THE VARIETIES OF FOOD.
NITROGENOUS ANIMAL FOODS.—These are divided into two groups, the
one containing gelatin, and the other all the proteid or albuminoid
substances, which are taken in the flesh of various animals, and in
milk and eggs.
=Gelatin= is obtainable from bones, and from connective tissue wherever
found. Being easily digested, and absorbed, it has been very popular as
an invalid’s food; but the fact that animals cannot sustain life on it
without the addition of proteids proves that its value is limited. It
is incapable of building tissues, but is a valuable _proteid-saver_,
being able to save from metabolism half its weight of proteid, or twice
as much as is spared by an equal weight of carbohydrate. Its utility
in this direction is, however, limited, because of the dilute form in
which it is taken in ordinary foods. It is useful for invalids, partly
because it forms a bulk, and prevents the evil tendency to give their
food in too concentrated a form; partly because it forms a source of
easily metabolised material, and so prevents tissue-waste; and partly
because it commonly contains phosphate of lime, derived from the bones
forming the source of gelatin.
Gelatin as prepared for the table contains a considerable proportion of
water; as little as one per cent. of gelatin in water will cause it to
gelatinise on cooling. Isinglass obtained from the floating bladder of
the sturgeon is an example of the purest kind of gelatin; glue is an
inferior sort, made from bones, etc.
Gelatin is only a cheap food when obtained, for instance, from bones
which cannot otherwise be utilised. When made from veal it is costly
out of proportion to its dietetic value.
The =Flesh= of various animals is one of the main sources of our
nitrogenous and fatty food. Meats may be divided into two kinds, viz.,
=red meat= and =white meat=. These gradually merge into one another. As
common examples of red meats, we have beef, mutton, pork, game, wild
fowl, and salmon.
The common fowl and turkey, most fishes, rabbits, crustaceans, and
molluscs, are examples of white meat. As a rule white meats are more
digestible than red, having more delicate fibres, and containing a
smaller proportion of nitrogenous matter.
Flesh consists almost entirely of muscular tissue, of which there are
two kinds, striped and unstriped.
The striped is the variety most commonly used as food. Unstriped muscle
has a softer texture, but is not so easily masticated as striped,
and for this reason may be indigestible. _Tripe_ is composed of the
unstriped muscle and connective tissue of the stomach of the cow, and
if well cooked forms a cheap and easily digested dish.
_The influence of feeding_ on the quality of the meat is great. In
ill-fed or old animals, connective tissue is more abundant, and the
meat is tougher. Well-fed and fattened meat contains for equal weights
much more nutritious matter than non-fattened meat, the fat which is
deposited in the muscle replacing water and not proteid. Hence the
gain in nutritive value is an absolute one, and is not attained at the
expense of the proteid part of the meat. Young animals, again, contain
more water and fat and a larger proportion of connective tissue than
the full-grown, and are consequently not so nourishing.
Meat ought to be eaten either before the onset of _rigor mortis_, or
near its end, before putrefaction has commenced. During _rigor mortis_
it is denser, tougher, and more difficult to digest than after it.
The proportion of fat in meat varies greatly in different individuals
of the same species, in different animals, and in different parts of
the same animal. According to Dr. Ed. Smith, the proportion of fat in
fat oxen is ⅓, in fat sheep ½, in calves ⅙, lambs ⅓, and fat
pigs ½.
Good meat, whether beef or mutton, ought to have a marbled appearance,
a medium colour, neither pale pink nor deep purple; its texture should
be firm, and not leave the impress of the finger; its odour slight and
pleasant, the juice reddish and acid, the bundles of fibres not coarse,
and free from foreign particles imbedded in them; and lastly, it should
not be taken from an animal killed near the time of parturition, nor in
consequence of any accident or disease.
=Beef= is, as a rule, more lean than mutton or pork; it has a closer
texture, and more nutritive material in a given bulk. It is also
fullest of the red-blood juices, and possesses a richer flavour than
the two others.
Liebig’s beef extract contains little if any albumin or gelatin. It
is a useful stimulant to the gastric secretion, as in soups at the
beginning of a meal, but is not a food. Its chief constituents are the
various extractives of meat, the most important of which are inosinic
acid, kreatin (C₄H₉N₃O₂,H₂O), and inosite, or muscle sugar (C₆H_{12}O₆,
2H₂O). Even in substances like Bovril, containing powdered meat fibre
mixed with Liebig’s extract, the amount of nutritive material is very
small. The white of one egg contains as much nutritive matter as three
teaspoonsful of bovril. None of these substances can be trusted like
eggs or milk to keep a patient alive for several weeks.
=Mutton= is regarded as being more suitable for people of sedentary
occupation than beef. =Lamb= is more watery than mutton, and less
nutritious.
=Veal=, as ordinarily prepared in this country, is difficult of
digestion; its shreddy, juiceless fibres eluding the teeth, and
consequently not undergoing proper mastication.
=Pork= is not so digestible as beef or mutton, partly because of the
large proportion of fat, and partly because its fibres are hard and
difficult to masticate. Its digestibility varies greatly with its age,
breeding, and proportion of fat.
The =Flesh of Birds= contains very little fat, and that found separate
from the meat is rarely nice. Most birds are edible, but fish-eating
birds are apt to be nasty. As a rule, the flavour of the male bird is
richer than that of the female. The chief virtues in poultry are their
tenderness, and the large proportion of phosphates they contain. They
are deficient in fat and in iron. To compensate for the former, one
commonly takes with them melted butter and fat bacon or pork sausages;
to compensate for the latter, the addition of Liebig’s extract to the
gravy is useful. Young, and consequently tender, birds are known by
their large feet and leg-joints. When a bird appears at table with
violet-tinged thighs and a thin neck, if possible avoid being helped to
the leg. Wild fowls are harder and less digestible than tame. In ducks
and geese fat is more abundant, and of a stronger flavour; they are,
consequently, not so digestible as fowls.
=Fish= forms an important article of diet. It is easily cooked, and
usually very digestible; it possesses a larger bulk in proportion
to its nutritive quality, and hence is very valuable for those who
habitually take an excess of meat food, which is commonly the case with
those leading sedentary lives, and in declining years. There appears
to be no foundation for the statement that fish is rich in phosphorus,
and is thus a good brain food. Generally, white-fleshed fish is more
digestible than red-fleshed (such as salmon), the latter usually
containing more fat than the former. When the fat is distributed
throughout the flesh, as in the salmon, fish is more satisfying than
when it is mainly stored up in the liver, as in the cod-fish. According
to Payen, the percentage proportion of fat in soles is only 0.248,
in whiting 0.383, conger eel 5.021, mackerel 5.758, eels 23.861. The
addition of some fatty food, as melted butter, is very advisable to
such meats as poultry, rabbits, soles, whiting, plaice, haddock, cod,
turbot, and other fishes; whereas sprats, eels,. herrings, pilchards,
salmon, etc., are more or less rich in fat.
=A Hen’s Egg= usually weighs a little under two ounces. It consists of
74 per cent. of water and 26 per cent. of solid matter. The white of
the egg is chiefly albumin, the yolk consists of a very digestible oil,
rich in phosphorus and iron, each particle of the oil being enveloped
in a form of albumin called vitellin. The salts are chiefly contained
in the shell. There is no sugar in the egg, the necessity for such
oxidisable material for the chick being obviated by the heat produced
by incubation. Eggs, when kept for some time, lose weight, owing to
evaporation through the porous shell; similarly, air entering from
without sets up decomposition. In a solution of brine containing an
ounce of common salt to half a pint of water, fresh eggs sink, stale
ones float; rotten eggs may even float in fresh water. Eggs may be
preserved by keeping them in brine, or, better still in lime water, or
by smearing them over with lard or butter, as soon as possible after
they are laid.
=Cow’s Milk= has a specific gravity of 1028-34, and on allowing it
to stand in a long narrow vessel ought to form ten or twelve per
cent. of its volume of cream. The percentage composition of human
and cow’s milk has been given on page 5. The legal minimum standard
for dairy milk, which is presumably derived from a number of cows,
is now 3 per cent. of fat, and 8.5 per cent. of “solids not fat.”
This standard is unfortunately very low, and allows a considerable
margin of adulteration, which cannot be prevented by legal means. Thus
ordinary milk derived from a herd of cows would probably contain 4.5
per cent. of fat; and it is, therefore, practicable to mix pure new
milk with a large proportion of separated milk, and yet keep within
the legal standard. This is largely done in towns, and infants suffer
much from the deficiency of cream in their sole food (see page 28). The
lactometer determines the specific gravity, which should be taken at
a temperature of 60° F. In skimmed or separated milk it will be over
1034; watering on the contrary lowers the specific gravity. If the milk
has been both watered and skimmed the specific gravity will give an
uncertain indication. Measurement of the cream in a tall narrow glass
will enable one to detect the second possible source of fallacy; but
the composition of milk can only be certainly determined by analysis.
This is done (_a_) by evaporating a weighed amount of milk to dryness
and then re-weighing. (_b_) From a separate amount of dried milk the
fat is extracted by ether, the ether then evaporated, the remaining fat
weighed, and its percentage calculated. The weight of fat deducted from
the total solids i.e. (_b_) from (_a_), gives the “solids not fat.” The
following example will make the method then followed clear. The sample
gives 7.9 per cent. of “solids not fat.” Genuine milk contains at least
8.5 per cent. of “solids not fat.”
Then the sample contains—
100 × 7.9∕8.5 = 92.9 per cent. of genuine milk,
_i.e._ 7.1 per cent. of water has been added to it.
Half a pint of milk supplies as much nitrogenous nutriment as two
good-sized eggs, and as three and a half ounces of beef. Milk may be
deteriorated (1) by skimming or “separating” by machinery, or (2) by
the addition of water—the first diminishing the proportion of fats, and
the second the total amount of solids.
=Skim Milk= still contains nearly 1 per cent. of fat, but =Separated
Milk=, in which the cream has been removed by centrifugal apparatus,
contains less than 1∕8 per cent.
Skim or separated milk forms a cheap source of nitrogenous food; but
when it is sold mixed with new or alone as new milk, the public is
defrauded, and infants fed on it are robbed of the fat which is so
essential for their growth.
=Condensed Milk= is milk deprived of a large part of its water. It
represents three times its volume of fresh milk. There are in the
market (=a=) unsweetened and condensed whole milk, (=b=) sweetened
and condensed whole milk, and (=c=) sweetened and condensed skim or
separated milk. Unfortunately the latter is most largely sold because
cheapest; and infants are thus often robbed of fat, a most important
element in their food. Always examine the label of each tin carefully,
to ascertain whether the milk has been deprived of its cream. The law
requires that this fact should be stated on the label. Tins which have
bulged should be rejected. Condensed milk is more easily digested
by infants than new cow’s milk, but it lacks the anti-scorbutic
properties of new milk (see page 28). Even the condensed whole milk
if diluted beyond 1 part of milk to 3 of water is deficient in fat.
Sweetened condensed milk has one-third its weight of extraneous sugar
added to it, and on this account it tends in children to produce
fatness, and a distaste for simple food; in children fed on it alone
ossification (formation of bone) is retarded, and resistance to illness
is diminished. The only dietetic advantages it possesses over fresh
cow’s milk are its freedom from possible disease germs and easier
digestibility.
The =digestion of milk= is preceded by its clotting in the stomach.
The same thing happens when =junket= is formed by the addition of
rennet to milk. This is a different process from the curdling of
milk, which occurs when milk turns sour. The latter is caused by the
splitting up of milk sugar and the formation of lactic acid by certain
micro-organisms in the milk. When milk is heated, a skin is formed,
consisting of coagulated albumin, in which is also a little casein,
fat, and salts of lime. Boiled milk becomes sterilized. Cow’s milk
should always be boiled, unless it is quite certain that the cows from
which it is derived are perfectly healthy, and that the milk has not
been exposed to infection before reaching the house. The =disadvantages
of boiling= which are outweighed by its advantages, are that the taste
of the milk is altered, some nutritive matter is lost by the formation
of the “skin,” and the casein is not quite so easily digested.
=Pasteurization= of milk, _i.e._ keeping it at a temperature of 70°
C. (158° F.) for 20 to 30 minutes has been proposed as an alternative
to boiling. This appears to destroy the bacilli causing tuberculosis
(see page 312). The typhoid bacilli are killed at 60° C. in five
minutes when suspended in emulsion. Pasteurization is not, however, so
certainly efficacious for other disease-germs as is boiling, and is not
so easily carried out in domestic life as boiling. By boiling milk in a
double saucepan, _i.e._ in a water-bath, very little change occurs in
the taste of the milk, especially if it be cooled rapidly and strained.
=Cheese= is prepared by coagulating milk by “rennet,” the mucous
membrane of the fourth stomach of the calf, salted and dried before
using. By this means the casein is precipitated, carrying down with
it the cream, and a large proportion of the salts of milk. The whey,
containing the sugar, soluble albumin, and remaining salts, is
separated by straining, while the mixed curd and fat are pressed in
moulds. Cheese thus consists of casein, fat in varying proportions,
water and salts, especially phosphate of lime. It is coloured with
annatto, a vegetable colouring matter. When new, cheese is tough; when
old, its oils tend to become rancid; the best age is from nine to
twenty months. It is probable that cheese in small amount helps the
digestion of other foods, though it is itself a highly concentrated
and comparatively indigestible food. When toasted it is proverbially
indigestible.
There are many different kinds of cheese. The following classification
gives the more important varieties:—
(1) Cream cheese is the new curd only slightly pressed, and is more
digestible than ordinary cheese.
(2) Next to these are cheeses made with whole milk rich in cream, such
as Stilton, Gorgonzola, Cheshire, and Cheddar.
(3) Cheeses made of poor or partially skimmed milk, such as
Shropshire, Single Gloucester, and Gruyère.
(4) Cheeses made of skimmed milk, such as Suffolk, Parmesan, and Dutch.
American cheeses may belong to any of these classes; they are generally
pure, but occasionally are made from separated milk, margarine being
added to take the place of cream. The sale of such cheeses, except
under the name of “margarine cheese,” is now illegal.
NON-NITROGENOUS ANIMAL FOODS.—These are all fats, and the most
important are the various meat fats and butter. They possess a higher
food value than carbohydrates in the proportion of 2¼ to 1. The
composition of the various fats differs somewhat; they usually contain
varying proportions of olein, palmitin, and stearin, which are
compounds of glycerine with the radicle of a fatty acid (stearin =
C₃H₅ (C_{18}H_{35}O₂)₃). Thus mutton suet consists of stearin, olein,
and palmitin, with a preponderance of stearin. Beef suet contains
less stearin and more olein than mutton suet. The more olein a fat
contains the less solid it is. Olive oil is composed almost entirely of
olein. Palmitin, which melts sooner than stearin, is the chief solid
constituent of butter, while olein is its chief liquid constituent.
Butter is specially distinguished by containing 7 to 8 per cent. of
“volatile fatty acids,” such as butyric, caproic, etc., combined with
glycerine. The presence and amount of these compounds is an important
test for the freedom of butter from adulterating fats.
Cod-liver oil is next to butter the most digestible animal fat known.
The best cod-liver oil is frozen at a low temperature, by which means
the stearin is frozen out, and nearly pure olein is left. Traces of
iodine have been found in it, and more commonly a small amount of bile,
which probably increases its digestibility.
The temperature at which a fat becomes hard is a fair guide to its
digestibility. Thus we know that beef, and still more, mutton fat,
would become solid, under conditions in which bacon dripping is still
soft. Where digestion is weak, there may be an instinctive loathing
of fat meat; for such persons, especially for children, some other
fat should always be substituted. Thus the addition of butter to the
potatoes makes up the deficiency.
=Butter= forms 3½ to 4½ per cent. of cow’s milk. It is separated
from milk by churning, the oil particles being deprived by this means
of their albuminous coats. The more completely the butter-milk is
separated the longer the butter keeps. It can be kept longer if salt is
added, or in hot weather by keeping it under frequently-changed water.
Rancidity indicates the decomposition of traces of the fat of butter
into its fatty acid and glycerine.
Cream contains about 30 per cent. of butter fat, Cheshire cheese 25 per
cent., and skim milk cheese 7 per cent.
Butter milk differs from skim milk in the presence of lactic acid.
It is more digestible than skim milk, the casein being in a more
flocculent condition.
The odour and flavour of butter are not due to olein and palmitin, the
two chief constituents, but to a smaller quantity of butyrin, caproin,
and caprylin fats of a much lower series. Ordinary butter contains
a considerable proportion of water, and the presence of about 8 per
cent. renders it more palatable; if it is over 15 per cent., the butter
is considered adulterated. An excessive amount of salt is sometimes
present. The most frequent adulteration is the substitution of foreign
fats for butter fat, _e.g._ lard, palm oil, rape seed oil, or cocoa-nut
oil. Margarine is most frequently used for this purpose.
=Margarine= is prepared from beef-fat by melting, the stearin
becoming solid again at a temperature at which olein and margarine
still remain liquid. It forms a wholesome and cheap food, being
nearly as digestible as butter, for which more expensive food it
is often fraudulently sold. When mixed with a small proportion of
butter its recognition by smell, etc., is almost impossible, but
on careful chemical analysis, it is found to have a higher melting
point and a lower specific gravity than butter, and a much smaller
percentage of soluble fatty acids than the latter. Thus:—
┌───────────┬──────────┬──────────┬──────────────────────────────────┐
│ │ MELTING │ SPECIFIC │ SAPONIFICATION AND FORMATION │
│ │ POINT. │ GRAVITY. │ OF INSOLUBLE FATTY ACID. │
├───────────┼──────────┼─────────────────────────────────────────────┤
│_Butter_ │ 32° C. │ .913 │ 88 per cent. insoluble fatty acid│
│_Margarine_│ 35° C.[1]│ .904─.907│ 95[2] „ „ „ │
└───────────┴──────────┴──────────┴──────────────────────────────────┘
CEREAL FOODS.—Gluten is peculiar to plants, and is chiefly found in
plants belonging to the great family of grasses. Gluten is to bread
what casein is to milk, and myosin to flesh. If one takes a piece of
dough made from wheat flour, and holds it under a stream of water from
the tap, a large part of it is washed away, while a sticky adherent
mass is left behind. This is gluten, and it is its tenacity which
enables bread to be made. If the fluid with which the dough was washed
is collected, it will be found to contain a large quantity of starch,
a small amount of sugar, of albumin, and certain salts. All cereals
possess these constituents in various proportions, as may be seen from
the following table:—
┌──────────────┬──────┬────────┬────┬──────────────┬──────────┬───────┐
│ │WATER.│PROTEID.│FAT.│CARBOHYDRATES.│CELLULOSE.│MINERAL│
│ │ │ │ │ │ │MATTER.│
│ ├──────┼────────┼────┼──────────────┼──────────┼───────┤
│_Wheatmeal_ │ 12.1 │ 12.9 │1.9 │ 70.3 │ 1.6 │ 1.2 │
│_Fine wheat │ │ │ │ │ │ │
│ flour_ │ 13.0 │ 9.5 │0.8 │ 75.3 │ 0.7 │ 0.7 │
│_Oatmeal_ │ 7.2 │ 14.2 │7.3 │ 65.9 │ 3.5 │ 1.9 │
│_Barley meal_ │ 11.9 │ 10.0 │2.2 │ 71.5 │ 1.8 │ 2.6 │
│_Maize meal_ │ 11.4 │ 8.5 │4.6 │ 72.8 │ 1.4 │ 1.3 │
│_Rice (husk │ │ │ │ │ │ │
│ removed)_ │ 12.0 │ 7.2 │2.0 │ 76.8 │ 1.0 │ 1.0 │
└──────────────┴──────┴────────┴────┴──────────────┴──────────┴───────┘
The proteid varies in character in the different cereals; wheat flour
has the largest proportion of gluten (8 to 12 per cent.) and therefore
makes the best bread.
Good =wheat flour= ought to be white, not gritty or lumpy, not acid
or musty, forming a coherent stringy dough. Examined microscopically,
it should show the absence of any fungi, or acarus farinæ, or of
foreign starches, such as barley, maize, rice, potato, known by the
different shape of their starch granules. (See Fig. 1.) Alum has been
occasionally added to flour, to enable the baker to make a white
and porous bread from damaged wheat flour. It can be detected as
follows:—Pour over the freshly cut surface of a slice of bread some
freshly prepared decoction of logwood chips, and then a solution of
carbonate of ammonia. If alum is present, the bread turns a marked blue
to violet colour; but if the bread is pure, it is only stained pink.
The wheat grain may be used as food in its entirety. Thus boiled in
milk, after having been soaked in water, it forms the chief constituent
of _frumenty_. Usually it is converted into flour by grinding or
milling. A grain of wheat consists of three parts, an outer envelope,
the _bran_, consisting chiefly of indigestible cellulose, and composing
13½ per cent. of the grain; the kernel, or _endosperm_, which
makes up 85 per cent. of the grain; and the _germ_, forming 1½
per cent. of the grain. In the old method of stone grinding, the
bran was removed, and the germ left along with the endosperm. In the
elaborate processes of modern roller milling, the bran is removed as
in the old grinding, because it cannot without the greatest difficulty
be reduced to powder; and the germ is also removed, because the oil
abundantly present in it is apt to become rancid and spoil the flour,
and because the soluble proteids in it are apt to change some of the
flour into dextrin and sugar, which become brown in baking and spoil
the appearance of the bread. The germ is easily removed, because
its toughness causes it to be flattened out in the milling, while
the endosperm becomes powdery. The central part of the endosperm is
the source of ‘patents.’ It is very rich in starch and is used for
making fancy breads and pastry. The outer part of the endosperm is
‘households.’ ‘Households flour’ is subdivided into (_a_) second
patents, or ‘whites’; (_b_) first households; (_c_) second households
or ‘seconds.’ ‘Seconds’ is richest in gluten, ‘whites’ in starch.
Ordinary bread is normally derived from a blend of these three. Some
‘strong’ wheats, _e.g._ Australian, yield a ‘patents’ which is rich
in gluten, and such flour is used for making Vienna bread. ‘Strong’
wheats take up most water in baking, and so yield most loaves per
sack. ‘Seconds’ flour yields a bread which is richer in proteid than
most other kinds; but the dark colour of the loaf makes it unpopular.
Various schemes have been devised to utilise the germ and the bran,
which are ordinarily discarded. In the preparation of _Hovis flour_ the
separated germ is partially cooked by superheated steam. This kills the
ferment contained in the soluble proteids, and thus prevents it from
changing starch into maltose and dextrin. The action thus prevented is
represented by the following formula:—
STARCH. MALTOSE. DEXTRIN.
10 C₁₂H₂₀O₁₀ + 6 H₂0 = 6 C₁₂H₂₂O₁₁ + 4 C₁₂H₂₀O₁₀.
The germ thus treated is ground to a fine meal, of which one part to
three of ordinary flour, forms Hovis flour. Other ‘germ breads’ are
also in the market. In the making of _Frame food_ the bran is boiled
with water under high pressure. The watery extract, containing the
mineral and part of the nitrogenous constituents of the bran, is
evaporated to dryness, and forms the basis of various preparations. It
is doubtful if this food possesses any great value.
=Brown bread= is a somewhat vague expression, meaning either an
admixture of bran or of germ or of both with flour, or bread made
from whole wheat flour. In each of these cases the loaf would be
brown. The bran is rich in fat as well as in phosphates. It acts as a
mechanical irritant, ill borne by delicate stomachs, but very useful
where a tendency to constipation exists. The excess of nitrogenous
matter in brown bread and its richness in fat, do not prove its greater
nutritiveness, as it is present in a condition in which only a portion
is absorbable from the alimentary canal into the circulation.
The harder wheats, such as Sicilian wheat, contain a larger percentage
of gluten; and from them _macaroni_ and _vermicelli_ are obtained,
which are nearly pure gluten. They are very nutritious and useful
foods. _Semolina_ is prepared from wheat, the millstones being left
sufficiently apart to leave the product in a granular condition. In
_malted_ breads, a syrupy infusion of malted barley (malt extract) is
added to the flour. Malt extract contains in addition to malt sugar
(maltose) and dextrins, a ferment (diastase) which, like the saliva,
is able to convert starch into the soluble substances, maltose and
dextrin (see formulæ above). The action of this ferment is stopped by
the temperature of baking. Hence even when the malt extract is allowed
a considerable time for its operation on the dough, only about 10 per
cent. of the starch in the loaf becomes soluble, as compared with 4 per
cent. in an ordinary loaf.
=Oatmeal=, obtained from the common oat, contains very little gluten,
and so cannot be made into vesiculated bread. It contains a large
proportion of other nitrogenous material and of fat. As porridge and
oatmeal cake it forms a very nutritious diet. The husk ought to be
carefully removed from the meal intended for human food, as, although
very nitrogenous, it acts as a mechanical irritant. Groats consists of
oats from which the husk has been entirely removed. The substitution of
rolling for grinding in preparing oats for food and the application of
heat during the rolling process, have made oatmeal more digestible, as
in Quaker, Provost, and Waverley oats.
=Barley= contains very little gluten; on this account, like oatmeal, it
does not admit of being made easily into bread.
=Malt= is barley which has been made to germinate by heat and moisture
and then dried, “diastase” being formed in the process. _Extract of
malt_, containing diastase in an active condition, is useful in cases
of impaired digestion and deficient assimilation of food.
=Rye= is rarely used in this country for making bread. In Germany
it is known as “black bread,” but its colour and acid taste make it
disagreeable, and it is laxative in its action.
=Maize=, or =Indian Corn=, is deficient in gluten, and so not suitable
for making vesiculated bread. Like oatmeal, it is made into cakes,
called in America “Johnny cake.” It contains much fatty matter, and
is largely used for fattening poultry and other animals. Oswego flour
and corn flour are maize flour deprived by a weak solution of soda, of
its proteids and fat; hominy contains all its constituents. Maize is a
cheap and nutritious food. When wheat flour is dear, it is occasionally
adulterated with maize. The adulteration can be detected by the forms
of the starch granules, examined under a low power of the microscope.
=Rice= contains less proteids and fat than any other cereal. Its chief
value as a food depends on the large amount of starch it contains
(table, page 16).
LEGUMINOUS FOODS.—The chief seeds belonging to this group are peas,
beans, and lentils. They contain a smaller proportion of starch, and
a larger proportion of nitrogenous materials than cereals. Thus while
flour contains 9.5 and bread 8 per cent. of proteid, lean meat 15.18
per cent., and cheese about 30 per cent., peas and beans contain 21 to
26 per cent. (green peas only 4 per cent., dried peas 21 per cent.)
of proteid. The nitrogenous material exists chiefly as legumin, which
has been called vegetable casein. Although leguminous seeds contain
more nutritive material in a given weight than cereals, dietetically
they are inferior, owing to the fact that they are less digestible,
often causing flatulence and other dyspeptic symptoms. Cereals, again,
are more palatable than leguminous seeds, and are more prolific,
and consequently cheaper. In the absence of animal food, legumens
form a useful substitute. They are advantageously diluted with oily
substances, or with rice. The farm-labourer’s dish of broad beans and
fat bacon is founded on strict physiological principles. A mixture of
lentil and barley flour is sold under the name of Revalenta Arabica.
Lentil flour costs 2½d., Revalenta 3s. 6d. per lb. Green peas,
French beans, and scarlet runners are much more easily digested than
are dried peas or beans. Lentils contain the largest proportion of
proteid of any of the pulses. They also contain very little sulphur,
and so do not give rise to the same liberation of sulphuretted hydrogen
in the intestine, as other pulses. The ash of the Egyptian lentil is
particularly rich in iron.
AMYLACEOUS FOODS. Amylaceous or starchy substances are contained in
many of the preceding foods; but some other foods consist almost
entirely of starch. The chief of these are sago, tapioca, and arrowroot.
=Sago= is obtained from the pith of the stems of various species of
palm; a single tree may yield several hundred pounds. Alone it is
easy of digestion. Boiled with milk it forms a light, nutritious, and
non-irritating food. Fictitious sagos are frequently sold, made from
potato starch.
=Tapioca and Cassava= are derived from the tubers of more than one
species of the poisonous family, Euphorbiaceæ. The juices are removed,
and the prussic acid removed by heat. Tapioca only differs from cassava
in being a purer form of starch; the latter is more nutritious, and
among the Indians takes the place of bread.
=Arrowroot= is obtained from the tubers of _Maranta Arundinacea_.
=Tous-les-mois= is a form of starch obtained from the tubers of a West
Indian plant, the _Canna edulis_.
[Illustration: Potato. Wheat. Rice. Oats. Barley. Pea. FIG.
1.—DIFFERENT FORMS OF STARCH GRANULES.]
The =detection= of the varieties of =starch= is usually possible owing
to their fairly characteristic appearance under the microscope. Fig.
1 shows the most important starches. It must be noted that in oats,
maize, and rice the contour is completely marked by facets or surfaces,
while there are less complete markings in tapioca and sago. In wheat,
rye, pea, bean, barley, potato, and arrowroot the contour is even,
though there are minor differences of size and shape.
OTHER VEGETABLE FOODS.—=Green Vegetables= contain comparatively little
nutriment, but form valuable additions to other foods. Cellulose, which
forms their main constituent, although indigestible, forms a bulk
in the alimentary canal, which is necessary to ensure peristalsis.
Concentrated nourishment can only be digested in limited quantity, and
is very apt to produce digestive disorder. Cabbage contains 92 per
cent. of water, and 2½ per cent. nitrogenous matter. Carrots contain
6 per cent. and turnips 2 per cent. of nitrogenous matter; parsnips
are intermediate between these. Green vegetables possess valuable
anti-scorbutic properties. They may be made an important vehicle for
giving fatty food, by adding butter, etc.
Rhubarb and sorrel contain oxalates and tartrates of potash and lime,
to which they owe their tartness. Spinach is cooling and laxative,
like rhubarb, but not tart. Sea-kale, artichoke, and asparagus are
all wholesome vegetables. Asparagus is somewhat diuretic, and gives
a peculiar, disagreeable odour to the urine. Salads, such as mustard
and cress, water-cress, endive, and the garden lettuce are very useful
as anti-scorbutics. Some of them possess a peculiar pungency due to a
volatile oil analogous to that contained in horse-radish.
The =Potato= contains 26 solid parts in 100, of which nearly 20
are starch and 2½ nitrogenous matter. It forms one of our
best-appreciated vegetable foods, and as it possesses valuable
anti-scorbutic properties, its universal use is, perhaps, the chief
cause of the present rarity of scurvy. Alone, it possesses too small a
proportion of nitrogenous material to support life, but the addition
of butter milk makes up this deficiency; and these two together form a
sufficient diet to maintain life and health for a long time.
The =Onion=, =Garlic=, =Leek=, and =Shalot=, all members of the lily
family, are chiefly used as condiments. They contain an acid volatile
oil, which gives them a peculiar odour and flavour. By long boiling,
this is dissipated (as in the case of the Spanish onion), and the onion
is then fairly digestible, as well as nutritious.
=Celery= possesses a more delicate flavour and odour than the
preceding, but even the most tender celery is digested with difficulty;
less so, when boiled or stewed, or a constituent of soups.
Only four =Fungi= are, with us, commonly regarded as safe—mushrooms,
champignons, morels, and truffles; but there are many others which are
equally edible. The food value of fungi has been exaggerated. They are
difficult of digestion and contain little nutritive material. Poisonous
fungi usually have an astringent styptic taste and a disagreeable
pungent odour. In any doubtful case it is better to abstain.
=Oily Seeds= contain a considerable amount of fixed oil which renders
them unfit for persons of weak digestion. The almond, walnut,
hazel-nut, and cocoa-nut are common examples. The sweet almond, when
eaten unbleached, occasionally produces nettlerash, and its solid
texture and large proportion of fixed oils render it difficult of
digestion. The _chestnut_ contains less oil, but a large amount of
carbohydrate. It is extensively used as a food in Italy and some other
countries. In the uncooked condition it is very difficult of digestion.
=Fruits= are chiefly used as adjuncts to other foods; but the vegetable
salts and the cellulose and sugar which they contain, make them very
valuable. =Cucurbitaceous= fruits are used as vegetables rather than
as fruits. Vegetable marrow is wholesome and agreeable, but not very
nutritive. Cucumber is most digestible when rapidly grown and freshly
gathered.
=Stone-fruits= or drupes, such as the peach, nectarine, plum, cherry,
are rather luxuries than foods, like many other fruits. Before ripening
they are unfit for food; when ripening is complete, the acids and
astringent matter largely disappear. The _date_ contains chiefly sugar,
and forms an important food in the East.
=Pomaceous Fruits=, as the apple, pear, and quince, are more digestible
when cooked; and, speaking generally, all fruit not perfectly ripe
should be cooked before eating. The presence of vegetable acids in
fruit soon converts the sucrose of cane sugar into dextrose, a less
sweet variety of sugar. It is therefore more economical to sweeten
after than before cooking.
The chief =Berries= are the grape, currant, gooseberry, cranberry, and
elderberry. The grape is the most important, and 1,500 varieties of it
have been described. Its juice contains a large amount of grape sugar
(dextrose), and small quantities of glutinous material, bitartrate of
potash, tartrate of lime, malic acid, etc.
Besides the above fruits, we have strawberries, mulberries, figs,
plantains, melons, etc., which are all refreshing and anti-scorbutic.
The orange family furnishes us with the orange, lemon, citron, lime,
shaddock, and pomelo, of which the orange is by far the most important,
and possesses most valuable refreshing qualities.
=Sugar= exists in two chief forms, viz. sucroses and glucoses.
=Sucroses=, known chemically as disaccharids (Sucrose = C_12H_22O_11;
compare starch = C_12H_20O_10) are exemplified in cane, beet, maple,
malt (maltose), and milk sugar (lactose). Cane sugar has been gradually
displaced by beet sugar. The two are chemically identical, and equally
nutritious. Maltose is given in malt extract as a food, and because of
the digestive action of the ferment also contained in the extract on
starchy food. Thus:—
STARCH. MALTOSE.
C_12H_20O_10 + H_2O = C_12H_22O_11.
Lactose is comparatively free from sweetness, and is hardly capable of
being fermented by yeasts.
Of =Glucoses= the best example is dextrose = C_6H_12O_6, H_2O,
which can be seen crystallised in dried raisins; it only possesses
one-third the sweetening power of sucrose. Starchy food becomes
changed into glucose by the action of saliva and pancreatic juice in
the alimentary canal. Grapes, cherries, gooseberries, figs, and honey
contain lævulose in addition to glucose (glucose = C_6H_12O_6, H_2O,
lævulose = C_6H_12O_6). Lævulose resembles dextrose except in being
uncrystalline, and in its effect on polarised light. Many ripe fruits,
such as pineapples, strawberries, peaches, citrons, contain sucrose and
lævulose, the latter being not quite so sweet as sucrose.
In the alimentary canal sucroses are inverted into dextrose and
lævulose. Thus natural foods containing these sugars are more readily
assimilated than those containing sucrose.
The sweetening power of the varieties of sugar depends on their degree
of solubility in water. Sucrose is soluble in one-third of its weight
of cold, and in rather more of hot water. Dextrose is soluble in its
own weight of water; lævulose is more soluble, and therefore sweeter
than dextrose. Lactose requires five to six parts of cold and two of
hot water, and is therefore not so sweet as the other varieties.