Science from an Easy Chair

by Sir E. Ray Lankester

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.

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.)

[Transcriber’s Note: The original image is approximately 2 inches (5cm) high and 3 inches (7.5cm) wide.]