CHAPTER XVIII.

_VENOMS IN THE ANIMAL SERIES_ (_continued_).

3.--_BATRACHIANS. LIZARDS. MAMMALS._

A.--Batrachians.

By the ancients the venom of _salamanders_ and _toads_ was dreaded as much as the most terrible poisons. These animals, however, are not very formidable, since they are devoid of inoculatory organs; their poison-apparatus is localised exclusively in the parotids and the skin. It is represented simply by more or less confluent glands in the form of sacs, secreting a viscid mucus, which has a nauseous odour and is highly toxic, even to animals of large size.

The salamander belongs to the Order _Urodela_, which is characterised by the persistence of the tail. Its body is heavy and thickset, and the flanks and the sides of the tail exhibit a series of glandular crypts, which secrete venom.

“The mucus which flows from the mouth, and resembles milk, eats away human hair,” wrote Pliny; “the spot moistened by it loses its colour, which subsequently returns. Of all venomous animals the salamander is the most terrible; it is capable of annihilating whole nations by poisoning the vegetation over a vast area. When the salamander climbs a tree all its fruit is poisoned, and those who eat of it die as surely as if they had taken aconite. Moreover, if bread be baked with wood touched by the animal, it is dangerous, and may occasion serious disorders. If the naked foot be defiled with the saliva of this creature, the beard and hair soon fall out. Sextius says that a salamander, preserved in honey, after the removal of the entrails, head, and limbs, acts as a stimulant if taken internally.”

In ancient Rome, and also in Mediæval France, it was believed that the most furious fire could be extinguished simply by contact with one of these animals; charlatans sold the inoffensive salamander, which, if cast into the most terrible conflagration, was bound, they declared, to arrest its disastrous progress!

The explanation of this superstition is furnished by Duméril, who writes: “On being placed in the middle of burning charcoal, these victims of so cruel a curiosity, when put to the test, instantly allowed to exude from the many pores with which their skins are riddled a slimy humour, sufficiently abundant to form a viscid layer over that part of the glowing charcoal with which the animals were in contact. Since this surface, being no longer exposed to the air, immediately became quite black, it was supposed to be extinguished; but the salamanders sustained such severe burns that they soon succumbed.”[148]

The principal species of salamanders are:--

_Salamandra atra_ (Black Salamander), which is found in the Alps and the mountains of Central Europe, close to the snow-line, and up to an altitude of 3,000 metres.

_Salamandra maculosa_ (Spotted Salamander, fig. 121), distributed throughout almost the whole of Europe, and also found in North Africa.

_Triton cristatus_ (Crested Newt), likewise common all over Europe.

_Triton marmoratus_ (Marbled Newt, fig. 122), which is met with in damp and dark places, in Portugal, Spain, South and Central France, and as far north as the Forest of Fontainebleau.

_Cryptobranchus japonicus_ (Great Japanese Salamander, fig. 123), which often exceeds 1 metre in length, and has a clumsy body covered with large warts, and an enormous head, broad behind and flattened in front.

This giant salamander is now confined to a few provinces in the centre of Japan, between long. 34° and 36°, in damp, shady places, from 200 to 800 metres above sea-level. It is eaten by the Japanese, who also use it as a remedy for, or prophylactic against, contagious disorders. By nature it is extremely sluggish, but tries to bite when irritated, and then covers itself copiously with slime.

The venom secreted by salamanders evidently serves to protect these creatures against their enemies. So long ago as 1866, Zaleski[149] isolated from it a substance soluble in alcohol, insoluble in ether, and with a very strong alkaline reaction, to which he gave the name _salamandarin_. This substance, which is better known to-day as _salamandrine_, has been studied afresh by A. Dutartre,[150] Phisalix and Langlois,[151] and subsequently by Edwin and S. Faust.[152]

The action of this poison on the frog is characterised by a period of violent convulsions, with general tetanic crises, followed by a period of paralysis, with arrest of respiration and complete muscular relaxation. According to the quantity of poison absorbed, this paralytic period may be followed by death, with arrest of the heart in diastole, or else by return to life, with more or less acute recurrence of convulsions.

S. Faust prepares salamandrine by pounding up whole salamanders in a small quantity of physiological saline solution. The thick pulp obtained in this way is filtered. One cubic centimetre of the filtrate, taken as a unit, contains about 5 decimilligrammes of active substance, which can be purified by treating the filtrate with alcohol, which dissolves the salamandrine and precipitates all the proteic substances that give biuret reaction. The salamandrine thus freed from proteins is saturated with sulphuric or phosphoric acid, when there is formed a crystallisable salt, which is washed and dried. This salt is soluble in alcohol and in water. Its chemical composition is as follows:--

C^{52}H^{80}Az^4O^2 + H^2SO^4.

The toxicity of this substance is such that from 7 to 9 decimilligrammes per kilogramme represent the lethal dose for dogs, when injected subcutaneously. The lethal dose for the rabbit is still smaller. It produces convulsive phenomena, followed by arrest of respiration. The administration of chloral to the subjects of the experiment, either preventively or immediately after the poison, prevents the latter from taking effect. Besides salamandrine, S. Faust has isolated a second alkaloid, _salamandridine_, which, as a sulphate, corresponds to the formula (C^{20}H^{31}AzO)^2 + H^2SO^4, crystallises in rhombic prisms, and is soluble with difficulty in water. The only difference between the two alkaloids is formed by a methylpyridic group, and both are derivatives of quinoline. They must therefore be considered as identical with the exclusively vegetable alkaloids.

S. Faust concludes from his physiological investigations that salamandrine takes effect upon the central nervous system, especially upon the respiratory centres. It is a convulsion-producing poison, comparable to picrotoxin, but its effects differ from those of the latter substance in that the convulsions are accompanied by tetanic spasms.

The venom of the Japanese Salamander (_Cryptobranchus japonicus_) has formed the subject of studies by Phisalix.[153] This investigator has shown that this venom, which is highly soluble in water and in glycerine, is very unstable; alcohol and heating for twenty minutes at 60° C. are sufficient to destroy it. When inoculated into frogs it produces œdema and hæmorrhage; if injected into warm-blooded animals it causes necrosis. In sufficiently strong doses it kills by arresting respiration. Its effects strongly resemble those produced by VIPERINE venoms. This venom, if attenuated by being heated at 50° C. and injected into mammals, vaccinates them and leads to the formation in their blood of antitoxic substances, which are capable of preventing intoxication by salamander-venom, and, curiously enough, also confer immunity against viper-venom and the serum of the common snake.

_Toads_ are easy to distinguish from frogs owing to their squat and clumsy shape, and to the mass of glands with which each side of the neck and a more or less extensive portion of the body is furnished in these animals. According to G. A. Boulenger, the number of known species amounts to seventy-six, which are found in the Old and New Worlds, but have no representatives in Australia. The species that are the most common, and most interesting from the point of view of their venoms, are:--

The Common Toad (_Bufo vulgaris_), in which the skin, which is very thick and rugose, is covered on the back with large rounded tubercles with reddish summits. This species is a great destroyer of insects, and, as such, is very useful to agriculturists.

The Natter-Jack (_Bufo calamita_), in which the digits are palmate at the base. When irritated it contracts its skin and covers itself with a white frothy exudation, which gives off an odour of burnt powder.

The Green Toad (_Bufo viridis_), which is especially abundant in Southern Europe, the Levant, and North Africa.

The Musical Toad (_Bufo musicus_), a species distributed throughout North America as far south as Mexico, and in which the back is covered with pointed conical tubercles resembling spines.

The Brown Pelobates (_Pelobates fuscus_), common in the neighbourhood of Paris, the skin of which is almost entirely smooth. Although it appears to be nearly destitute of glands, this animal secretes a very active venom, which has a penetrating odour and kills mice in a few minutes, producing vomiting, convulsions, and tetanic spasms of the muscles.

The toxicity of the venom of toads was long ago demonstrated by the experiments of Gratiolet and Cloëz.[154] It is manifest only in the case of small animals, and in man merely produces slight inflammation of the mucous membranes, especially of the conjunctiva.

That this venom preserves its toxic properties for more than a year in the dry state was shown by Vulpian, and satisfactory studies of its composition and physiological action have been made by Fornara,[155] G. Calmels,[156] Phisalix and Bertrand,[157] Schultz,[158] Pröscher,[159] and S. Faust.[160]

Toad-venom was prepared by Phisalix and Bertrand in the following manner: Holding the head of one of these batrachians under water, they expressed the contents of the parotid glands with the fingers or with a pair of forceps. They repeated the same operation with a second, and then with a third toad, until they had sufficiently impregnated the water, which serves to dissolve the venom. In this way they obtained an opalescent, acid liquid, which they filtered with a Chamberland candle under a pressure of from four to five atmospheres. There remained on the filter a yellowish substance, with a highly acid reaction and partly soluble in ether and chloroform, while there passed through the pores a clear, reddish, and slightly acid liquid, which on being evaporated left behind a greyish-white precipitate. This precipitate was separated by filtration, washed in water, and redissolved in absolute alcohol or chloroform. The albuminoid matters were thus separated, and the liquid, after being rendered limpid by filtration, was evaporated away. The substance obtained in this way represents one of the two active principles of the venom. It acts on the heart of the frog, and arrests it in systole. It assumes the appearance of a transparent resin, the composition of which roughly corresponds to the formula C^{119}H^{117}O^{25}. It is the _bufotalin_ of Phisalix and Bertrand, and is probably identical with that obtained by S. Faust, the formula of which, according to the latter author, is said to be C^{11}H^{23}O^{5}.

Bufotalin is readily soluble in alcohol, chloroform, acetone, acetate of ethyl, and acetic acid. When water is added to a solution of it in alcohol it is precipitated, giving a white emulsion, which has a very bitter taste.

From the aqueous extract whence the bufotalin has been separated, it is possible to separate a second poison, which acts on the nervous system and causes paralysis. In order to obtain it in a pure state, the extract is treated with alcohol at 96° C., filtered and distilled; the residue dissolved in water is defæcated with subacetate of lead and sulphuretted hydrogen. The solution thus obtained is successively exhausted with chloroform to extract the cardiac poison, and with ether, which removes almost the whole of the acetic acid. The second neurotoxic principle, called _bufotenin_, remains in the residue of the solution after being evaporated _in vacuo_.

Toad-venom, therefore, contains two principal toxic substances: _bufotalin_, which is of a resinoid nature, soluble in alcohol, but scarcely soluble in water, and is the _cardiac poison_; and _bufotenin_, which is readily soluble in those two solvents, and is the _neurotoxic poison_.[161]

Pröscher, on the other hand, has extracted from the skins of toads a hæmolytic substance, termed by him _phrynolysin_, which possesses all the properties of a true toxin and is not dialysable. It is obtained by pounding the skins with glass powder in physiological serum.

Phrynolysin dissolves the red corpuscles of the sheep very rapidly, and (in order of sensitiveness) those of the goat, rabbit, dog, ox, fowl, and guinea-pig. The red corpuscles of the pigeon, frog, and toad are scarcely affected. When heated at 56° C. it loses its properties. By the ordinary methods of immunisation it is possible to obtain a very active antilysin.

There is, therefore, a very close analogy between the venoms of _toads_ and _salamanders_. These highly complex substances are composed of mixtures of poisons, some of which are in all respects analogous to the vegetable alkaloids, while others are closely related to the microbic toxins and snake-venoms.

In the spawning season the cutaneous glands of the male toad are gorged with venom, while those of the female are empty. Phisalix[162] has shown that at this period the venom of the female is accumulated in the eggs, which, if extracted from the abdomen at the moment of oviposition and dried _in vacuo_, give off in chloroform a product that has all the toxic properties of cutaneous venom (bufotalin and bufotenin). No trace of this poison is to be found in the tadpoles.

B.--Lizards.

The Order LACERTILIA includes only a single venomous species, which belongs to the family _Lacertidæ_, and is known as the _Heloderm_ (_Heloderma horridum_, fig. 124). It is a kind of large lizard, with the head and body covered with small yellow tubercles on a chestnut-brown ground. It sometimes exceeds a metre in length, and its habitat is confined to the warm belt extending from the western slope of the Cordilleras of the Andes to the Pacific. It is met with especially in the vicinity of Tehuantepec, where it inspires the natives with very great dread. It is a slow-moving animal, and lives in dry places on the edges of woods. Its body exhales a strong, nauseous odour; when it is irritated, there escapes from its jaws a whitish, sticky slime, secreted by its highly developed salivary glands. Its food consists of small animals. Its bite is popularly supposed to be extremely noxious, but, as a rule, the wound, though painful at first, heals rapidly. Sumichrast caused a fowl to be bitten in the wing by a young individual, which had not taken any food for a long time. After a few minutes the parts adjacent to the wound assumed a violet hue; the bird’s feathers were ruffled; a convulsive trembling seized its entire body, and it soon sank to the ground. At the end of about half an hour it lay stretched out as though dead, and from its half-open beak there flowed a sanguinolent saliva. There was no movement to give any sign of life, except that from time to time a slight shiver passed through the hinder part of its body. After two hours, life seemed gradually to return, and the bird picked itself up and crouched on the ground, without, however, standing upright, and still keeping its eyes closed. It remained thus for nearly twelve hours, at the end of which time it once more collapsed, and expired.

A large cat which Sumichrast caused to be bitten in the hind leg did not die, but immediately after being bitten the leg swelled considerably, and for several hours the cat continued to mew in a way that showed that it was suffering acute pain. It was unable to stand, and remained stretched out on the same spot for a whole day, unable to get up, and completely stupefied.

Interesting observations on the _Heloderm_ have been made by J. Van Denburgh and O. B. Wight. The saliva of this lizard was found to be highly toxic at certain times, and harmless at others. When injected subcutaneously it produces various effects, such as miction, defæcation, and abundant salivation, with accelerated respiration followed by vomiting. The animal drinks with avidity, and remains lying down, in a very depressed condition. Death finally supervenes, from arrest of respiration and also of the heart’s action. The poison likewise acts upon the arterial tension, which falls very rapidly and very markedly. The sensory nerves are also attacked; irritability is at first increased, then diminished, and at last entirely lost. These changes take place from behind forwards, and from the periphery to the centre. The coagulability of the blood is at first intensified and then lessened, as when acted upon by VIPERINE venom (H. Coupin).[163]

C.--Mammals.

The only mammal that can be considered to be provided with a poison-apparatus belongs to the Order _Monotremata_, and is known as the Duck-billed Platypus (_Ornithorhynchus paradoxus_ or _O. anatinus_, fig. 125). The head of this animal is furnished with a kind of flat duck’s bill, armed with two horny teeth in the upper jaw, while the body, which is covered with dense fur, resembles that of a beaver. The tail is broad and flat; the legs are short, and the feet are provided with five toes, armed with strong claws and webbed.

This singular animal is found only in Australia and Tasmania. It lives in burrows near watercourses, entered by holes which it digs in the bank, one above the other on the water-level. It spends much of its time in the water, and feeds upon worms and small fishes.

In the males the hind feet are armed with a spur, having an orifice at the extremity. At the will of the animal, there is discharged from this spur a venomous liquid secreted by a gland, which lies along the thigh, and is in communication with the spur by means of a wide subcutaneous duct (Patrick Hill).[164]

It has often been proved in Australia that this liquid, when inoculated by the puncture of the spur, may give rise to œdema and more or less intense general malaise. Interesting details with reference to the effects produced by this secretion have been published by C. J. Martin, in collaboration with Frank Tidswell.[165]

When a dose greater than 2 centigrammes of dry extract of the venom of _Ornithorhynchus_ is injected intravenously into the rabbit, it produces phenomena of intoxication analogous to those observed after inoculation with VIPERINE venoms.[166] Death supervenes in from twenty-five to thirty minutes, and at the autopsy hæmorrhagic patches are found beneath the endocardium of the left ventricle.

This venom has been studied afresh in my laboratory by Noc, thanks to the acquisition of a small supply kindly forwarded to me by C. J. Martin. Noc proved that it possesses _in vitro_ certain properties of snake-venoms; like the venom of _Lachesis lanceolatus_, it induces coagulation in citrate-, oxalate-, chloridate-, and fluorate-plasmas. Heating at 80° C. destroys this coagulant power.

Contrary, however, to what is found in the case of the venoms of _Vipera_ and _Lachesis_, the secretion of _Ornithorhynchus_ is devoid of hæmolytic and proteolytic properties.

Lastly, its toxicity is very slight, at least five thousand times less than that of the venoms of Australian snakes. A mouse is not even killed by 5 centigrammes of dry extract, and in the case of the guinea-pig 10 centigrammes only produce a slight painful œdema.

It has been remarked that the volume and structure of the poison-gland exhibit variations according to the season of the year at which it is observed. It is therefore possible that these variations also affect the toxicity of the secretion (Spicer).[167]

By certain authors the poison of _Ornithorhynchus_ is considered to be a defensive secretion of the males, which becomes especially active in the breeding season, and this hypothesis is plausible. In any case it would seem that as a venom the secretion is but very slightly nocuous.

It will have been seen from the papers quoted above that the chemical nature and physiology of the various venoms, other than those of snakes, are as yet little understood and need further investigation.

The main outlines of this vast subject have scarcely been traced, and the study offers a field of interesting investigations, in which the workers of the future will be able to reap an ample harvest of discoveries, pregnant with results for biological science.