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.

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.

Jelly-fishes are often called “sea-nettles,” because of the microscopic poison-bearing threads which they discharge from their skin. These are used to paralyse their prey, and, in a few kinds only, are sufficiently powerful to cause a “stinging” effect when they come into contact with a bather’s skin. Sea-anemones are also armed with these minute threads, and their poison has been extracted and studied. The spines of star-fishes and sea-urchins have a very deadly poison associated with them, which has recently been examined. Among insects we have the bees, wasps, and ants, with their terminal stings; caterpillars, with poisonous hairs; gnats, with poisonous mouth glands. Residents in mosquito-infested countries become “immune” to the poison of gnat-bite, but not to the deadly germs of malaria and yellow fever carried by the gnats. The centipedes have powerful jaws, provided with poison-sacs; the spiders have stabbing claws, fitted with poison-glands. Shell-fish, such as crabs and lobsters, do not possess stings or poison-sacs, but some of the whelk-like sea-snails have poison-glands, which secrete a fluid deadly to other shell-fish. We have already spoken of the poison-spines of fishes; among reptiles it is only some of the snakes which are poisonous, and are known to have poison-glands connected with grooved fangs. Only one kind of lizard—the Heloderm of North America, already mentioned—has poison-glands in its mouth, but it has no special poison-fangs, only small teeth. There is a most persistent and curious popular error to the effect that the rapidly moving bifid tongue of snakes and lizards is a “sting.” It is really quite innocuous. No sting is known among birds, although some have fighting “spurs” on the leg, and “claws” on the wing.

Only the lowest of the mammals or warm-blooded hairy quadrupeds—namely, the Australian duck-mole (Ornithorhynchus) and the spiny ant-eater (Echidna)—have poison-glands and related “spurs,” or stings. They have on the hind-leg a “spur” of great size and strength, which is perforated and connected with a gland which produces a poisonous milky fluid. Recent observations, however, as to the poisonous character of this fluid are wanting. Many mammals have large sac-like glands, which open by definite apertures, in some cases between the toes, in others upon the legs, at the side or back of the head (the elephant), in the middle of the back or about the tail. The fluid secreted by these glands is not poisonous nor acrid, but odoriferous, and seems to serve to attract the individuals of a species to one another. They resemble in structure and often in position the poison-glands of the spurs of the duck-mole and spiny ant-eater.

Many insects produce a good deal of irritation, and even dangerous sores, by biting and burrowing in the human skin, without secreting any active poison. Often they introduce microscopic germs of disease in this way from one animal to another, as, for instance, do gnats, tsetze-flies, and horse-flies, and as do some small kinds of tics. The bites of the flea, of midges, gnats, and bugs are comparatively harmless unless germs of disease are introduced by them, an occurrence which, though exceptional, is yet a great and terrible danger. We now know that it is in this way, and this way only, that malaria or ague, yellow fever, plague, sleeping-sickness, and some other diseases are carried from infected to healthy men. Various diseases of horses and cattle are propagated in the same way. The mere bites of insects may be treated with an application of carbolic acid dissolved in camphor. The pain caused by the acid stings of bees, wasps, ants, and nettles can be alleviated by dabbing the wound with weak ammonia (hartshorn). Insects which bury themselves in the skin, such as the jigger-flea of the West Indies and tropical Africa, should be dug out with a needle or fine blade. The minute creature, like a cheese-mite, which burrows and breeds in the skin of man and causes the affliction known as the itch must be poisoned by sulphurous acid—a result achieved by rubbing the skin freely with sulphur ointment on two or three successive days. A serious pest in the summer in many parts of England is a little animal known as the harvest-man. These are the young of a small red spider-like creature, called Trombidium. They get on to the feet of persons walking in the grass, and crawl up the legs and burrow into the tender skin. Benzine will keep them away if applied to the ankles or stockings when they are about, and will also destroy them once they have effected a lodgment.

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