them; usually it is necessary to touch or to eat portions of a plant
before it can exert any poisonous effect. The eighteenth-century story
of the upas-tree of Java, which was fabled to fill a whole valley with
its poisonous emanation, and to cause the death of animals and birds at
a distance of fifteen miles, is now known to be a romantic invention.
The tree in question is merely one having a poisonous juice which was
extracted and used by the wilder races of Java as an arrow poison. It is
stated that one of the stinging-nettles of tropical India has such
virulent poison and such an abundance of it in the hairs on its
surface, that explorers have been injured by merely approaching it, the
detached hairs probably floating in the air and getting into the eyes,
nose, and throat of any one coming near it. The poison of the poisonous
stings of both plants and of animals has been to some extent examined of
late years. It is a curious fact that there are proportionately few
plants which sting as compared with the number and variety of animals
which do so. On the other hand, there are an enormous number of plants
which are poisonous to man when eaten by him, but there are very few
animals which are so.
It will be of interest to my readers to know that I received, in
consequence of the publication of the foregoing account of the
“Poison-vine” or “Poison-ivy,” more than fifty letters and boxes
containing leaves. At Kew Gardens nearly a hundred applications were
made with a request for the identification of leaves. The proportion of
cases in which leaves of true poison-ivy (_Rhus toxicodendron_) were
sent to me seems to be the same as that which they observed at Kew—only
two samples of the leaves sent to me were those of the true poison-ivy.
Hence we may conclude that the plant has not been very largely
introduced in this country, and probably there are not many hundred
cases existing in England of the painful malady which it can, in certain
people, produce. I have, however, received information of several
instances of this poisoning from different parts of the country, which
are either now under treatment or have been cured, and in some cases the
poison-ivy has been discovered as the cause, owing to the description
which I published. It is certainly true that the illness caused by this
plant only attacks a small proportion of those who handle it, and it is
possible that the plant is more virulent at some seasons and in some
soils than in others. In the United States, even in the neighbourhood of
New York, it is a real danger, and is recognised as such, but as appears
from a letter which I quote below, the reason of the dread which the
“poison-ivy” excites in the States depends on the fact that it is not
there a mere garden plant, but grows wild in great abundance in the
woodlands frequented by holiday-makers and lovers of natural forest and
lakeside wilderness. The poisonous nature of the allied species of
_Rhus_ used for the manufacture of “lacquer” or varnish is recognised by
the Japanese and others who prepare this product and have to handle the
plant—they wear gloves to protect the hands.
As showing what kind of trouble the “poison-ivy” and “poison-oak”
(another kind of _Rhus_ or _Sumach_) give in the United States, I will
quote a letter I have received from an American lady well known in
London society. She says: “I have known, suffered, and struggled against
the poison-ivy in America from my earliest years, when my poor mother
lay for days with blinded and swollen eyes, having gathered it
inadvertently. The ‘poison-ivy,’ as we call it, is a curse to country
life, outside the purely artificial and cultivated gardens, and even
there it creeps in insidiously.” She describes a beautiful farm property
on Lake Champlain, on the Canadian border, where she and her family
would spend many weeks in summer in order to enjoy the delights of
complete seclusion in wild, unspoilt country: “The one and only drawback
to the place was,” she writes, “the inexhaustible quantity of
poison-ivy. Our first duty had been to teach my two daughters and their
governess how to distinguish and avoid contact with it. The one and only
rule was that the poison-ivy has the clusters of three leaflets (the
middle leaflet with a longer stalk, _E.R.L._), whereas the woodbine (not
the English woodbine, which is a convolvulus, _E.R.L._), or, as you
call it, ‘Virginian creeper,’ has five leaflets in a cluster. Every path
which we used frequently and necessarily, such as the path to the
boat-house, and to the cove where the bathing-house stood, we kept
cleared of the _Rhus_ for a sufficient width, but in the woods eternal
vigilance was the price of safety. To uproot and burn is the only way to
destroy it, but, of course, that involves danger to the one who does the
work, because contact with the spade used, and with the garments which
touched the ivy, might communicate the poison. The farmer and the
countryfolk about declared that the fumes from the burning plant could
and did poison those who breathed them. We used to turn a flock of sheep
into the most used parts. They prefer the poison-ivy to grass, and
greedily eat down every leaf within reach in hedge or path. But that, of
course, was a mere temporary safety, as the plant is most tenacious of
life. I personally had a most grievous experience one summer. I can only
suppose that my dress, though very short for wood and hill walking,
brushed over the poisonous plant, and then, when I undressed, came into
contact with my skin. Both legs became covered with the eruption,
eventually developing pustules, and the agony of itching, burning, and
smarting was indescribable. The first remedy applied is usually a
frequent use of baths of some alkali, generally common soda. With me it
was altogether inadequate, and the doctor carefully covered the affected
parts with a thick layer of bismuth, and bandaged them, so as to exclude
all air. But it took weeks to cure me. A very serious result in many
cases is that there is a recurrence of the itching for several years.”
XII
POISONS AND STINGS OF PLANTS AND ANIMALS
To give an account of poisonous plants would require a whole volume.
Among plants of every degree and kind are many which produce special
chemical substances which are more or less poisonous, and yet often of
the greatest value to man when used in appropriate doses, though
injurious and even deadly if swallowed in large quantity. Plants are
laboratories which build up in a thousand varieties wonderful chemical
bodies, some crystalline, some oils, some volatile (as perfumes and
aromatic substances), some brilliantly coloured (used as dyes), some
pungent, some antiseptic, some of the greatest value as food, and some
even digestive, similar to or identical with those formed in the stomach
of an animal.
Man, the chemist, every year is learning how to produce in his own
laboratories, from coal and wood refuse, many of these bodies, so as to
become to an ever-increasing extent independent of the somewhat
capricious and costly services of the chemists supplied by nature—the
plants. In a recent exhibition there was a case showing on one side the
various essential oils used to make up a flask of eau-de-Cologne, and
specimens of the plants, flowers, leaves, and fruits from which they
are distilled. On the other side of the case was a series of bottles
showing the steps in the process by which the modern chemist
manufactures from coal-tar and coker-butter the same bodies which give
value to the vegetable extracts, and there was finally a bottle of what
is called “synthetic eau-de-Cologne”—that is, eau-de-Cologne put
together from the products manufactured by the human, instead of the
vegetable, chemist.
Whilst man has learnt to avoid swallowing poisonous plants, although
occasionally blundering over pretty-looking berries and deceptive
mushrooms, he has had little to fear in that way from animals. To a
small degree this is due to the fact that only parts of animals are
eaten by man, and those very generally are cooked before being eaten,
the heating often sufficing to destroy substances present in flesh,
fish, and fowl which would be poisonous if taken raw. But, as a matter
of fact, animals do not generally protect themselves from being eaten,
as plants largely do, by developing nasty or poisonous substances in
their flesh, though some do. They fight rather by claws, teeth, and
poison glands therewith connected, or else escape by extra quick
locomotion, a method not possible to plants. Many insects (butterflies,
beetles, and bugs), however, produce nasty aromatic substances which
cause animals like birds and lizards to reject them as food. The toad
and the salamander both produce a very deadly poison in their damp, soft
skins, which causes any animal to drop them from its mouth, and to
regret “bitterly” the attempt to swallow them. The frog has no such
poison in its skin, but can jump out of harm’s way. The strong yellow
and black marking of the European salamander is what is called a
“warning” coloration, just as is the yellow and black outfit of the
poisonous wasp. Animals learn to leave the yellow and black livery
untouched, and the creatures so marked escape the injury which would be
caused them by tentative bites.
There is a curious variation as to susceptibility on the part of man to
poison in the flesh of fishes and shell-fishes when taken by him as
food. The word “idiosyncrasy” is applied to such individual
susceptibility, and is, of course, applicable to the susceptibility
shown by some persons to the poison of the American poison-vine,
described in the last article, and of others to acute inflammation from
the dust of hayfields. Some persons cannot eat lobster, crab, or oysters
or mussels without being poisoned in a varying degree by certain
substances present in those “shell-fish” even when cooked. Often a
“rash” is caused on the skin, and colic. Others, again, cannot eat any
fish of any kind without being poisoned in a similar way, or possibly
are only liable to be poisoned by grey mullet or by mackerel. The most
curious cases of this individual variability are found in the rash and
fever caused by the vegetable drug quinine in rare instances, and the
violent excitement produced in some persons by the usually soporific
laudanum. All such cases have very great interest as showing us what a
small difference separates an agreeable flavour or a valuable medicine
from a rank poison, and how readily the chemical susceptibility of a
complex organism like man may vary between toleration and deathly
response, without any concomitant indication of such difference being
apparent (in our present state of knowledge), in two individuals, to one
of whom that is poison which to the other is meat. They also furnish a
parallel to that marvellous conversion of “toxin” into “anti-toxin,” in
consequence of which the blood of an animal injected with small,
increasing doses of deadly snake poison or diphtheria poison becomes an
antidote to the same poison taken into the blood of an unprepared
animal.
There is, over and above these special cases of fish foods which are
tolerated by some and are poison to others, a whole series of fishes
which cannot be eaten by any one without serious poisoning being the
result, even when the fish are carefully cooked. Happily, these fishes
are rarely, if ever, caught on our own coasts. They produce, when even
small bits are eaten, violent irritation of the intestine, and death,
the symptoms resembling in many respects those of cholera. The curious
bright-coloured, beaked fish of tropical seas and coral reefs, with two
or four large front teeth and spherical spine-covered bodies, and the
trigger fish of the same regions, are the chief of these poisonous fish.
But there is a true anchovy on the coast of Japan, and a small herring
in the West Indies, and a goby on the Indian coast (Pondicherry), all of
which are deadly poison even when cooked; and there are many others. So
one has to be careful about fish-eating in the remoter parts of the
world. The poisons of these fish with poisonous flesh have not been
carefully studied, but they seem to resemble chemically the poisons
produced by certain putrefactive microbes.
Let us now revert to the more special subject of poisonous stings. Every
one knows that although it is unpleasant to be pricked by the little
spines on the leaf of a thistle, it is not the same unpleasantness as
being “stung” by a nettle. There is no poison in the thistle. The hairs
which beset the leaves of the common nettle are firm, but brittle and
hollow; they break off in the skin, and a poison exudes from their
interior. Under the microscope—and it is quite easy to examine it with
a high power—the hollow nettle hair is seen to be partly occupied by
living protoplasm—a transparent, viscid substance which shows an active
streaming movement, and has embedded in it a dense kernel or nucleus
(see Fig. 15 _bis_). It is, in fact, a living “cell,” or life unit. The
space in the cell not occupied by protoplasm is filled with clear
liquid, which contains the poison. This has been examined chemically by
using a large quantity of nettle hairs, and is found to contain formic
acid—the same irritating acid which is secreted by ants when they
sting, whence its name. But later observations show that the juice of
the nettle hair contains also a special poison in minute quantities, an
albuminous substance, which resembles that contained in the poison-sacs
at the base of the teeth of snakes.
In tropical regions there are nettles far more powerful than that of our
own country. The one called _Urtica stimulans_, which is found in Java,
and that called _Laportea crenulata_, found in Hindostan, when bruised
emit an effluvium which poisonously affects the eyes and mouth, and if
handled produce convulsions and serious swelling and pain in the arms,
which may last for three or four weeks, and in some cases cause death.
They are not unknown in the hothouses of our botanical gardens, and
young gardeners are sometimes badly stung by them. There are other
plants provided with poisonous stinging hairs besides the true nettles
or _Urticaceæ_, though they are not numerous. The American plants called
_Loasa_ sting badly, so do some of the Spurges (_Euphorbiaceæ_), and
some _Hydrophylleæ_.
The Chinese primrose (_Primula obconica_), lately introduced into
greenhouses, has been found to be almost as injurious as the
poison-vine. Its effects, of course, are limited to a much smaller group
of sufferers. And it is worth while, in connection with poisoning by
primula and the poisoning by _Rhus toxicodendron_ of only certain
individuals predisposed to its influence, to point out that the malady
known as hay fever seems to be similar in its character to these
vegetable poisonings. It is, of course, well known that only certain
individuals are liable to the more violent and serious form of hay
fever. It is not at all improbable that this irritation of the air
passages, often attributed to the mechanical action of the pollen of
grass and other plants—really is due to minute quantities of a poison
like that of the poison-vine, present in the pollen of some hay plant
yet to be suspected, tried, and convicted.[2]
With regard to a poisonous action at a distance being possibly exerted
by plants, we must not overlook the effects of some perfumes discharged
into the air by flowers. Primarily such perfumes appear to serve the
flowers by attracting to them special insects, by whose movements and
search for honey in the flowers the pollen of one is conveyed to another
and fertilisation effected. Human beings are sometimes injuriously
affected by the heavy perfume given out by lilies and other flowers,
headache and even fainting being the result. No instance is known of
serious injury or death resulting in the regions where they grow from
the overpowering perfume of such flowers. But that admirable
story-teller, Mr. H. G. Wells, has made a legitimate use of scientific
possibilities in imagining the existence of a rare tropical orchid which
attracts large animals to it by its wonderful odour. The effects of the
perfume are narcotising; the animal, having sniffed at the orchid, drops
insensible at the foot of the tree trunk on which the orchid grows. Then
the orchid rapidly, with animal-like celerity, sends forth those smooth
green fingers or “suckers,” which you may see clinging to the pots and
shelves on which an orchid is growing. As they slowly creep, in their
growth, over the poisoned animal, they absorb its life’s blood
painlessly and without disturbing the death-slumber of the victim. Mr.
Wells supposes a retired civil-servant, with feeble health and a passion
for orchids, to have purchased an unknown specimen, which, after some
months of nursing, is about to blossom in the little hothouse of his
suburban home. He goes quietly and alone one afternoon, when his
housekeeper is preparing his tea, to enjoy the first sight and smell of
the unknown flower, and is found, some three hours later, lying
insensible before the orchid, which is giving out an intoxicating odour,
and is looking very vigorous and wicked. A blood-red tint pervades its
leaves and stalks, and it has already pushed some of its finger-like
shoots round the orchid-lover’s neck and beneath his shirt front. When
they are pulled away a few drops of blood flow from the skin where the
absorbent shoots had applied themselves. The victim recovers.
When we take a survey of the “stings” and poison-fangs and spurs of
animals, we find a much greater abundance and variety of these weapons
than in plants. They serve animals not only as a means of defence, but
very often for the purpose of attacking and paralysing their prey. We
have to distinguish broadly between (_a_) gut-poisons and (_b_)
wound-poisons. The slimy surface of the skin and the juices of animals
are often poisonous if introduced into wounds, but harmless if
swallowed, though in the toad and salamander the skin contains a poison
which acts on the mouth and stomach. Thus the blood of the eel is
poisonous to higher animals if injected beneath the skin, though not
poisonous when swallowed. Pasteur found that the saliva of a healthy
human baby a few weeks old produced convulsions when injected beneath
the skin of a rabbit. The fluid of the mouth in fishes (_Muræna_), in
some lizards (_Heloderma_), and some warm-blooded quadrupeds, like the
skunk, is often poisonous, and is introduced into the wound inflicted by
a bite. The elaboration of a sac of the mouth-surface secreting a
special quantity of poison to be injected by aid of a grooved tooth,
such as we find in poisonous snakes, is only a mechanical improvement of
this more general condition. The same general poisonous quality is found
in the slime of the skins of fishes which have spines by means of which
poisonous wounds are inflicted (sting-rays). And here, too, an
elaboration is effected in some fishes in which a sac is provided for
the accumulation of the poison, and a specially grooved spine, to convey
the poison into the wound inflicted by it. A common fish on our coasts,
the weever (probably the same word as viper), is provided with grooved,
stinging spines, but no special poison-sac. Some of the poison-carrying
spines support the front portion of the dorsal fin, which is of a deep
black colour, a striking instance of the warning coloration which
poisonous animals often possess.
The poison introduced into wounds by the spines or fangs of animals is
essentially similar to that of nettle hairs; it has the effect of
paralysing and of producing convulsions. It is a remarkable fact that
formic acid often in insects accompanies the paralysing poison—as it
does in the nettle—and produces intense pain and irritation, which the
more dangerous nerve-poison does not. Immunity to a given wound-poison
may be produced by the injection of doses of it, at first excessively
minute, but gradually increased in quantity. A remedial “anti-toxin” is
thus prepared from the blood of immunised animals, which is used as a
cure or as a protection by injecting it into other animals exposed to
bites or wounds conveying the particular poison by the use of which the
anti-toxin was produced. Bee-keepers who have often been stung become
in many cases immune, and do not suffer from bee-sting. Men who in
France pursue a business as viper-catchers, are said to become immune to
viper’s poison in the same way. Snakes and scorpions are but little, if
at all, affected by their own poison when it is injected into them. This
appears to be due to the fact that the poison-producing animal is always
absorbing into its blood very minute doses of the poison which it has
elaborated and stored up in its poison-sac connected with the
poison-gland. This small quantity of poison continually absorbed is
continually converted into an anti-toxin—just as happens when a horse
is treated with doses of snake-poison to prepare the remedial anti-toxin
for use in cases of snake-bite, or with diphtheria-poison in order to
prepare the diphtheria anti-toxin now so largely used. The anti-toxin is
a substance very closely similar in chemical constitution to the toxin
by the conversion of which it is formed in the blood. Its action on the
toxin (or essential poisonous substance of the venom) appears to be a
very delicate and slight chemical disturbance of the constitution of
that chemical body. Yet it is enough to cause the injurious quality of
the toxin to be suddenly and completely abrogated, although from the
point of view of chemical composition it is only, as it were, shaken or
given a twist! Such great practical differences in the action on living
creatures of chemical bodies having themselves so subtle a difference of
chemical structure as to almost defy our powers of detection, are now
well known.
[Illustration: FIG. 15.—Drawing from life of the desert scorpion
(_Buthus australis_, Lin.), from Biskra, N. Africa, of the natural size.
(From Lankester, _Journ. Linn. Soc. Zool._, vol. xvi. 1881.)]
I made some experiments a few years ago on the poison of scorpions,
which were published by the Linnæan Society. I obtained live
scorpions—a beautiful citron-coloured kind, of large size—from Biskra,
in Algeria (Fig. 15). The poison-gland and sac are double, and contained
in the last joint of the tail, which is swollen, and ends in a splendid
curved spine or sting. The scorpion carries its tail raised in a
graceful curve over its back, and strikes with the sting by a powerful
forward stroke. One can seize the tail by the last joint but one, and
thus safely hold the animal, and see the poison exude in drops from the
perforated sting. I found that if I pressed the sting thus held into the
scorpion’s own body, or into that of another scorpion, no harm resulted
to the wounded animal, although plenty of the poison entered the little
wound made by the sting. A large cockroach or a mouse similarly wounded
by the sting was paralysed, and died in a few minutes. It is a custom in
countries where scorpions abound, and are troublesome, and even
dangerous to human life, for the natives to make a circle of red-hot
charcoal, and to place a large scorpion in the centre of the enclosed
area. The scorpion, it is stated, runs round inside the circle, and,
finding that escape is impossible, deliberately drives its sting into
its back, and so commits suicide. My experiments showed that the
scorpion could not kill itself in this way, as its poison does not act
on itself. Moreover, it has been shown by Professor Bourne, of Madras,
that although scorpions constantly fight with one another, they never
attempt to use their stings in these battles, but only their powerful,
lobster-like claws. The stings would be useless, and are reserved for
their attacks on animals susceptible to the poison. I also found the
ground for the belief that the scorpion kills itself when enclosed in a
fiery circle. Incredible as it may appear in regard to such denizens of
the hot regions of the earth, both the desert scorpion and the large
dark-green Indian scorpions actually faint and become motionless and
insensible when exposed for a few minutes to a temperature a little
above that of the human body. This was carefully ascertained by using an
incubator and a thermometer. The scorpion in the fiery circle lashes
about with its sting, and then suddenly faints owing to the heat. If
removed from the heat it recovers completely; but, of course, when it is
supposed to have committed suicide, no one takes the trouble to remove
it. I made, several times, the actual experiment of placing a large
active scorpion within a ring-like wall, a foot in diameter, formed by
live coals. The scorpion never stung itself. On one occasion it walked
out over the coals, and on other occasions, after lashing its tail and
running about, fainted, and became motionless.