What are some common foods with chemical compounds?
Now, it is perfectly true that four elements go a great way
towards building up the world; but, setting aside the question of
brewing punch, they are called carbon, hydrogen, oxygen, and
nitrogen. So universal is their presence in the living and growing
parts of animals and plants, that they are always spoken of as
"organic elements," and science has ascertained exactly the
proportion in which each should exist in a healthy condition of the
human body. That body is incessantly, but imperceptibly, undergoing
a process which cannot be better described than by the expression
of perennial moulting, only that, whereas certain animals cast off
certain parts of their body - their skin, their hair, or their
feathers - every year, we lose a portion of our weight every day ;
that is to say, we should lose it if we did not absorb through our
lungs, the pores of our skin, and our stomachs, sufficient oxygen,
carbon, hydrogen, and nitrogen, to supply the loss caused by the
wear and tear of our daily life. There has even been an attempt
made to prove that our vital organs are entirely renewed every
forty days or so, but for this calculation there can be no really
satisfactory data, although there certainly is constant loss and
gain going on within us. The material for repairing this incessant
waste which is the inevitable result of the activity of our nervous
and muscular system, is not supplied alone by the starch, sugar,
water, and fat, nor yet by the milk, meat and vegetables we
consume, but by a due combination of food material which shall
ensure the proper proportions of albumen, fibrine, and caseine
absolutely-required by our changing frames. These are rather hard
words, but their meaning will be quite plain if we take as familiar
examples of the three indispensable ingredients, the white of an
egg, a piece of lean meat, and a bit of cheese Everyone can
understand that, although these things contain the largest
proportion of one particular substance, still there may be many
other substances in which they are present, all together, and it is
just to teach us this, and to explain to us why we should rather
give our attention to procuring one form of food than another, that
a knowledge of the elements of Practical Chemistry is useful. In
reading the accounts of the hardships and sufferings of explorers
and travellers, we are often surprised to learn that first one
member and then another of the expedition dropped down and died
long before the supplies were actually exhausted. This is
particularly noticeable in the account of Burke and Wills' attempt
to explore the great plains of South Australia, where one by one
the travellers died, not so much from sheer lack of some sort of
food to eat, as from the unhappy circumstance of the only
attainable food being utterly deficient in the ingredients without
which the human body cannot be nourished. For instance, there was
abundance of an alkaline plant on which the natives almost live at
certain times of the year, and occasionally even a few fish were
caught.
But these materials taken by themselves were so weak in
life-supporting properties, that they failed to repair sufficiently
the waste caused by severe exercise and exposure to the weather. A
man may be starved to death, and yet scarcely feel hungry; that is
to say, he may be able to put food into his mouth which will allay
the cravings of his appetite, but which may not have the least
power to nourish his body, so that he will die as surely as though
he had nothing to eat.
It will perhaps only be necessary to take bread and beef as
samples of food which contain in themselves every element required
to build up the human frame, to repair the daily waste, and to
preserve all the conditions of perfect health. The generality of
mankind have found out the value of these substances for themselves
without the aid of science ; but it may be as well to learn
something about bread and beef, for the simple reason that as we
cannot always, under all circumstances, make sure of having them as
food, we may be able to select those substances which come nearest
to them in nutritive value, if we understand the component parts
which make them so important.