is to be served
boiled, and broth or soup is not the object, then this order should
be reversed, and every effort made to prevent the escape of any of
the ingredients of the meat into the liquid.
In broiling steak, we sacrifice a thin layer of the outside to
form a protecting covering over the whole by plunging it into the
hottest part of the fire, so that the albumen will become suddenly
hard and firm, and plug up the pores, thus preventing the savory
juices from oozing out. More will be said on this subject in the
recipes for cooking these kinds of foods.
=Gelatinoids.= The second class of protein compounds comprises the
gelatinoids, gelatin being their leading constituent. It is found
in flesh, tendons, cartilage and bone; in fact, it exists in all
the tissues of the body, for the walls of most of the microscopic
cells of which the tissues are composed contain gelatin.
=Exp.= Boil a pound of lean meat freed from tendons, fat, and
bone, in a pint of water for three hours; then set the liquid
away to cool. Jelly resembling calf's-foot jelly will be the
result. The cell-walls of the flesh have been dissolved by the
long-continued action of heat and liquid. This is commonly called
stock or glaze.
=Exp.= Put a piece of clean bone into a dilute solution of
hydrochloric acid. In two or three days the acid will have acted
upon the earthy matters in the bone to remove them, and gelatin
will remain. The average amount in bone is about thirty per cent.
Calves' feet were formerly used for jelly because of the excess
of gelatin which they contain. They were cooked in water for a
long time and the liquid reduced by further boiling; it was then
clarified, flavored, and cooled; the result was a transparent,
trembling jelly. The prepared gelatin of commerce, or _gelatine_,
has now largely displaced this, for it is much more convenient to
use, and less expensive.
=Extractives.= The extractives or flavoring properties of meats and
other substances are usually classed with the protein compounds.
Their chemical nature is not well understood.
FATS
=Fixed and Volatile Oils.= There are two classes of fats, called
_fixed oils_ and _volatile oils_. All kinds of fats good for food
belong to the class of fixed oils. A volatile oil is one which
evaporates away, like alcohol or water, and leaves no residue.
The fixed oils, at least most of them, will not do this; they
do not vaporize even at very high temperatures, but they become
dissociated or decomposed,--that is, their chemical structure is
broken up before their boiling-point is reached. Volatile oils,
on the contrary, are capable of being boiled and transformed into
gases. Some one illustrates this by the changes which take place in
water. When water is heated to 212° Fahr. it is converted into a
gas, which on cooling below 212° returns to the liquid state again
without loss. The essential oil, turpentine, if heated to 320°
Fahr. ceases to be a liquid and becomes a gas, which on cooling
becomes a liquid oil again without loss of weight. Other volatile
oils are oil of cloves, oil of bitter almonds, orange and lemon
oil, oil of cinnamon, bergamot, and patchouli.
The boiling sometimes noticed in a pot of lard is owing to the
presence in it of a little water which is very soon converted into
steam, when the bubbling ceases, and after that the temperature
of the fat rises rapidly, reaching in a short time four or five
hundred degrees Fahrenheit, when a separation of its constituents
takes place, and carbon is revealed as a black mass.
=Composition of Fats.= Fats are _hydrocarbons_--that is, they
are composed chiefly of carbon united with hydrogen and oxygen.
They must not be confounded with the _carbohydrates_, which are
always composed of carbon with the elements of water--that is, the
proportion of hydrogen to oxygen is as two to one,--whereas in the
hydrocarbons this is not the case. These elements enter into the
compositions of fats as various fatty acids and glycerin; the acids
are not sour, as one would suppose from the name, but are so called
because they behave chemically toward bases as sour acids do, that
is, they unite with them. The glycerin of commerce is obtained by
decomposing fats.
=Fat in Milk.= The white color of milk is given to it by minute
globules of fat suspended in it.
=To prove this=: Put a little milk into a bottle with a
ground-glass stopper; pour upon it three times its bulk of ether
and shake gently; let it stand for two or three days, when it
will be found that the ether has dissolved the fat and left a
semi-transparent yellowish white liquid resembling blood serum.
By pipetting or carefully pouring off the ether, and evaporating
it by placing the vessel containing it in a dish of warm water,
clear oil will be obtained. Care must be taken not to put the
ether near a flame or the fire, as it is highly inflammable, and
an explosion might occur. Ether boils at 94.82° Fahr.
The proportion of fat in milk is from 2.8 to 8 per cent. It
varies in milk from different species of cows, and from the same
species at different times, according to age, feeding, and other
circumstances.
=Cream.= When milk is allowed to stand without disturbance for a
time the globules of fat, being lighter than water, rise to the
surface and form cream. Cream is the most wholesome, palatable, and
easily digested form of fat. Butter is obtained by beating milk or
cream in a churn until the little globules of fat break and stick
together in a mass.
=Olive-Oil.= Olive-oil is one of the most easily digested and
palatable of fats. A genuine oil of the first quality is, in this
country unfortunately, expensive, much of that sold under the name
being adulterated with cotton-seed oil, poppy-oil, and essence of
lard.[11]
Cotton-seed oil has no especially bad flavor, but it is unpleasant
and indigestible when used raw as in sardines and salads. The after
taste which it leaves reminds one too forcibly of castor-oil.
Olive-oil of the best quality is almost absolutely without flavor.
It is prepared in several grades: the first pressing from the fruit
is the best, the second is fair, the third inferior, and there
is sometimes a fourth known as refuse oil. For deep fat frying
nothing is so good as olive-oil, but its costliness in this country
excludes it from common use.
The fat of the sheep and ox, after it has been rendered, and
deprived of all membrane and fibers, is called _tallow_. The term
is also applied to the fat of other animals, and to that of some
plants, as bayberry-tallow, piny tallow, and others. The uncooked
fat of any animal is called _suet_, but the name has come to be
applied to the less easily melted kinds, which surround the kidneys
or are in other parts of the loin. The fat which falls in drops
from meat in roasting is called _dripping_.
THE CARBOHYDRATES
=Starch.= Starch is a substance found in wheat, corn, oats, and
in fact in all grains, in potatoes, in the roots and stems of
many plants, and in some fruits. In a pure state it is a white
powder such as is seen in arrowroot and corn-starch. Examined by
a microscope this powder is found to be made up of tiny grains of
different shapes and sizes, some rounded or oval, others irregular.
Those of potato-starch are ovoid, with an outside covering which
appears to be folded or ridged, and looks somewhat like the outside
of an oyster-shell, although its similarity extends no further
than appearance, as the little ridges are true folds, and not
overlapping edges.
=Size of Starch Grains.= Starch grains vary in size according to
the source from which the starch is obtained. Those of ground rice
are very small, being about 1/3000 of an inch in diameter; those of
wheat are 1/1000 of an inch, and those of potato 1/300 of an inch.
Starch is a carbohydrate, being composed of six parts of
carbon, ten of hydrogen, and five of oxygen. Its symbol is
C_{6}H_{10}O_{5}. It is insoluble in water, but when the water is
heated, the grains seem to absorb it; they increase in size, the
ridges or folds disappear, and when the temperature reaches 140°
Fahr. or a little over, they burst, and the contents mingle with
the liquid forming the well-known paste.
=Test for Starch.= Mix a teaspoon of starch with a cup of cold
water and boil them together for a few minutes until a paste is
formed; then set it aside to cool. Meanwhile make a solution of
iodine by putting a few flakes into alcohol, or use that which is
already prepared, and which may be obtained at any pharmacy. Add
a drop of this solution to the paste mixture; it will immediately
color the whole a rich dark blue. This is known as the "iodine
test," and is a very valuable one to the chemist, for by means of
it the slightest trace of starch can be detected.
=Exp. with Arrowroot.= Make a thin paste by boiling a little
arrowroot and water together. When cool test it with a drop of
the iodine solution. The characteristic blue color will be very
strong, showing that arrowroot is rich in starch.
Similar tests may be made with grated potato, wheat-flour,
rice-flour, tapioca, and other starch-containing substances. Also
powdered sugar, cream of tartar, and other substances may be
tested, when it is suspected that they have been adulterated with
starch.
Although starch grains burst and form a paste with water at 140°
Fahr., that is not the temperature at which it should be cooked
for food, and the thickening which then takes place should not be
confounded, as often happens, with the true cooking of starch.
In order to understand the difference between the proper cooking
of starch and the simple bursting of the grains, let us consider
the changes which take place in starch when it is subjected to
different degrees of heat, and also those which are produced in
it during the process of digestion. All starch in food is changed
into dextrine and then into sugar (glucose, C_{6}H_{12}O_{6}) in
the process of digestion. Glucose is a kind of sugar, resembling
cane-sugar, but it is not so sweet.
=Dextrine.= Dextrine is a substance having the same chemical
nature as starch, but differing in many of its properties. It may
be described as a condition which starch assumes just before its
change into glucose.
=Exp. to show Dextrine.= Carefully dry and then heat a little
starch to about 400° Fahr. Keep it at this temperature until it
turns brown, or for ten minutes. Then mix it with water, when it
will dissolve, forming a gummy solution. Starch will not do this.
Test it with iodine; it will not change color. The remarkable
thing about the relation of dextrine to starch is that although
they differ so much in properties they have the same chemical
composition.
The change of starch into dextrine is an important point in
cooking, because starch cannot be assimilated until the conversion
has taken place, either before or after it is eaten. Now it will
be seen that unless this change is either produced or approached
in the cooking of starch-containing foods, they are not prepared
as well as it is possible to prepare them; also, that it is not
possible to cause this change at a low temperature; therefore
140° (the temperature at which the grains burst) should not be
regarded as the cooking temperature of starch. It should be such a
temperature as shall actually convert it into dextrine, or at least
change it to such an extent that it will be more easily converted
into dextrine, and ultimately into sugar, by the digestive fluids.
This should be as near 401° Fahr. as practicable,--not that a
potato, or a loaf of bread, or a pudding will have all the starch
in it changed when it is put into an oven of that temperature.
It would not be possible, on account of the water contained in
each; but that in the outside may be, and the preparation of the
remainder will be better than at a lower temperature.
There are other means of changing starch into dextrine than
by heat, one of the most remarkable of which is _diastase_, a
substance found in sprouting grains, which has the power to
transform the starch stored in the grain by nature into soluble
dextrine, in which form it can be taken up by the young plant for
food. The crude starch could not thus be absorbed. The starch which
we use as food is of no more value to us than it is to the young
plant until it has been changed into dextrine or sugar. Now, if art
outside of the body can accomplish what nature is otherwise forced
to do in the alimentary canal, the body will be saved a certain
amount of force,--a point of great importance, especially in the
case of the sick or invalid, who can ill afford to waste energy.
Starch constitutes half of bread, our "staff of life"; nearly
all of rice, the staff of life in the East; and the greater part
of corn-starch, sago, arrowroot, tapioca, peas, beans, turnips,
carrots, and potatoes.
_Arrowroot_ is the purest form of starch food known. _Rice_ is
richest in starch of all the grains. _Tapioca_ is prepared from
the root of a tropical plant; it is first crushed and the grains
washed out with water, then the whole is heated and stirred,
thus cooking and breaking the starch grains, which on cooling
assume the irregular rough shapes seen in the ordinary tapioca of
commerce. Probably a part of the starch is converted into dextrine,
which accounts for the peculiarly agreeable flavor which tapioca
possesses. Mixed with the grains, as they are taken from the
plant, is a very dangerous poison which, being soluble in water
and volatile, is partially washed away and partially driven out by
the heat,--in fact the heating is done for this purpose. _Sago_ is
principally starch. It is obtained from the pith of the sago-palm.
Imitations of both tapioca and sago are sometimes made from common
starch.
Starch may be converted into grape-sugar by treating it with
acids; that of corn is generally used for the purpose. Much of the
glucose of commerce is made in this way. In the United States it
is estimated that $10,000,000 worth is manufactured every year.
It is used for table syrup, in brewing beer, in the adulteration
of cane-sugar, and in confectionery. Honey is also made from it.
The nutritive value of vegetables is due largely to the starch and
sugar which they contain.
In the economy of the body starch is eminently a heat producer.
Pound for pound it does not give as much heat as fat, but owing
to its great abundance and extensive use it, in the aggregate,
produces more. (Atwater.)
Starch is an abundant and easily digested form of vegetable food,
but it is incapable of sustaining life. It contains none of the
nitrogenous matter needed for the nutrition of the muscles, nerves,
and tissues. Indeed, it is said on good authority that many an
invalid has been slowly starved to death from being fed upon this
material alone.
=Sugar.= There are many kinds of sugar, the most familiar of which
is _cane-sugar_, or _sucrose_ (C_{12}H_{22}O_{11}). It is obtained
from the juices of various plants, for instance, sugar-cane,
beet-root, the sugar-maple, and certain kinds of palms. By far the
greatest amount comes from the sugar-cane. It is made by crushing
the stalks of the plant (which somewhat resembles Indian corn) and
extracting the sweet juice, which is then clarified and evaporated
until, on cooling, crystals appear in a thick liquid; this liquid
is molasses, and the grains or crystals are brown sugar. White
sugar is obtained by melting this brown sugar in water, removing
the impurities, and again evaporating in vacuum-pans, which are
used for the purpose of boiling the liquid at a lower temperature
than it could be boiled in the open air, thus avoiding the danger
of burning, and otherwise preserving certain qualities of the
sugar. _Loaf-sugar_ is made by separating the crystals from the
liquid by draining in molds; and _granulated_ sugar by forcing out
the syrup in a centrifugal machine. The process of making beet-root
sugar is similar. Sugar from maple sap is obtained by simply
evaporating away the excess of water. In the East a considerable
quantity of sugar is made from the juices of certain varieties of
palm, especially the date-palm. Maple-sugar and palm-sugar are
generally not purified.
Sucrose dissolves readily in water. By allowing such a solution
to stand undisturbed for a time until the water has disappeared,
transparent crystals are obtained, known as _rock candy_. Again,
sucrose melted at a temperature of 320° Fahr. forms, on cooling,
a clear mass, called _barley-sugar_. Heated to 420° Fahr.
dissociation of the carbon from the water of crystallization takes
place, the carbon appearing in its characteristic black color. This
dark brown, sweetish-bitter syrup is called _caramel_. On cooling
it forms a solid, which may be dissolved in water, and is used to
color gravies, soups, beer, and so forth.
=Exp. with Sulphuric Acid.= A very pretty experiment to show the
separation of the water from the carbon may be made by treating
a little sugar in sulphuric acid. Put a tablespoon of sugar in
any vessel that will bear heat, a thin glass or stout cup. Pour
over enough concentrated sulphuric acid to thoroughly moisten it,
let it stand for a few minutes, when it will be seen that the
mass has changed color from white to a yellowish brown. The color
increases in intensity until it is perfectly black, when the
whole puffs and swells up, fumes are driven off, and a mass like
a cinder remains. This is charcoal, or nearly pure carbon.
The explanation is as follows: So strong is the affinity of the
acid for the water that it breaks up the chemical combination
between it and the carbon, unites with the water, and leaves the
carbon free. So intense is the chemical change that an enormous
amount of heat is evolved,--so much, in fact, that a considerable
part of the water is vaporized, leaving the more or less solid
charcoal. The light color noticed during the first part of the
union indicates that the chemical dissociation is just beginning,
and that only a small amount of carbon has been set free.
=Glucose.= Glucose or grape-sugar (C_{6}H_{12}O_{6}) is one of
the kinds of sugar found in grapes, peaches, and other fruits. It
is about two and one half times less sweet than cane-sugar. It is
manufactured on a large scale from the starch of corn.
=Lactose.= Lactose or milk-sugar is the sugar found in the milk of
the _Mammalia_. That of commerce comes chiefly from Switzerland,
where it is made by evaporating the whey of cow's milk. For
sweetening drinks for infants and for the sick, milk-sugar is said
to be less liable to produce acid fermentation than cane-sugar, and
also to be more easily digested.
Sugar is a valuable nutrient, being very easily digested and
absorbed. Cane-sugar is converted into glucose in the process of
digestion by the pancreatic juice, and after absorption it is
completely utilized in the body, furnishing heat and probably
energy.
=Effects of Heat on Sugar.= Sugar undergoes various changes,
with different degrees of heat, by loss of some of its water of
crystallization. One of the most remarkable of these is seen in
caramel sauce, which is a rich crimson-brown syrup generally
supposed to contain foreign coloring matter, but which does not.
It is made by melting sugar without water, and heating it until
the desired hue and thickness are reached. Nothing is added, but
something is taken away; that is, some of the water is driven out,
with the result of change in both color and taste.
In a recent article in "The Century Magazine" (November, 1891)
Prof. Atwater touches upon the subject of the production of
artificial foods from the crude materials of the earth, and states,
among other things, that a sugar resembling fruit-sugar has been
made artificially by synthesis, by Prof. Fischer of Würzburg,
Germany.
AIR
Air is a gaseous elastic body which envelops the earth on every
side, extending possibly two hundred miles from its surface, but
all the while growing more and more rare as the distance increases.
When pure it is tasteless and odorless. We really live at the
bottom of an atmospheric ocean, and are pressed upon by its weight.
At the sea-level the pressure upon every square inch of surface is
equal to fifteen pound.
=Atmospheric Pressure Variable.= Atmospheric pressure diminishes
and is constantly variable, according to the height above the
sea-level. If we ascend into the air 5000 feet, it is perfectly
evident that there are 5000 feet less of atmosphere pressing upon
us than at the point from which we started. This diminution of
pressure is often measured by the temperature at which water boils
at different heights.
=Composition.= An average composition of the atmosphere has been
previously stated. Besides nitrogen and oxygen, it always contains
water in the form of vapor, and carbonic acid. The amount of
aqueous vapor in the air changes according to the temperature; the
amount of carbonic acid is also constantly variable. Air usually
contains, in addition to these, traces of ammonia, organic matter
which includes micro-organisms, ozone, salts of sodium, and other
mineral matters in minute and variable quantities.
=Air in Motion.= The atmosphere is almost always in motion. We feel
it in the gentle breeze and the more forcible wind. If it moves
at a slower rate than two and one half feet a second this motion
is not noticeable. Motion in the air is caused by the unequal
heating of portions of it. If from any cause the atmosphere over
a certain region becomes warm, it will expand (all bodies expand
with heat), become lighter, and its tendency will be to move in the
direction of least resistance,--that is, upward; so we say heated
air rises. Currents of cooler air will immediately flow in to take
its place, and thus we have a breeze, a wind, or a gale, according
to the velocity and force with which the currents move. It is upon
a knowledge of these movements that the theory of ventilation is
based. It is because of the constant motion of air-currents that
out of doors, except in densely populated cities, air remains
constantly pure. When poisonous gases and other impurities
accumulate, winds scatter them far and wide until they are so
diluted as to be harmless; or under some conditions they unite
with other things and form new and simple substances of a harmless
nature, while under others, if they are compounds, they may be
decomposed or washed down to the surface of the earth again.
=Impurities.= The chief chemical product of fires and of that
slower combustion breathing is carbonic acid. Plants during the
day, and under the influence of sunlight, take it up from the air
for food, use the carbon for their growth, freeing the oxygen
which man and the lower animals need. Thus is the balance most
beautifully maintained.
Air is purest over the sea and over wind-swept heights of land.
It, however, always contains some foreign substances, and always
micro-organisms except over mid-ocean. Even the upper strata of
atmosphere are not free from microscopic forms of life, as has been
shown in experiments made with hail at the Johns Hopkins Hospital
in 1890 by Dr. Abbott. Large hailstones were washed in distilled
and sterilized water, and then melted, and cultures made from
different layers; in all of these organisms were found, showing
that they extend into the air a long distance from the earth.[12]
Impurities of various kinds are constantly passing into the air,
but so vast is the expanse of the atmosphere as compared with the
impurities daily thrown into it from the lungs of man and the lower
animals, from fires, manufactories, and decomposing matter, that
they quickly disappear.
Air is the greatest or, as one writer says, the most immediate
necessity of life. We could live without it only a few seconds.
We constantly use it, whether sleeping or waking, and perhaps this
accounts in part for the utter carelessness and indifference which
most people have for the quality of that which they breathe. Even
those persons who know something of the nature of air, make but
little effort to provide themselves with a constantly pure supply.
=Effects of Breathing Bad Air.= If the effects of breathing bad air
were immediate, there would then be an immediate remedy for the
present total lack of any systematic means of ventilation in most
houses. But the effects of breathing bad air are, like those of
some slow and insidious poison, not noticeable at once, and often
manifested under the name of some disease which gives no clue to
the true cause.
Dr. Van Rensselaer, in the Orton Prize Essay on Impure Air and
Ventilation, makes the statement that statistics show that of the
causes of mortality the most important and farthest-reaching is
impure air.
=Amount of Air Required for one Person.= Sanitarians have agreed
that each individual requires at least 3000 cubic feet of air every
hour. A room 10 × 15 × 20 holds 3000 cubic feet of air, which
should be changed once every hour in order that one individual
shall have the required amount. If three persons are in the room,
it must be changed three times.
The effect of bad ventilation is well illustrated by the condition
of the horses in the French army some years ago. With small
close stables the mortality was 197 in every 1000 annually. The
simple enlargement of the stables, and consequent increase of
breathing-space, reduced the number in the course of time to 68 in
every 1000, and later, from 1862 to 1866, with some attention paid
to the air-supply, the number fell to 28½ per 1000.[13]
=Necessity for a Constant Supply of Pure Air.= When we consider
that the food we eat and digest cannot nourish the body until it
has been acted upon by oxygen in the lungs, and that this action
must be constant, never ceasing, it will help us to understand the
necessity for a constant supply of air such as shall furnish us
a due proportion of the life-giving principle, oxygen, and which
shall not contain impurities that interfere with its absorption.
We take into the lungs a mixture of nitrogen, oxygen, and carbonic
acid. We give out a mixture which has lost some of its oxygen,
and gained in carbonic acid. Now, unless the amount of oxygen is
what it should be, the blood will not gain from an inspiration the
amount it should receive, consequently it will be but imperfectly
purified and able but imperfectly to nourish the body. So the
whole system suffers, and if a person for a long time continues to
breathe such an atmosphere, the condition of the body will become
so reduced as to produce disease. Even though in other ways one
lives wisely, all the factors of health multiplied together cannot
withstand the one of impure air. We eat food three or four times
daily. Some of us are very particular about its quality. We breathe
air every instant of our lives, but generally we give but little
consideration as to whether it is pure or impure.
=Ventilation.= No attempt will be made here to explain different
devices for ventilation, but only to touch upon the principle
it involves. Its objects are (1) to remove air which has been
breathed once; (2) to remove the products of combustion, whether
from fires, lamps, gas, or other sources; (3) to carry away all
other substances which may be generated from any cause, in a room
or building, as the impurities from manufacturing, those arising
from decaying matter, and micro-organisms. In a climate where
artificial warmth is necessary a part of the year, it is difficult
to warm and ventilate a room at the same time, without causing
unpleasant drafts; but with some knowledge of the necessity of
ventilation, and of the properties of air, one may in some measure
work out a scheme of ventilation adapted to the circumstances in
which he finds himself.
There are always the doors and windows, which may be thrown wide
open at intervals, and in many houses there are fireplaces. If a
window be opened at the bottom at one side of a room, and another
be opened at the top on an opposite side, a current of air will be
established from the first window, passing through the room and out
at the second. This plan will do very well in warm weather when the
temperature outside is about the same as that of the room, but it
would be impracticable in cold weather. Then we may resort to the
very simple plan of placing a board about eight or ten inches wide
across the window at the bottom and inside of the sash. Then when
the lower half of the window is raised, a space is left between
the upper and lower sashes, through which the air passes freely as
it enters, and, being sent into the room in an upward direction,
causes no draft. The board is for the purpose of closing the window
below, and should fit quite close to the sash.
Fireplaces are good, though not perfect, ventilators. Then there
are the preventive measures, such as burning the gas or lamp low
at night, avoiding oil- and gas-stoves, etc.; the latter are the
worst possible means of heating rooms, for not only do they draw
oxygen for burning from the air, but they give out the polluting
carbonic acid and other products of combustion, which in a coal- or
wood-stove go up the chimney.
A well-ventilated room should have an inflow of warm, pure air,
and a means for the removal of the same after it has been used,
the current being so controlled that, although the air is kept in
motion, there is no perceptible draft.
The plan for the heating and ventilation of the Johns Hopkins
Hospital, Baltimore, Maryland, is a most admirable one. Air from
out of doors is conveyed by a flue into a chamber in the wall, in
which are coils of pipe filled with hot water. The air in passing
over these becomes warm, and, rising, passes into the room to
be heated through a register. On the opposite side of the room
is a chimney-like flue, running to the top of the building and
containing two registers, by the opening and closing of which the
movements of the air in the room can be controlled. The temperature
is maintained by the temperature of the water in the pipes, and the
rapidity of the flow.[14]
The ventilation by this method of heating is the most perfect
known to the author, who has lived for two years in a building
thus supplied with warmth and fresh air. The rooms were invariably
comfortable as to temperature, and the air as invariably sweet and
pure.
MILK
Milk is one of our most perfect types of food, containing water
and solids in such proportions as are known to be needful for the
nourishment of the body. A proof of this is seen in the fact that
it is the only food of the young of the _Mammalia_ during the time
of their greatest growth. It contains those food principles in
such amounts as to contribute to the rapid formation of bone and
the various tissues of the body, which takes place in infancy and
childhood; but after this growth is attained, and the individual
requires that which will repair the tissues and furnish warmth and
energy, milk ceases to be a complete food.
=Composition of Cow's Milk.= The composition of cow's milk varies
with the breed and age, care and feeding, of the animals. Cows
which are kept in foul air in stables all the year, and fed upon
bad food such as the refuse from breweries and kitchens, give a
quality of milk which is perhaps more to be dreaded than that
from any other source; for such animals are especially liable to
disease, and are often infected with tuberculosis, pneumonia,
and other fatal maladies. Cows are particularly susceptible to
tuberculosis, and may convey it to human beings either in their
milk or flesh. According to Dr. Miller, cow's milk contains the
following ingredients:
Water 87.4%
Fat 4.0%
Sugar and soluble salts 5.0%
Nitrogenous matter and insoluble salts 3.6%
Another analysis is that of Uffelmann:
Water 87.6%
Albuminoids 4.3%
Fat 3.8%
Sugar 3.7%
Salts .6%[15]
=Characteristics.= Milk from healthy, well-nourished cows should be
of full white color, opaque, and with a slightly yellowish tinge
sometimes described as "cream white." It should vary but slightly
in composition from the above analyses. The fat should not be
less than 2.5%. The amount of fat may be easily determined with a
Feser's lactoscope (Eimer and Amend, New York), directions for the
use of which come with the instruments. It will generally vary from
3% to 4% in good milk. Should it fall below 2.5% the milk should be
rejected as too poor for use. Such milk has probably been skimmed,
or comes from unhealthy or poorly fed cows.
The specific gravity of milk should be from 1.027 to 1.033. This
may be found with a Quevenne's lactometer. If it falls below 1.027,
one has a right to claim that the milk has been watered or that the
cows are in poor condition.[16]
The reaction of good milk varies from slightly alkaline to slightly
acid or neutral. That from the same cow will be different on
different days, even under the same apparent conditions of care,
varying from one to the other, probably because of some difference
in the nature of the food she has eaten. However, if the reaction
is _decidedly_ alkaline, and red litmus-paper becomes a distinct
blue, the milk is not good, and possibly the animal is diseased.
Should the reaction be decidedly acid, it shows that the milk has
been contaminated, either from the air by long exposure, or from
the vessels which held it, with those micro-organisms which by
their growth produce an acid, a certain amount of which causes
what is known as "souring."
Milk from perfectly healthy and perfectly kept cows is _neutral_,
leaving both red and blue litmus-paper unchanged; but as a general
thing milk is slightly acid, even when transported directly from
the producer to the consumer and handled by fairly clean workmen
in fairly clean vessels. Such milk two or three hours old when
examined microscopically is found to contain millions of organisms.
Milk is one of the best of foods for bacteria, many of the ordinary
forms growing in it with exceeding rapidity under favorable
conditions of temperature. Now it has been found that such milk,
although it may not contain the seeds of any certain disease,
sometimes causes in young children, and the sick, very serious
digestive disturbances, and may thus become indirectly the cause of
fatal maladies.[17]
All milk, unless it is _positively known_ to be given by healthy,
well-nourished animals, and kept in thoroughly cleaned vessels
free from contamination, should be sterilized before using. Often
the organisms found in milk are of disease-giving nature. In
Europe and America many cases of typhoid fever, scarlatina, and
diphtheria have been traced to the milk-supply. In fact milk and
water are two of the most fruitful food sources of disease. It
therefore immediately becomes apparent that, unless these two
liquids are above suspicion, they should be sterilized before
using. Boiling water for half an hour will render it sterile, but
milk would be injured by evaporation and other changes produced
in its constituents by such long exposure to so high a degree of
heat. A better method, and one which should be adopted by all who
understand something of the nature of bacteria, is to expose the
milk for a longer time to a lower temperature than that of boiling.
=To Sterilize Milk for Immediate Use.= (1) Pour the milk into a
granite-ware saucepan or a double boiler, raise the temperature to
190° Fahr., and keep it at that point for one hour. (2) As soon as
done put it immediately into a pitcher, or other vessel, which has
been thoroughly washed, and boiled in a bath of water, and cool
quickly by placing in a pan of cold or iced water. A chemist's
thermometer, for testing the temperature, may be bought at any
pharmacy for a small sum, but if there is not one at hand, heat the
milk until a scum forms over the top, and then keep it as nearly as
possible at that temperature for one hour. Do not let it boil.
=To Sterilize Milk which is not for Immediate Use.= Put the milk
into flasks or bottles with narrow mouths; plug them with a long
stopper of cotton-wool, place the flasks in a wire frame to support
them, in a kettle of cold water, heat gradually to 190° Fahr., and
keep it at that temperature for one hour. Repeat this the second
day, for although all organisms were probably destroyed during the
first process, _spores_ which may have escaped will have developed
into bacteria. These will be killed by the second heating. Repeat
again on the third day to destroy any life that may have escaped
the first two.
Spores or resting-cells are the germinal cells from which new
bacteria develop, and are capable of surviving a much higher
temperature than the bacteria themselves, as well as desiccation
and severe cold.[18] Some writers give a lower temperature than
190° Fahr. as safe for sterilization with one hour's exposure, but
190 may be relied upon. Milk treated by the last or "fractional"
method of sterilization, as it is called, should keep indefinitely,
provided of course the cotton is not disturbed. Cotton-wool or
cotton batting in thick masses acts as a strainer for bacteria, and
although air will enter, organisms will not.
All persons who buy milk, or in any way control milk-supplies,
should consider themselves in duty bound to (1) ascertain by
personal investigation the condition in which the cows are kept.
If there is any suspicion that they are diseased, a veterinary
surgeon should be consulted to decide the case. If they are
healthy and well fed, they cannot fail to give good milk, and
nothing more is to be done except to see that it is transported in
perfectly cleansed and scalded vessels. (2) If it is impossible
to obtain milk directly from the producer, and one is obliged to
buy that from unknown sources, it should be sterilized the moment
it enters the house. There is no other means of being sure that
it will not be a bearer of disease. Not all such milk contains
disease-producing organisms, but it all may contain them, and there
is no safety in its use until all bacteria have been deprived of
life.
DIGESTION
=Definition.= Digestion is the breaking up, changing, and
liquefying of the food in the various chambers of the alimentary
canal designed for that purpose. The mechanical breaking up is done
principally by the teeth in the mouth, the chemical changes and
liquefying by the various digestive fluids.[19]
=Digestive Fluids.= The digestive fluids are true secretions. Each
is formed from the blood by a special gland for the purpose which
never does anything else; they do not exist in the blood as such.
Their flow is intermittent, taking place only when they are needed.
The liver, however, is an exception to all the others. It is both
secretory and excretory, and bile is formed all the time, but is
most abundant during digestion.[20]
=Saliva.= The fluid which is mixed with the food in the mouth
is secreted by a considerable number and variety of glands, the
principal of which are the parotid, submaxillary, and sublingual.
Smaller glands in the roof and sides of the mouth, in the tongue,
and in the mucous membrane of the pharynx contribute to the
production of saliva, the digestive fluid of the mouth. The flow
from the parotid gland is greatest. The flow from all the glands is
greatly increased when food is taken, especially if it be of good
flavor. Sometimes the amount is increased by smell alone, as when a
nice steak is cooking, or a savory soup, and sometimes the saliva
is made copious by thought, as when we remember the taste of dishes
eaten in the past, and we say, "It makes the mouth water just to
think of them."
=Amount of Saliva.= According to Dalton the amount of saliva
secreted every twenty-four hours is 42½ oz. Its reaction is almost
constantly alkaline. It is composed of water, organic matter, and
various mineral salts. Ptyalin is its active principle, and is
called by some authors _animal diastase_, or starch converter.
=Gastric Juice.= Gastric juice is the digestive fluid of the
stomach. It is acid. Its flow is intermittent, occurring only at
times of digestion. Its active principle is pepsin.
It is worthy of notice here that the character of the digestive
fluids when food is taken is different from what it is when the
organs are at rest. For instance, the gastric juice which flows
in abundance under the stimulus of food, is not like the fluid
secreted when the stomach is collapsed and empty.
=Pancreatic Juice.= Pancreatic juice is the digestive juice of the
pancreas, and is poured into the small intestine a short distance
below the pyloric opening. Its reaction is alkaline. Its flow is
entirely suspended during the intervals of digestion.
=Bile.= Bile, the fourth in order of the digestive liquids, is the
secretion of the largest gland of the body--the liver. It is poured
into the small intestine by a duct which empties side by side with
the duct from the pancreas. The flow of bile is constant, but is
greatest during digestion.
=Intestinal Juice.= Intestinal juice has been to physiologists a
difficult subject of study. It is mingled with the salivary and
gastric juices at the times of digestion, when it is most desirable
to notice its action. Nearly all authorities agree that it is
alkaline, and that its function is to complete the digestion of
substances which may reach it in an undigested condition.
=Mucus of Large Intestine.= The mucus secreted by the large
intestine is for lubricating only.
=Digestion in Different Parts of the Alimentary Tract.=
Different substances in food are digested in different portions
of the alimentary canal, and by different means. Let us begin
in the mouth. Taking the classes of foods, starch, one of the
carbohydrates, is the one most affected by the ptyalin, or animal
diastase, of the saliva. So energetic is the action of ptyalin on
starch that 1 part is sufficient to change 1000 parts. Starch is
not acted upon by the gastric juice of the stomach at all; however,
the continued action of the saliva is not probably interrupted in
the stomach. The digestion of starch is completed by the action
of the pancreatic and intestinal juices, and consists in its being
changed into soluble glucose, which is absorbed in solution.
=Sugar.= Cane-sugar, or common sugar (also called _sucrose_),
passes through the mouth, unchanged, to the stomach, where
it is converted into glucose by the slow action of the acid
(hydrochloric) of the gastric juice. Dilute hydrochloric acid has
the same action on sugar outside of the stomach.
The action of pancreatic juice on sugar is very marked; it
immediately changes cane-sugar into glucose. The effect of
intestinal fluid is not well understood, but there is the
general agreement that it does not change cane-sugar, neither is
cane-sugar, as such, absorbed in the intestine. Bile does not
affect it, therefore cane-sugar is digested or converted into
glucose either by the stomach or pancreas, or both. It will now be
seen that ultimately the same substance, glucose, is obtained from
both starch and sugar.
=Protein.= We now come to the consideration of the digestion of
the protein compounds, of which albumen may be taken as a type.
Possibly no action except breaking up and moistening takes place
in the mouth.[21] Its digestion begins in the stomach, where its
structure is broken up and a separation and dissolution of the
little sacs which hold it take place. The same thing is partially
accomplished outside of the stomach when white of egg is slightly
beaten and strained through a cloth. Gastric juice further acts on
the albumen itself, forming it into what is called albumen peptone.
The digestion of raw and carefully cooked albumen has been found
to be carried on very rapidly in the stomach, and the change is
essentially the same in both cases, but in favor of the slightly
coagulated. When the albumen is rendered hard, fine, and close in
consistency by over-cooking, then it is less easy of digestion than
when raw.
=Absorption.= It is probable that the greater portion of the
process of digestion and absorption of albumen takes place in the
stomach.
=Fibrin.= Fibrin is also digested in the stomach, and made into
fibrin peptone.
=Casein.= Liquid casein is immediately coagulated by gastric juice,
both by the action of free acid and organic matter.
=Gelatin.= Gelatin is quickly dissolved by gastric juice, and
afterward no longer has the property of forming jelly on cooling.
Gelatin is more rapidly disposed of than the tissue from which it
is produced.
=Vegetable Protein.= The digestion of the vegetable protein
compounds, such as the gluten of wheat and the protein of the
various grains, such as corn, oatmeal, etc., is undoubtedly carried
on in the stomach, but they must be well softened and prepared
by the action of heat and water, or they will not be digested
anywhere; and often corn, beans, and grains of oatmeal are rejected
entirely unchanged. Partially or imperfectly digested proteins are
affected by intestinal juice. It is probable that the function of
this fluid is to complete digestive changes in food which have
already begun in the stomach.
To summarize: The digestion and absorption of nitrogenous compounds
take place in both the stomach and the intestines.
NUTRITION
One of the important points to bring to the notice of pupils in the
study of cookery is the phenomenon of nutrition. It is astonishing
how vague are the ideas that many people have of why they eat food,
and vaguer still are their notions of the necessity of air, pure
and plenty. Once instruct the mind that it is the air we breathe
and the food we eat which nourish the body, giving material for
its various processes, for nervous and muscular energy, and for
maintaining the constant temperature which the body must always
possess in order to be in a state of health, and there is much more
likelihood that the dignity and importance of proper cooking and
proper food will not be overlooked.
A knowledge that the health and strength of a person depend largely
upon what passes through his mouth, that even the turn of his
thinking is modified by what he eats, should lead all intelligent
women to make food a conscientious subject of study.
In general, by the term "nutrition" is meant the building up and
maintaining of the physical framework of the body with all its
various functions, and ultimately the mental and moral faculties
which are dependent upon it, by means of nutriment or food.
The word is derived from the Latin _nutrire_, to nourish. The word
"nurse" is from the same root, and in its original sense means one
who nourishes, a person who supplies food, tends, or brings up.
Anything which aids in sustaining the body is food; therefore, air
and water, the two most immediate necessities of life, may be, and
often are, so classed.
Nutriment exclusive of air is received into the body by means of
the alimentary canal. The great receiver of air is the lungs, but
it also penetrates the body through the pores of the skin, and at
these points carbonic acid is given off as in the lungs. The body
is often compared to a steam-engine, which takes in raw material in
the form of fuel and converts it into force or power. Food, drink,
and air are the fuel of the body,--the things consumed; heat,
muscular and intellectual energy, and other forms of power are the
products.
Food, during the various digestive processes, becomes reduced to a
liquid, and is then absorbed and conveyed, by different channels
constructed for the purpose, into the blood, which contains, after
being acted upon by the oxygen of the air in the lungs, all those
substances which are required to maintain the various tissues,
secretions, and, in fact, the life of the system.
Some of the ways in which the different kinds of food nourish the
body have been found out by chemists and physiologists from actual
experiments on living animals, such as rabbits, dogs, pigs, sheep,
goats, and horses, and also on man. Often a scientist becomes so
enthusiastic in his search for knowledge about a certain food that
he gives his own body for trial. Much valuable work has been done
in this direction during the last decade by Voit, Pettenkofer,
Moleschott, Ranke, Payen, and in this country by Atwater.
No one can explain all the different intricate changes which a
particle of food undergoes from the moment it enters the mouth
until its final transformation into tissue or some form of
energy; but by comparing the income with the outgo, ideas may be
gained of what goes on in the economy of the body, and of the
proportion of nutrients used, and some of the intricate and complex
chemical changes which the different food principles undergo in
the various processes of digestion, assimilation, and use.[22]
Probably hundreds of changes take place in the body, in its
various nutritive functions, of which nothing is known, or they are
entirely unsuspected, so that if we do our utmost with the present
lights which we possess for guidance to health, we shall still
fall far short of completeness. The subject of food and nutrition,
viewed in the light of bacteriology and chemistry, is one of the
most inviting subjects of study of the day, and is worthy of the
wisest thought of the nation.
The body creates nothing of itself, either of material or of
energy; all must come to it from without. Every atom of carbon,
hydrogen, phosphorus, or other elements, every molecule of protein,
carbohydrate, or other compounds of these elements, is brought
to the body with the food and drink it consumes, and the air it
breathes. Like the steam-engine, it uses the material supplied to
it. Its chemical compounds and energy are the compounds and energy
of the food transformed (Atwater). A proof of this is seen in the
fact that when the supply from without is cut off, the body dies.
The raw material which the body uses is the air and food which it
consumes, the greater portion of which is digested and distributed,
through the medium of the blood, to all parts of the body, to renew
and nourish the various tissues and to supply the material for the
different activities of life.
=Ways in which Food Supplies the Wants of the Body.= Food supplies
the wants of the body in several ways--(1) it is used to form the
tissues of the body--bones, flesh, tendons, skin, and nerves; (2)
it is used to repair the waste of the tissues; (3) it is stored in
the body for future use; (4) it is consumed as fuel to maintain the
constant temperature which the body must always possess to be in a
state of health; (5) it produces muscular and nervous energy.[23]
The amount of energy of the body depends upon two things--the
amount in the food eaten, and the ability of the body to use it, or
free it for use.
With every motion, and every thought and feeling, material is
consumed, hence the more rapid wearing out of persons who do severe
work, and of the nervous--those who are keenly susceptible to every
change in their surroundings, to change of weather, even to the
thoughts and feelings of those about them.
We easily realize that muscular force or energy cannot be
maintained without nutriment in proper quality and amount. An
underfed or starving man has not the strength of a well-fed person.
He cannot lift the same weight, cannot walk as far, cannot work
as hard. We do not as easily comprehend the nervous organism, and
generally have less sympathy with worn-out or ill-nourished nerves
than muscles, but the sensibilities and the intellectual faculties,
of which the nerves and brain are but the instruments, depend
upon the right nutrition of the whole system for their proper and
healthful exercise.
So many factors enter into the make-up of a thought that it cannot
be said that any particular kind of food will ultimately produce a
poem; but of this we may be sure, that the best work, the noblest
thoughts, the most original ideas, will not come from a dyspeptic,
underfed, or in any way ill-nourished individual.
The classification of foods has been usually based upon the
deductions of Prout that milk contains all the necessary nutrients
in the best form and proportions, viz., the nitrogenous matters,
fat, sugar, water, and salts; the latter being combinations of
magnesium, calcium, potassium, sodium, and iron, with chlorin,
phosphoric acid, and, in smaller quantities, sulphuric acid.
These different classes seem to serve different purposes in the
body, and are all necessary for perfect nutrition. Some of them
closely resemble each other in composition, but are quite different
in their physiological properties, and in the ends which they
serve. For instance, starch (C_{6}H_{10}O_{5}) has almost the same
chemical formula as sugar (C_{12}H_{22}O_{11}), and yet the one
cannot replace the other to its entire exclusion.
=The Protein Compounds.= In general it may be said that the
carbohydrates are changed into fats, and are used for the
production of force, and that the fats are stored in the body as
fat and used as fuel. The protein compounds do all that can be done
by the fats and carbohydrates, and in addition something more; that
is, they form the basis of blood, muscle, sinew, skin, and bone.
They are, therefore, the most important of all the food compounds.
The terms "power-givers" and "energy-formers" are sometimes applied
to them, because wherever power and energy are developed they are
present, though not by any means the only substances involved in
the evolution of energy. Probably the fats and carbohydrates give
most of the material for heat and the various other forces of the
body. In case of emergency, where these are deficient, the proteins
are used; but protein alone forms the basis of muscle, tendons,
skin, and other tissues. This the fats and carbohydrates cannot
do (Atwater). The different tissues are known from analysis to
contain this complex nitrogenous compound, protein. Now, since the
body cannot construct this substance out of the simpler chemical
compounds which come to it, it becomes perfectly evident that the
diet must have a due proportion of protein in order to maintain the
strength of the body. We get most of our proteins from the flesh of
animals, and they in turn get it from plants, which construct it
from the crude materials of earth and air.
=The Extractives=, usually classed with the protein compounds,
such as meat extract, beef tea, etc., are not generally regarded
as direct nutrients, but, like tea and coffee, are valuable as
accessory foods, lending savor to other foods and aiding their
digestion by pleasantly exciting the flow of the digestive fluids.
They also act as brain and nerve stimulants, and perhaps also in
some slight degree as nutrients.
The principal proteins or nitrogenous substances are _albumen_ in
various forms, casein both animal and vegetable, _blood fibrin_,
_muscle fibrin_, and _gelatin_. All except the last are very much
alike, and probably can replace one another in nutrition.
Modern chemists agree that nitrogen is a necessary element in the
various chemical and physiological actions which take place in the
body to produce heat, muscular energy, and the other powers. Every
structure in the body in which any form of energy is manifested
is nitrogenous. The nerves, muscles, glands, and the floating
cells[24] in the various liquids are nitrogenous. That nitrogen is
necessary to the different processes of the system, is shown by
the fact that if it be cut off, these processes languish. This may
not occur immediately, for the body always has a store of nitrogen
laid by for emergencies which will be consumed first, but it will
occur as soon as these have been consumed. The energy of the body
is measured by its consumption of oxygen. Motion and heat may be
owing to the oxidation of fat, or of starch, or of nitrogenous
substances; but whatever the source, the direction is given by the
nitrogenous structure--in other words, nitrogen is necessary to all
energy generated in the body.
Protein matter nourishes the organic framework, takes part in the
generation of energy, and may be converted into non-nitrogenous
substances.[25] The necessity of the protein compounds is
emphasized when we realize that about _one half_ of the body is
composed of muscle, _one fifth_ of which is protein, and the
nitrogen in this protein can be furnished only by protein, since
neither fats nor carbohydrates contain it. It is therefore evident
that the protein-containing foods, such as beef, mutton, fish,
eggs, milk, and others, are our most valued nutrients. Our daily
diet must contain a due proportion.
The proteins are all complex chemical compounds, which in nutrition
become reduced to simple forms, and are then built up again into
flesh. The animal foods are in the main the best of the protein
compounds, for they are rich in nitrogenous matter, are easily
digested, and from their composition and adaptability are most
valuable in maintaining the life of the body.
A diet of lean meat alone serves to build up tissue. If nothing
else be taken, the stored-up fat of the body will be consumed, and
the person will become thin.[26] Athletes while in training take
advantage of this fact, and are allowed to eat only such food as
shall furnish the greatest amount of strength and muscular energy
with a minimum of fat. The lean of beef and mutton, with a certain
amount of bread, constitute the foundation of the diet.
=Fats.= Most of the fatty substances of food are liquefied at the
temperature of the body. When eaten in the form of adipose tissue,
as the fat of beef and mutton, the vesicles or cells in which the
fat is held are dissociated or dissolved, the fat is set free, and
mingles with the digesting mass. This is done in the stomach, and
is a preparation for its further change in the intestines.
Fats are not dissolved--that is, in the sense in which meats
and other foods are dissolved--in the process of digestion; the
only change which they undergo is a minute subdivision caused
principally by the action of the pancreatic juice. In this
condition of fine emulsion they are taken up by the lacteals; they
may also be absorbed by the blood-vessels.
It has been found that fat emulsions pass more easily through
membranes which have been moistened with bile, and it is probable
that the function of bile is partly to facilitate the absorption of
fat. That the pancreatic juice is the chief agent in forming fats
into emulsion was discovered in 1848. Bile is, however, essential
to their perfect digestion, and we may therefore say that they
are digested by the united action of the pancreatic juice and the
bile.[27]
Fat forms in the body fatty tissues, and serves for muscular
force and heat; it is also necessary to nourish nerves and other
tissues,--in fact, without it healthy tissues cannot be formed. A
proper amount of fat is also a sort of albumen sparer.
It is probable that the fat which is used in the body either to
be stored away or for energy, is derived from other sources than
directly from the fat eaten. From experiments made by Lawes and
Gilbert on pigs, it is evident that the excess of fat stored in
their bodies must be derived from some other source than the
fat contained in their food, and must be produced partly from
nitrogenous matter and partly from carbohydrates, or, at least,
that the latter play a part in its formation. It would appear
from this that life might be maintained on starch, water, salts,
and meat free from fat; but although the theory seems a good one,
practically it is found in actual experiment[28] that nutrition
is impaired by a lack of fat in the diet. The ill effects were
soon seen, and immediate relief was given when fat was added to
the food. Besides, in the food of all nations starch is constantly
associated with some form of fat; bread with butter; potatoes
with butter, cream, or gravy; macaroni and polenta with oil,
and so forth. A man may live for a time and be healthy with a
diet of albuminoids, fats, salts, and water, but it has not yet
been proved that a similar result will be produced by a diet of
albuminoids, carbohydrates, salts, and water without fat. Fat is
necessary to perfect nutrition. Health cannot be maintained on
albuminoids, salts, and water alone; but, on the other hand, cannot
be maintained without them.
Probably the value of fats, as such, is dependent upon the ease
with which they are digested. The fats eaten are not stored in the
body directly, but the body constructs its fats from those eaten,
and from other substances in food,--according to some authorities
from the carbohydrates and proteids, and according to others from
proteids alone.
Fats are _stored away_ as fat, _furnish heat_, and are _used for
energy_; at least, it is probable that at times they are put to the
latter use. The fats laid by in the body for future use last in
cases of starvation quite a long time, depending, of course, upon
the amount. At such times a fat animal will live longer than a lean
one.
Doubtless in the fat of food the body finds material for its
fats in the most easily convertible form. Of the various fatty
substances taken, some are more easily assimilated than others.
Dr. Fothergill, in "The Town Dweller," says that the reason that
cod-liver oil is given to delicate children and invalids is,
that it is more easily digested than ordinary fats, but it is an
inferior form of fat; the next most easily digested is the fat of
bacon. When a child can take bread crumbled in a little of this
fat, it will not be necessary to give him cod-liver oil. Bacon fat
is the much better fat for building tissues. Then comes cream, a
natural emulsion, and butter. He further says there is one form of
fat not commonly looked at in its proper dietetic value, and that
is "toffee." It is made of butter, sugar, and sometimes a portion
of molasses. A quantity of this, added to the ordinary meals,
will enable a child in winter to keep up the bodily heat. The way
in which butter in the form of toffee goes into the stomach is
particularly agreeable.
=Carbohydrates.= The principal carbohydrates are _starch_,
_dextrine_, _cane-sugar_ or common table sugar, _grape-sugar_, the
principal sugar in fruits, and _milk-sugar_, the natural sugar in
milk. They are substances made up, as before stated, of carbon,
hydrogen, and oxygen, but no nitrogen. They are important food
substances, but are of themselves incapable of sustaining life.
The carbohydrates, both starch and sugar, in the process of
digestion are converted into glucose. This is stored in the
liver in the form of _glycogen_, which the liver has the power
of manufacturing; it then passes into the circulation, and is
distributed to the different parts of the body as it is needed.
(The liver also has the power of forming glycogen out of other
substances than sugar, and it is pretty conclusively proved that
it is from proteids, and not from fats. Carnivorous animals, living
upon flesh alone, are found to have glycogen in their bodies.)
It is impossible to assign any especial office to the different
food principles; that is, it cannot be said that the carbohydrates
perform a certain kind of work in the body and nothing else, or
that the proteids or fats do. The human body is a highly complex
and intricate organism, and its maintenance is carried on by
complex and mysterious processes that cannot be followed, except
imperfectly; consequently, we must regard the uses of foods in
the body as more or less involved in obscurity. It is, however,
generally understood that the proteids, fats, and carbohydrates
each do an individual work of their own better than either of
the others can do it. They are all necessary in due amount to
the nutrition of the body, and doubtless work together as well
as in their separate functions. They are, however, sometimes
interchangeable, as, for instance, in the absence of the
carbohydrates, proteids will do their work. The carbohydrates are
eminently heat and energy formers, and they also act as albumen
sparers.
The body always has a store of material laid by for future use.
If it were not for this a person deprived of food would die
immediately, as is the case when he is deprived of oxygen. (Air
being ever about us, and obtainable without effort or price, there
is no need for the body to lay by an amount of oxygen; consequently
only a very little is stored, and that in the blood.)
The great reserve forces of the body are in the form of fatty
tissues, and glycogen, or the stored-away carbohydrates of the
liver; the latter is given out to the body as it is needed during
the intervals of eating to supply material for the heat and energy
of daily consumption, and in case of starvation. That they are
true reserves is shown by the fact that they disappear during
deprivation of food. The glycogen, or liver-supply, disappears
first; then the fat (Martin). The heat of the body can be
maintained on these substances, and a certain amount of work done,
although no food except water be taken.
The principal function of the liver is to form glycogen to be
stored away. It constantly manufactures it, and as constantly loses
it to the circulation. Glycogen is chemically allied to starch,
having the same formula (C_{6}H_{10}O_{5}), but differing in other
ways. Its quantity is greatest about two hours after a full meal;
then it gradually falls, but increases again when food is again
taken. Its amount also varies with the _kind_ of food eaten: fats
and proteids by themselves give little, but starch and sugars give
much, for it is found in greatest quantity when these form a part
of the diet.
=Inorganic Matter and Vegetable Acids.= Water and other inorganic
matter, as the salts of different kinds, and vegetable acids, as
vinegar and lemon-juice, can scarcely be said to be digested. Water
is absorbed, and salts are generally in solution in liquids and are
absorbed with them.
_Water_ is found in all parts of the body, even in the very solid
portions, as the bones and the enamel of the teeth; it also
constitutes a large proportion of its semisolids and fluids, some
of which are nearly all water, as the perspiration and the tears.
Water usually is found combined with some of the salts, which seem
to act as regulators of the amount which shall be incorporated
into a tissue. Water is a necessary constituent of all tissues,
giving them a proper consistency and elasticity. The power of
resistance of the bones could not be maintained without it. It is
also valuable as a food solvent, assisting in the liquefying of
different substances, which are taken up by the various absorbent
tubes, conveyed into the blood, and so circulated through the body.
Most of the water of the body is taken into it from without, but it
is also formed in the body by the union of hydrogen and oxygen.[29]
_Sodium chlorid_, or common salt, is found in the blood and other
fluids, and in the solids of the body, except the enamel of the
teeth; it occurs in greatest proportion in the fluids. The part
that this salt plays in nutrition is not altogether understood.
"Common salt is intermediate in certain general processes, and
does not participate by its elements in the formation of organs"
(Liebig). Salt is intimately associated with water, which plays an
intermediate part also in nutrition, being a bearer or carrier of
nutritious matters through the body.
Salt seems to regulate the absorption and use of nutrients. It is
found in the greatest quantity in the blood and chyle. It doubtless
facilitates digestion by rendering foods more savory, and thus
causing the digestive juices to flow more freely. Sodium chlorid is
contained in most if not all kinds of food, but not in sufficient
quantity to supply the wants of the body; it therefore becomes a
necessary part of a diet.
_Potassium chlorid_ has similar uses to sodium chlorid, although
not so generally distributed through the body. It is found in
muscle, liver, milk, chyle, blood, mucus, saliva, bile, gastric
juice, and one or two other fluids.
_Calcium phosphate_ is found in all the fluids and solids of the
body, held in solution in them by the presence of CO_{2}; both it
and calcium carbonate enter largely into the structure of the bones.
_Sodium carbonate_, _magnesium phosphate_, and other salts play
important parts in nutrition.
The various salts influence chemical change as well as act in
rendering food soluble. For example, serum albumen, the chief
proteid of the blood, is insoluble in pure water, but dissolves
easily in water which has a little neutral salts in it.[30] Salts
also help to give firmness to the teeth and bones.
To recapitulate, food is eaten, digested, assimilated, and consumed
or transformed in the body by a series of highly intricate and
complex processes. It is for the most part used for the different
powers and activities of the system; there is, however, always
a small portion which is rejected as waste. The first change is
in the mouth, where the food is broken up and moistened and the
digestion of starch begins; these changes continue in the stomach
until the whole is reduced to a more or less liquid mass. As the
contents of the stomach pass little by little into the duodenum,
the mass becomes more fluid by the admixture of bile, pancreatic
juice, and intestinal juice, and, as it passes along, absorption
takes place; the mass grows darker in color and less fluid, until
all good material is taken up and only waste left, which is
rejected from the body.
That portion of the food which is not affected by the single or
united action of the digestive fluids is chiefly of vegetable
origin. Hard seeds, such as corn, and the outer coverings of
grains, such as the husk of oatmeal and those parts which are
composed largely of cellulose, pass through the intestinal canal
without change.
It may be remarked here that since the digestive mechanism is
so perfect a structure, and will try to dissolve anything given
it, and select only that which is good, why should there be the
necessity of giving any special attention to preparing food before
it is eaten? The answer is that the absorptive vessels cannot take
up what is not there, neither can the digestive organs _supply_
what the food lacks; therefore, the food must contain in suitable
proportions all substances needed by the body. Also, food which
contains a large proportion of waste, or is difficult of digestion
from over or under cooking, or is unattractive by insipidity or
unsavoriness, overworks these long-suffering organs (the extra
power or force needed being drawn from the blood), and causes the
whole system to suffer. Mal-nutrition, with the long line of evils
which it entails, is the cause, direct or indirect, of most of the
sickness in the world, for it reduces the powers of the system, and
thus enfeebles its resistance to disease.
=Ideal Diet.= "The ideal diet is that combination of food which,
while imposing the least burden upon the body, supplies it with
exactly sufficient material to meet its wants" (Schuster).
In general the digestibility of foods may be summarized as follows:
1. The protein of ordinary animal foods is very readily and
completely digestible.
2. The protein of vegetable foods is much less easily digested
than that of animal foods.
3. The fat of animal foods may at times fail of digestion.
4. Sugar and starch are easy of digestion.
5. Animal foods have the advantage of vegetable foods in that
they contain more protein, and that their protein is more easily
digested. (Atwater.)
A diet largely of animal food leaves very little undigested matter.
The albuminoids in all cases are completely transformed into
nutriment. Fat enters the blood as a fine emulsion.
=Absorption.= The general rule of absorption is that food is taken
into the circulation through the porous walls of the alimentary
tract as rapidly as it is completely digested. A large portion of
liquid is immediately absorbed by the blood-vessels of the stomach.
=Adaptation of Foods to Particular Needs and Conditions.= The
demands of different individuals for nutrients in the daily food
vary with age, occupation, and other conditions of life, including
especially the peculiar characteristics of people. No two persons
are exactly alike in their expenditure of muscular and nervous
energy, so no two will need the same amount or kind of nutriment to
repair the waste.
A man who digs in a field day after day expends a certain amount
of muscular energy. A lawyer, statesman, or author who works with
his brain instead of his hands uses nervous force, but very little
muscular. Brain and muscle are not nourished exactly by the same
materials; therefore, the demand in the way of nutriment of these
two classes will not be the same.
The lawyer might find a feast in a box of sardines and some
biscuit, while the field laborer would look with contempt upon
such food, and turn from it to fat pork and cabbage. This is no
mere difference in refinement of taste, but a real and instinctive
difference in the demands of the two constitutions. Sardines supply
to the brain-worker the material he needs, and the pork and cabbage
to the laborer the heat and energy he expends.
In health the sense of taste is the best guide to what is demanded
by the system, and may as a general rule be followed; but in
sickness that will not do, as the sense of taste in particular is
disturbed by most forms of disease.
When a patient is very ill only the simplest foods will be used,
and those will be prescribed by the physician; but when a patient
is out of danger, and the necessity for variety comes, then the
nurse, by preparing or suggesting dishes, may do much toward
restoring the person to health and strength.
As a very large percentage of diseases arise from imperfect
nutrition (as large as eighty per cent. being given by some
writers), the sense of taste is usually very much disturbed and
dulled in illness; therefore those kinds of food which are savory,
and at the same time easy of digestion and nutritious, should
be selected. The savory quality is very important. A person in
health may endure badly cooked food and monotony in diet; a person
recovering from an illness cannot but suffer by it.
A nurse will find a pleasant field for the exercise of ingenuity
in selecting and preparing such dishes as shall (1) be suited to
the digestive powers of the patient; (2) shall be savory; (3)
shall be sufficiently varied to supply all those materials which
the depleted and exhausted body needs; and (4) shall be in such
judicious quantity as shall increase nutrition, but never overtax
the digestive powers.
The decision of No. 1 (food suited to the digestive powers) is
the most difficult, and here again the doctor will advise for
particular or peculiar diseases.
There are certain things which from their natural composition are
more easy of digestion than others, such, for instance, as milk,
eggs slightly coagulated and raw, beef tea with the _juices in
solution_, cocoa milk, and cocoa, coffee, jellies, gruels, porridge
from prepared grains (except oatmeal) when _thoroughly_ cooked,
oysters alive, rice, venison, and tripe.
No. 2, the _savory_ quality, depends largely upon preparation, and
is under the control of the nurse. A baked potato done in a _hot_
oven, just to the point, and served immediately, is a delicious
dish; overdone, or done in an oven of low temperature, and served
lukewarm, it is very far from appetizing. A steak, if cut thin,
salted, and broiled slowly, will be hard, dry, and lacking in
flavor, but if it is cut thick, at least an inch and a half, better
two inches, broiled for the first minute over very hot coals,
and then slowly, that the heat may have time to penetrate to the
center, and raise the whole to a temperature sufficiently high to
cook it (about 160° Fahr.) without charring the outside, it will
make a dish both wholesome and savory.
No. 3, the next consideration, is that of _variety_, and here the
resources and judgment of the person in charge must come to the
front. Only general hints can be given. Endeavor to supply some
protein, some fat, some of the carbohydrates, and some mineral
matter in each meal. Bread, grains, or potatoes will give the
necessary starch. Sugar is usually supplied with drinks. Milk,
eggs, meat, fish, and oysters will give protein; cream, butter,
bacon, and the fat of other meats will furnish fat, and fruits
and green salads give acids and mineral salts. For the latter,
grapes, apples, carrots, onions, dandelions, and lettuce are very
valuable. Grapes are composed of water with salts in solution, and
glucose; both are absorbed with very little outlay from the system.
The others are every-day foods, but science has taught that their
instinctive use in the past has been a wise one.
No. 4, the _quantity_ of food to offer to a sick person, will
depend upon the individual. Give enough, but rather give to an
invalid _too little_ than too much, especially in the first days
of using solid food; for after some forms of sickness there is
great hunger, and one may injure himself by overeating at such a
time. Furnish a little of each kind of food, but let that little be
of _good quality_ and _perfectly prepared_, so that every morsel
is eatable. It is discouraging to any one to have set before him
food such that much of it must be rejected uneaten. It is very
encouraging, especially to an invalid, to be able to eat all that
is brought him, and for this end cooking and serving are of great
importance. It is necessary to adjust the _proportions_ of the
different kinds of foods to the needs of the consumer, otherwise
all unnecessary material will be rejected from the body as waste,
or will be accumulated in it to interfere with the workings of the
different organs.
In general it may be said that the needs of no two individuals
can be satisfied with exactly the same diet. In sickness it is
the province of the physician to adjust the food to the condition
of the patient. In convalescence the taste of the individual and
the judgment of the nurse or attendant combined will usually not
fail of good results. If an individual craves a certain dish, and
there is no good reason why he should not have it, by all means
procure it. Let only your judgment act. It may be something that
you personally do not like. That should not influence a decision,
provided, of course, that the food is not unwholesome.
We should bear in mind that a sick person is not in the same
condition as ourselves, and that no matter how absurd his cravings
may seem, they may be but perfectly natural longings for those
substances which his depleted and exhausted system needs in order
to be restored to health.