EFFECTS ON ANIMAL AND VEGETABLE LIFE.
As salt is one of the principal constituents of the blood, and as it
is present in the various tissues of the body, and as its ingestion is
necessary for the animal economy, for the maintenance of its health,
and consequently for the due development of the several organs, and the
invigorating effects it exerts over their functional activity, we will
now consider it in the relation it holds to animal and vegetable life.
By the great majority of land animals salt is evidently an article
much relished, for in those districts where salt springs and lakes are
prevalent, many quadrupeds and birds are invariably to be seen.[50]
They frequent these spots in great numbers, and very seldom migrate
to those districts which are deficient in salt, or, if they do, very
speedily return; these animal instincts are indicative that they are
aware of its bracing qualities, and experience the salubriousness of
the atmosphere, which naturally is impregnated with a fair amount of
salt, which has risen through the media of exhalations from the water
or evaporation of the same.
In the Ruminantia the beneficial and, indeed, the salutary action of
salt is remarkably observable, for it counteracts in this class of
animals the deleterious effects of rainy weather, damp pasturage,
and damaged fodder. It also imparts a consistency to the fat, and
renders the meat more palatable and wholesome. All cattle, without an
exception, thrive best if they are supplied with salt; and they will
consume no small quantity. Horses will, on the average, consume daily
six ounces; cows, four ounces, and will, it is said, secrete a larger
quantity of milk, and of a much richer quality, than those from which
salt is usually withheld. Sheep will consume half an ounce daily, and
they are not affected with the rot, as is so frequently the case in
low-lying marshy districts where they drink water in which there are
myriads of the fluke-worm, embryonic and developed, especially after
heavy rains or inundations, as, for instance, a river overflowing its
banks. It is a fact which farmers and graziers should by no means
lose sight of, that these worms are totally destroyed by giving sheep
a certain amount of salt during moist and wet seasons, and in those
localities which are generally in a state of humidity.
In marine animals common salt is a necessary constituent of their
drink, and in fact it is the preserver of their life; but it is
injurious, if not certain destruction, to many fresh-water fish, though
some live both in the sea and fresh water—as the salmon, sturgeon, and
some species of lamprey. The male salmon, on entering the mouths of
rivers in order to spawn, follow the females, and fecundate the ova
which they have deposited in little pools, or kinds of nests. They,
therefore, are hatched in rivers. After the first year they remove to
the sea, and, remaining in it for about two months to ten weeks, return
to fresh water. Such is the alternate fresh and salt-water life of the
salmon, showing us that some fish can live in the sea and breed in
fresh water.
Reptiles and animals of an inferior class are deprived of life by the
action of salt water; and such organisms as the amœba, hydra, rotifer,
and others of a similar grade which we see in stagnant ponds, are
speedily killed if put into water in which salt is dissolved; this is
also the case with earth-worms, snails, and indeed all insects as a
general rule, especially if generated by animal and vegetable decay.
Owing to the antagonism of salt to life produced by putrefaction, it
is frequently rubbed into meat to prevent it from being attacked by
putrescent larvæ; and even if decomposition has commenced, it arrests
for a long time its further progress. We all know what an intense
irritant it is to leeches, and how they immediately vomit if some salt
is sprinkled upon them when they are engorged with blood.
Land shells are rapidly killed by sea-water, and so are their
eggs; this fact has been demonstrated by Darwin, who says: “Their
eggs, at least such as I have tried, sink into it and are killed.”
From experiments performed by Baron Aucapitaine, we find the above
corroborated. He placed in a box, pierced with holes, one hundred land
shells belonging to ten different species, and then immersed it in
sea-water for a fortnight; _only_ twenty-seven recovered.
These experiments are conclusive, and prove that salt destroys life
of an inferior grade, probably owing to the fact that, generally, it
is calculated to produce results of a nature somewhat disposed to
become an annoyance, or even inimical to the vitalisation of superior
organisms, and tends to arrest their progress and due development.
We must remember that these two experiments of Mr. Darwin and Baron
Aucapitaine were with sea-water, consequently the other salts which it
holds in solution (the sulphates of soda and magnesia), and the organic
matter which it contains, very probably hastened the progress.
The Batrachians, a class of animals allied to the reptiles, but
undergoing a peculiar metamorphosis, have an antipathy to salt, and
consequently cannot live in salt water; it is death to them sooner or
later.
We cannot say that reptiles, as a rule, frequent fresh water in
preference to salt, some being found only in sea-water, and in those
parts of the ocean where there is a greater quantity of saline matter
than in others. There is the marine Chelonia, for instance, commonly
known as turtles (Chelones); one sub-group, the common green turtle,
so well known for its palatable qualities, is composed of species
altogether herbivorous, and of gregarious and innocent habits, “These
animals may be seen in herds at the bottom of the sea, quietly browsing
on the weeds growing there. Sometimes they enter the mouths of large
rivers, and are occasionally seen to make their way ashore, apparently
in search of food.”[51] Like the salmon, it is a habitat of both
fresh and sea water, though under different conditions; one frequents
fresh-water for food, the other for breeding. Another sub-group
comprises turtles of carnivorous habits, active, and, when attacked,
fierce; such is the loggerhead turtle and the hawksbill; the latter is
the animal which furnishes the arts with the elegant substance called
tortoise-shell. There is also a genus of carnivorous habits, called the
Sphargis, or coriaceous turtle.
There are likewise the river tortoises (Tryonices), which are
conspicuous tenants of the Ganges, the Euphrates, the Niger, the Nile,
the Mississippi, and the Ohio. These reptiles are next in size to the
turtles, some being three feet long; they are very fierce, and do not
even scruple to attack the young alligators. They live principally on
fresh-water fish and small reptiles; sometimes they will venture into
sea-water in quest of food, though not far, as we may suppose. There
are also the Emydes, which are sometimes called fresh-water tortoises,
sometimes marsh tortoises, which are of many different species. They
haunt lakes, marshes, and small rivers in Asia, Africa, and Australia,
but more particularly America, where the proper habitat is represented.
In the North American rivers there is found the Emysaura serpentina,
which has a large head and crocodilian tail; it feeds on fishes and
small birds. Another species, called Chelys fimbriata, or Matamata,
belongs exclusively to the rivers of Guiana.
We thus see that the Chelonia, which are remarkable for the box-like
case in which most of them are enclosed, are inhabitants of the sea,
while their near relations, the tortoises, are only partially aquatic
in their habits.
Reptiles are therefore neither land, sea-water, nor fresh-water
animals, if we view them as a whole; but if we divide them into orders,
we shall be able to see at once which are fresh-water, which are
terrestrial, and which are inhabitants proper of the sea. Firstly,
there is the Amphibia (doubled-lived), which live and breed in fresh
water, such as rivers, lakes, ponds, and ditches, and which are killed
if put into salt water. Secondly, there is the Ophidia (snake-like
order), which are peculiar to the land, though there is a fresh-water
snake in the East Indies, and which the natives will boldly attack with
sticks. The Sauria (lizards) next claim our attention. The alligator
is a native of North America, and is very abundant in the Mississippi.
It is very seldom seen near the mouths of rivers, and in winter it
buries itself in the mud, and continues in a torpid state till spring.
Then there are the crocodiles, which are natives of Africa, the West
Indies, and America. Their habits are somewhat similar to those of the
alligator, frequenting the creeks of rivers by night in search of food;
they are sometimes seen near the mouths of rivers, but not as a rule.
We have already remarked upon the Testudinata, or the turtle kind.
Reptiles, therefore, either frequent the land or the water; some are
purely aquatic, others purely terrestrial, the remainder are both; one
order is altogether marine, though frequently they are seen on shore,
where they are caught.
Salt water is death to one order, but affords the means of life to
another; to yet another order, with but few exceptions, both salt and
fresh water are deleterious, and, in fact, death; whilst still another
order frequents both elements, just as the chances of obtaining food
may direct them.
Such animals as the hippopotamus, the rhinoceros, the tapir, and the
elephant, and a few others belonging to the Pachydermata, frequent
the banks of rivers and fresh-water lakes, where they wallow in the
mud, and now and then, as fancy takes them, splash about in the water;
but they, like the crocodile, have never been known, as far as I can
gather, to make for salt water, and therefore they are seldom, if ever,
seen near the mouths of rivers, or by the coast.
Salt is therefore not avoided, almost as a rule, either by animals
or birds; and in those districts where salt lakes are situated (to
which interesting fact I have already alluded) are to be invariably
seen, not only great numbers of animals, but large flocks of birds of
different kinds, showing conclusively that they possess an instinctive
preference for those localities where the atmosphere is more or less
filled with saline matter, than for those places where it is entirely
absent. It is but seldom that animals frequent those spots which are
injurious to them; they take good care to avoid them, if possible, and
if they detect anything deleterious, whether it be in the air, soil, or
water, they migrate to more genial quarters; instinct indicates this
necessity, and they accordingly act upon it. It is strange that mere
animal instinct should be superior to human reason, and that animal
sagacity should be more far-seeing than human forethought! Nothing is
more strongly confirmative of this anomaly, if I may call it so, than
the partiality which animals entertain for those districts which abound
with salt lakes, and the antipathy, or utter indifference, with which
some people regard that substance which keeps the body pure, healthy,
and, I may say, clean, and which plays such a highly-important part in
the animal economy.
In the vegetable kingdom salt is by no means an inconsiderable item,
and as an agricultural agent it is most invaluable, though its
operation therein varies in a remarkable degree; in small quantities
it is injurious only to a few plants, while to some it appears to be
beneficial in every way. In moderation it is an excellent manure,
especially if the soil is of a sandy nature; but in large quantities
it is decidedly pernicious to all plants, without an exception, though
unequally so. According to experiments made by Dr. Balfour and other
eminent botanists, it appears that a solution of the chloride of
sodium does not act so deleteriously as solutions of other inorganic
substances, and the same effect is observable with a solution of the
phosphate of soda: the strength of these solutions, we are told, varied
from half a grain to five grains to the ounce of water; the sodium
combined with the chlorine forming the chloride of sodium, and with the
oxygen forming soda; the potassium, combined with the chlorine, forming
the chloride of potassium, and with the oxygen forming potassa. The
combinations take place, according to Johnston, in the living plants
owing to the natural affinities of these inorganic substances.
Darwin writes: “In botanical works, this or that plant is often
stated to be ill-adapted for wide dissemination, but the greater
or less facilities for transport across the sea may be said to be
almost wholly unknown. Until I tried, with Mr. Berkeley’s aid, a few
experiments, it was not even known how far seeds could resist the
injurious action of sea-water. To my surprise I found that out of 87
kinds, 64 germinated after an immersion of 28 days, and a few survived
an immersion of 137 days. It deserves notice that certain orders were
far more injured than others; nine Leguminosæ were tried, and, with
one exception, they resisted the salt-water badly; seven species of
the allied orders, Hydrophyllaceæ and Polemoniaceæ, were all killed
by a month’s immersion. For convenience’ sake, I chiefly tried small
seeds, without the capsules or fruit; and as all these sank in a few
days, they could not have been floated across wide spaces of the sea,
whether or not they were injured by the salt-water. Afterwards I tried
some larger fruits, capsules, etc., and some of these floated for a
long time. It is well known what a difference there is in the buoyancy
of green and seasoned timber; and it occurred to me that floods would
often wash into the sea dried plants or branches with seed capsules or
fruit attached to them. Hence I was led to dry the stems and branches
of 94 plants with ripe fruit, and to place them on sea-water. The
majority sank quickly, but some which, whilst green, floated for a
very short time, when dried floated much longer; for instance, ripe
hazel-nuts sank immediately, but when dried they floated for 90 days,
and afterwards when planted germinated; an asparagus-plant with ripe
berries floated for 23 days, when dried it floated for 85 days, and
the seeds afterwards germinated; the ripe seeds of Helosciadium sank
in 2 days, when dried they floated for above 90 days, and afterwards
germinated. Altogether, out of the 94 dried plants, 18 floated for
above 28 days; and some of the 18 floated for a very much longer
period. So that as 64/87 kinds of seeds germinated after an immersion
of 28 days; and as 18/94 distinct species with ripe fruit (but not all
the same species, as in the foregoing experiment) floated, after being
dried, for above 28 days, we may conclude, as far as anything can be
inferred from these scanty facts, that the seeds of 14/100 kinds of
plants of any country might be floated by sea-currents during 28 days
and would retain their power of germination.”
We have thus sufficient evidence before us to prove that salt or sea
water does not totally destroy the vitality of seeds when they are
in a dry state, that some of them will float for 90 days, and when
planted subsequently will germinate; but that when not dry they will
sink immediately. We may, therefore, justly conclude from the result of
these experiments that salt is not noxious to vegetable life, neither
does it destroy the latent principle of procreation which exists in
them; and that though the process of germination may be retarded, and
kept in a state of abeyance, it is not virtually annihilated, as one
would feel inclined to predict, by the prolonged immersion of seeds in
salt-water, be they dried or fresh.
Darwin’s experiments were afterwards verified, for he states that
subsequently M. Martens tried “similar ones, but in a much better
manner, for he placed the seeds in a box in the actual sea, so that
they were alternately wet and exposed to the air like really floating
plants. He tried 98 seeds, mostly different from mine; but he chose
many large fruits and likewise seeds from plants which live near the
sea; and this would have favoured both the average length of their
flotation, and their resistance to the injurious action of the salt
water. On the other hand, he did not previously dry the plants or
branches with the fruit; and this, as we have seen, would have caused
some of them to have floated much longer. The result was that 18/98
of his seeds of different kinds floated for 42 days, and were then
capable of germination. But I do not doubt that plants exposed to the
waves would float for a less time than those protected from violent
movement as in our experiments. Therefore it would, perhaps, be safe to
assume that the seeds of about 10/100 parts of a flora, after having
been dried, could be floated across a space of 900 miles in width, and
would then germinate. The fact of the larger fruits often floating
longer than the small, is interesting; as plants with large seeds or
fruit which, as Alph. de Candolle has shown, generally have restricted
ranges, could hardly be transported by other means.”
Darwin’s experiments show us that salt or sea water does not entirely
extirpate the life which is dormant in seeds, and those of Martens
prove that seeds may be immersed in sea-water itself and yet retain the
power of germination; and that when dry they may even float for 900
miles, and germinate when planted; developing into plants at the usual
period of time allotted by nature!
In Cheshire it is a custom to let out the water of the salt-springs
after rain, in order to improve the character of the soil and make
it more productive. If we call to mind the preservative properties
of salt and the purifying action which it possesses, with regard to
animal and vegetable substances, we need not at all be surprised at the
above use to which it is put by the agriculturists of Cheshire. The
reader, perhaps, would like to know why it is used after rain. After a
heavy shower, and more especially in the country, every insect leaves
its little secluded habitation: the bee is once more on the wing; the
spider resumes his usual central position in his web; flies of all
sizes buzz here and there in search of food or for more secure homes;
every bush is alive with its usual occupants; the lofty tree is once
more the tenement of song; the caterpillar crawls on his solitary way;
the ant trudges along on the gravel-path; the snail emerges from his
retreat and plods slowly to another home; and the earth-worm raises
itself on the lawn; all with one accord hail the reappearance of
sunshine, and show signs, however feeble, of joy that the rain-cloud
has passed and that the landscape has resumed its beauties, and the sky
its gold and azure. The earth after rain, and particularly in spring
and summer, teems with almost reanimated life, both with that which is
harmless and with that which is hurtful, so that the Cheshire custom
is one which cannot be too highly recommended, for when the soil is
saturated with moisture, a soluble salt like the chloride of sodium,
already in a state of solution, sinks in more rapidly, and permeates
it more thoroughly than if it were merely sprinkled over the surface;
and such insects as are associated with or which live in the earth are
speedily eliminated, or are forced to seek shelter at a greater depth,
where they ultimately die by reason of their inability to obtain their
proper sustenance or the unsuitableness of their new abode.
There is a plant called Halimodendron which only grows in the dry,
naked salt-fields by the river Irtysh, in Siberia; it is a genus
of the Leguminosæ, and has purple flowers. Saltwort, or Salsola,
(_salsus_, salt) is chiefly maritime, and the kelp of our shores is
principally obtained from it. At one time the carbonate of soda was
derived from this kelp or barilla, the ashes being obtained from
burning sea-weeds and a species of Salsola; but now it is almost
invariably made from common salt, by adding sulphuric acid, and so
converting the chloride of sodium into a sulphate, and afterwards, by
combustion with chalk and small coal, resolving it into a sulphide, and
then into a carbonate. It is manufactured on a very large scale, and is
an important staple of commerce. From it is obtained a most important
drug, the bicarbonate of soda, the efficacy of which everyone, more or
less, has once in a lifetime experienced.
This kelp has been put to a fraudulent use, for Sir Robert Christison
tells us that disease has been traced to an impure kind of salt,
in which, when investigated, the hydriodate of soda was detected,
resulting, he says, from an inferior salt obtained from kelp.[52]
In all those districts which are intersected by salt marshes, there is
almost a complete absence of miasmatic effluvia, though, as a natural
consequence, the vegetation is not of that rank luxuriance which is
invariably to be seen in other marsh lands; because, whenever the soil
is in a state of moisture, it is always covered with all kinds of weeds
and useless plants, which altogether stop the growth of those which are
of utility to the agriculturist.
In the case of salt marshes it is the reverse, and the neighbourhood is
perfectly free from those endemic diseases which are prevalent in such
localities as the fen-country, and other similar districts; for the
atmosphere is pure, and the soil comparatively dry, and intermittent
fever is unknown.