amount of daily work may vary. What would be ample for a person
performing a moderate amount of work would be insufficient for one
who underwent daily great bodily or mental exertions, and would be
too much for one who was taking holiday. It would appear, from the
researches of Dr. Haughton, that the amount of urea daily formed in
the body of a healthy man of average weight varies from 400 to 630
grains. Of this weight it appears that 300 grains results from the
action of the internal organs. It would seem, therefore, that the
amount of flesh-forming food indicated in the preceding paragraph may
be diminished in the proportion of 47 to 40 in the case of a person
taking the minimum of exercise—that is, avoiding all movements save
those absolutely necessary for comfort or convenience. On the other
hand, that amount must be increased in the proportion of 74 to 63 in
the case of a person (of average weight) working up to his full powers.
It will be seen at once, therefore, that a hardworking man, whether
labourer or thinker, must make good flesh-forming food constitute a
considerable portion of his diet; otherwise he would require to take an
amount of food which would seriously interfere with his comfort and the
due action of his digestive organs. For instance, if he lived on rice
alone, he would require to ingest nearly seven pounds of food daily; if
on potatoes, he would require upwards of twenty-one pounds; whereas one
pound and a third of meat would suffice to supply the same amount of
flesh-forming food.
Men who have to work, quickly find out what they require in the way of
food. The Irishman who, while doing little work, will live contentedly
on potatoes, asks for better flesh-forming food when engaged in heavy
labour. In fact, the employer of the working man, so far from feeling
aggrieved when his men require an improvement in their diet, either as
respects quality or quantity, ought to look on the want as evidence
that they are really working hard in his service, and also that they
have a capacity for continuous work. The man who lives on less than
the average share of flesh-forming food is doing less than an average
amount of work; the man who is unable to eat an average quantity of
flesh-forming food, is _unable_ to do an average amount of work. “‘On
what principle do you discharge your men?’ I once said,” relates Dr.
Lankester, “to a railway contractor. ‘Oh,’ he said, ‘it’s according to
their appetites.’ ‘But,’ I said, ‘how do you judge of that?’ ‘Why,’
he said, ‘I send a clerk round when they are getting their dinners,
and those who can’t eat he marks with a bit of chalk, and we send them
about their business.’”
At a lecture delivered at the Royal Museum of Physics and Natural
History at Florence, by Professor Mantegazza, a few years since, the
Professor dwelt on the insufficient food which Italians are in the
habit of taking, as among the most important causes of the weakness of
the nation. “Italians,” he said, “you should follow as closely as you
can the example of the English in your eating and in your drinking,
in the choice of flesh-meat (in tossing off bumpers of your rich
wines),[43] in the quality of your coffee, your tea, and your tobacco.
I give you this advice, dear countrymen, not only as a medical man, but
also as a patriot. It is quite evident, from the way millions of you
perform the process which you call eating and drinking, that you have
not the most elementary notions of the laws of physiology. You imagine
that you are living. You are barely prolonging existence on maccaroni
and water-melons. You neither know how to eat nor how to drink. You
have no muscular energy; and, therefore, you have no continuous mental
energy. The weakness of the individual, multiplied many millions of
times, results in the collective weakness of the nation. Hence results
insufficient work, and thence insufficient production. Thus the returns
of the tax-collector and the custom-house officer are scanty, and the
national exchequer suffers accordingly.” Nor is all this, strange as it
may sound, the mere gossip of the lecture-room. “The question of good
feeding,” says Dr. Lankester, “is one of national importance. It is
vain to expect either brain or muscles to do efficient work when they
are not provided with the proper material. Neither intellectual nor
physical work can be done without good food.”
We have now considered the two principal forms of food, the
heat-forming—sometimes called the _amylaceous_—constituents, and
the flesh-forming or _nitrogenous_ constituents. But there are other
substances which, although forming a smaller proportion of the daily
food, are yet scarcely less important. Returning to our comparison of
the human system to a steam-engine—we have seen how the heat-forming
and flesh-forming constituents of food correspond to the supply of
fuel and water; but an engine would quickly fall into a useless state
if the wear and tear of the material of which it is constructed were
not attended to and repaired. Now, in the human frame there are
materials which are continually being used up, and which require to be
continually restored, if the system is to continue free from disease.
These materials are the mineral constituents of the system. Amongst
them we must include _water_, which composes a much larger portion of
our bodies than might be supposed. Seven-ninths of our weight consists
simply of water. Every day there is a loss of about one-thirtieth
part of this constituent of our system. The daily repair of this
important waste of material is not effected by imbibing a corresponding
supply of water. A large proportion of the weight of water daily lost
is renewed in the solid food. Many vegetables consist principally
of water. This is notably the case with potatoes. Where the water
supplied to a district is bad, so that little water is consumed by the
inhabitants—at least, without the addition of some other substance—it
becomes important to notice the varying proportion of water present
in different articles of food. As an instance of this, I may call
attention to a remarkable circumstance observed during the failure of
the potato crops in Ireland. Notwithstanding the great losses which
the people sustained at that time, it was noticed that the amount of
tea imported into Ireland exhibited a remarkable increase. This seemed
at first sight a somewhat perplexing phenomenon. The explanation was
recognized in the circumstance that the potato—a watery vegetable, as
we have said—no longer formed the chief portion of the people’s diet.
Thus the deficiency in the supply of water had to be made up by the
use of a larger quantity of fluid food; and as simple water was not
palatable to the people, they drank tea in much larger quantities than
they had been in the habit of taking before the famine.
But we have to consider the other mineral constituents of the system.
If I were to run through the list of all the minerals which exist
within the body, I should weary the patience of the reader, and
perhaps not add very much to the clearness of his ideas respecting the
constitution of the human frame. Let it suffice to state generally
that, according to the calculations of physiologists, a human body
weighing 154 pounds contains about 17½ pounds of mineral matter; and
that the most important mineral compounds existing within the body are
those which contain lime, soda, and potash. Without pretending to any
strictly scientific accuracy in the classification, we may say that
the lime is principally found in the bones, the soda in the blood, the
potash in the muscles; and according as one or other of these important
constituents is wanting in our food, so will the corresponding portions
of the frame be found to suffer.
We have a familiar illustration of the effects of unduly diminishing
the supply of the mineral constituents of the body in the ravages
which scurvy has worked amongst the crews of ships which have remained
for a long period ill-supplied with fresh vegetables. Here it is
chiefly the want of potash in the food which causes the mischief.
An interesting instance of the rapid—almost startling—effects of
food containing potash, in the cure of men stricken by scurvy, is
related by Dana. The crew of a ship which had been several months at
sea, but was now nearing the land, were prostrated by the ravages of
scurvy. Nearly all seemed hopelessly ill. One young lad was apparently
dying, the livid spots which were spreading over his limbs seeming to
betoken his rapidly approaching end. At this moment a ship appeared
in view which had but lately left the land, and was laden with fresh
vegetables. Before long large quantities of the life-bearing food had
been transferred to the decks of the other ship. The instincts of life
taught the poor scurvy-stricken wretches to choose the vegetable which
of all others was best suited to supply the want under which their
frames were wasting. They also were led by the same truthful instincts
to prefer the raw to cooked vegetables. Thus the sick were to be seen
eating raw onions with a greater relish than the gourmand shows for
the most appetising viands. But the poor lad who was the worse of the
sufferers had already lost the power of eating; and it was without
a hope of saving his life that some of his companions squeezed the
juice of onions between his lips, already quivering with the tremor of
approaching death. He swallowed a few drops, and presently asked for
more. Shortly he began to revive, and to the amazement of all those
who had seen the state of prostration to which he had been reduced, he
regained in a few days his usual health and strength.
The elements which we require in order to supply the daily waste of
the mineral constituents of the body are contained in greater or less
quantities in nearly all the articles which man uses for food. But it
may readily happen that, by adopting an ill-regulated diet, a man may
not take a sufficient quantity of these important elements. It must
also be noticed that articles of food, both animal and vegetable, may
be deprived of a large proportion of their mineral elements by boiling;
and if, as often happens, the water in which the food has been boiled
is thrown away, injurious effects can scarcely fail to result from
the free use of food which has lost so important a portion of its
constituent elements. Accordingly, when persons partake much of boiled
meat, they should either consume the broth with the meat, or use it
as soup on the alternate days. Vegetables steamed in small quantities
of water (this water being taken with them), also afford a valuable
addition to boiled meat. In fact, experience seems to have suggested
the advantage of mixing carrots, parsnips, turnips, and greens with
boiled meat; but unfortunately the addition is not always made in
a proper manner. If the vegetables are boiled separately in large
quantities of water, and served up after this water has been thrown
away, more harm than good is done by the addition; since the appetite
is satisfied with comparatively useless food, instead of being left
free to choose, as it might otherwise do, such forms of food as would
best supply the requirements of the system. Salads and uncooked fruits,
for instance, contain saline ingredients in large proportion, and
could be used advantageously after a meal of boiled meat. Potatoes are
likewise a valuable article of food on account of the mineral elements
contained in them. And there can be no doubt that the value of potatoes
as an article of food is largely increased when they are cooked in
their skins, after the Irish fashion.
Lastly, we must consider those articles of food which promote the
natural vital changes, but do not themselves come to form part of the
frame, or, at least, not in any large proportion of their bulk. Such
are tea, coffee, and cocoa: alchoholic drinks; narcotics; and lastly,
spices and condiments. We may compare the use of these articles of food
to that of oil in lubricating various parts of a steam-engine. For, as
the oil neither forms part of the heat-supply nor of the force-supply
of the steam-engine, nor is used to replace the worn material of its
structure, yet serves to render the movements of the machine more
equable and effective, so the forms of food we are considering are
neither heat-producing nor flesh-forming, nor do they serve to replace,
to any great extent, the mineral constituents of the body, yet they
produce a sense of refreshment accompanied with renewed vigour. It is
difficult to determine in what precise way these effects are produced,
but no doubt can exist as to the fact that they are really attributable
to the forms of food to which we have assigned them.
Tea, coffee, and cocoa owe their influence on the nervous system to
the presence of a substance which has received the various names of
_theine_, _caffeine_, and _theobromine_. It is identical in composition
with _piperine_, the most important ingredient in pepper. It may be
separated in the form of delicate white, silky crystals, which have a
bitter taste. In its concentrated form this substance is poisonous, and
to this circumstance must be ascribed the ill effects which follow
from the too free use of strong tea or coffee. However, the instances
of bad effects resulting from the use of “the cup which cheers but not
inebriates” are few and far between, while the benefits derived from
it are recognized by all. It has, indeed, been stated that no nation
which has begun to make use of tea, coffee, or cocoa, has ever given up
the practice; and no stronger evidence can be required of the value of
those articles of food.
Of alcoholic liquors it is impossible to speak so favourably. They
are made use of, indeed, almost as extensively as tea or coffee; they
have been made the theme of the poet, and hailed as the emblems of
all that is genial and convivial. Yet there can be little doubt that,
when a balance is struck between the good and evil which have resulted
to man from their use, the latter is found largely to preponderate.
The consideration of these evils belongs, however, rather to the
moralist than to the physiologist. I have here simply to consider
alcoholic liquors as articles of food. There can be little doubt that,
when used with caution and judgment, they afford in certain cases an
important adjunct to those articles which are directly applied to
the reparation of bodily waste. Without absolutely nourishing the
frame, they ultimately lead to this end by encouraging the digestive
processes which result in the assimilation of nutritive articles of
food. But the quantity of alcohol necessary to effect this is far less
than is usually taken even by persons who are termed temperate. It is
also certain that hundreds make use of alcoholic liquors who have no
necessity for them, and who would be better without them. Those who
require them most are men who lead a studious sedentary life; and it
is such men, also, who suffer most from excess in the use of alcoholic
liquors.
It remains that I should make a few remarks on mistakes respecting the
quantity of food.
Some persons fall into the habit of taking an excessive quantity of
food, not from greediness, but from the idea that a large amount of
food is necessary for the maintenance of their strength. They thus
overtax the digestive organs, and not only fail of their purpose, but
weaken instead of strengthening the system. Especially serious is the
mistake often made by persons in delicate health of swallowing—no
other word can be used, for the digestive organs altogether refuse
to respond to the action of the mouth—large quantities of some
concentrated form of food, such as even the strongest stomach could
not deal with in that form. I knew a person who, though suffering
from weakness such as should have suggested the blandest and simplest
forms of food, adopted as a suitable breakfast mutton-chops and
bottled stout, arguing, when remonstrated with, that he required more
support than persons in stronger health. He was simply requiring his
weak digestive organs to accomplish work which would have taxed the
digestive energies of the most stalwart labourer working daily in the
open air for many hours.
On the other hand, a too abstemious diet is as erroneous in principle
as a diet in excess of the natural requirements of the system. A
diet which is simply too abstemious is perhaps less dangerous than
persistent abstinence from the use of certain necessary forms of food.
Nature generally prevents us from injuring ourselves by unwisely
diminishing the quantity of food we take; but unfortunately she is not
always equally decided in her admonitions respecting the quality of
our food. A man may be injuring his health through a deficiency in the
amount either of the heat-forming or of the flesh-forming food which he
consumes, and yet know nothing of the origin of the mischief. It may
also be noted that systematic abstinence, either as respects quantity
or quality of food, is much more dangerous than an occasional fast.
Indeed, it is not generally injurious either to abstain for several
days from particular articles or forms of food, or to remain, for
several hours beyond the usual interval between meals, without food of
any sort. On the contrary, benefit often arises from each practice. The
Emperor Aurelian used to attribute the good health he enjoyed to his
habit of abstaining for a whole day, once a month, from food of all
sorts; and many have found the Lenten rules of abstinence beneficial.
As a rule, however, change of diet is a safer measure than periodical
fasting or abstinence from either heat-producing or flesh-forming
food. It must be noticed, in conclusion, that young persons ought not,
without medical advice, to fast or abstain for any length of time from
the more important forms of food, as serious mischief to the digestive
organs frequently follows from either course.
_OZONE._
The singular gas termed ozone has attracted a large amount of attention
from chemists and meteorologists. The vague ideas which were formed as
to its nature when as yet it had been but newly discovered, have given
place gradually to more definite views; and though we cannot be said
to have thoroughly mastered all the difficulties which this strange
element presents, yet we know already much that is interesting and
instructive.
Let us briefly consider the history of ozone.
Nine years after Priestley had discovered oxygen, Van Marum, the
electrician, noticed that when electric sparks are taken through that
gas, a peculiar odour is evolved. Most people know this odour, since
it is always to be recognized in the neighbourhood of an electrical
machine in action. In reality, it indicates the presence of ozone in
the air. But for more than half a century after Van Marum had noticed
it, it was supposed to be the “smell of electricity.”
In 1840, Schönbein began to inquire into the cause of this peculiar
odour. He presently found that it is due to some change in the oxygen;
and that it can be produced in many ways. Of these, the simplest, and,
in some respects, the most interesting, is the following:—“Take sticks
of common phosphorus, scrape them until they have a metallic lustre,
place them in this condition under a large bell-jar, and half-cover
them with water. The air in the bell-jar is soon charged with ozone,
and a large room can readily be supplied with ozonized air by this
process.”
Schönbein set himself to inquire into the properties of this new gas,
and very interesting results rewarded his researches. It became quite
clear, to begin with, that whatever ozone may be, its properties are
perfectly distinct from those of oxygen. Its power of oxidizing or
rusting metals, for example, is much greater than that which oxygen
possesses. Many metals which oxygen will not oxidize at all, even
when they are at a high temperature, submit at once to the influence
of ozone. But the power of ozone on other substances than metals is
equally remarkable. Dr. Richardson states that, when air is so ozonized
as to be only respirable for a short time, its destructive power is
such that gutta-percha and india-rubber tubings are destroyed by merely
conveying it.
The bleaching and disinfecting powers of ozone are very striking.
Schönbein was at first led to associate them with the qualities of
chlorine gas; but he soon found that they are perfectly distinct.
It had not yet been shown whether ozone was a simple or a compound
gas. If simple, of course it could be but another form of oxygen. At
first, however, the chances seemed against this view; and there were
not wanting skilful chemists who asserted that ozone was a compound of
the oxygen of the air with the hydrogen which forms an element of the
aqueous vapour nearly always present in the atmosphere.
It was important to set this question at rest. This was accomplished by
the labours of De la Rive and Marignac, who proved that ozone is simply
another form of oxygen.
Here we touch on a difficult branch of modern chemical research. The
chemical elements being recognized as the simplest forms of matter,
it might be supposed that each element would be unchangeable in its
nature. That a compound should admit of change, is of course a thing to
be expected. If we decompose water, for instance, into its component
elements, oxygen and hydrogen, we may look on these gases as exhibiting
water to us in another form. And a hundred instances of the sort might
be adduced, in which, either by separating the elements of a compound,
or by re-arranging them, we obtain new forms of matter without any real
change of substance. But with an element, the case, one would suppose,
should be different.
However, the physicist must take facts as he finds them; and amongst
the most thoroughly recognized chemical facts we have this one, that
elementary substances may assume different forms. Chemists call the
phenomenon allotropy. A well-known instance of allotropy is seen in
red phosphorus. Phosphorus is one of the chemical elements; and, as
every one knows, the form in which it is usually obtained is that of a
soft, yellow, semi-transparent solid, somewhat resembling bees’ wax in
consistence, poisonous, and readily taking fire. Red phosphorus is the
same element, yet differs wholly in its properties. It is a powder, it
does not readily take fire, and it is not poisonous.
Ozone, then, is another form of oxygen. It is the only instance yet
discovered of gaseous allotropy.
And now we have to deal with the difficult and still-vexed questions
of the way in which the change from oxygen is brought about, and the
actual distinction between the two forms of the same gas. Schönbein
held that common oxygen is produced by the combination of two special
forms of oxygen—the positive and the negative, or, as he called them,
ozone and antozone. He showed that, in certain conditions of the air,
the atmospheric oxygen exhibits qualities which are the direct reverse
of those which ozone exhibits, and are distinct from those of ordinary
oxygen. In oxygen thus negatived or antozonized, animals cannot live
any more than they can in nitrogen. The products of decomposition are
not only not destroyed as by ozone, but seem subject to preservative
influences, and speedily become singularly offensive; dead animal
matter rapidly putrefies, and wounds show a tendency to mortification.
But the theory of positive and negative forms of oxygen, though still
held by a few physicists, has gradually given way before the advance
of new and sounder modes of inquiry. It has been proved, in the first
place, that ozone is denser than ordinary oxygen. The production of
ozone is always followed by a contraction of the gas’s volume, the
contraction being greater or less according to the amount of oxygen
which has been ozonized. Regularly as the observers—Messrs. Andrews
and Tait—converted a definite proportion of oxygen into ozone, the
corresponding contraction followed, and as regularly was the original
volume of the gas restored when, by the action of heat, the ozone was
reconverted into oxygen.
And now a very singular experiment was made by the observers, with
results which proved utterly perplexing to them. Mercury has the power
of absorbing ozone; and the experimenters thought that if, after
producing a definite contraction by the formation of ozone, they could
absorb the ozone by means of mercury, the quantity of oxygen which
remained would serve to show them how much ozone had been formed, and
thence, of course, they could determine the density of ozone.