Its physiological effects are especially intense in the case of the arthropods upon which the scorpion habitually feeds, and in that of vertebrates in general. Batrachians, fishes, birds, and mammals are extremely susceptible to this poison. Half a milligramme of dry extract injected subcutaneously is sufficient to kill a guinea-pig, and 1 milligramme is lethal to the rabbit.
In poisoned animals there is first observed a period of violent excitement, accompanied by very acute pains; these are followed by muscular contractions, and finally by paralysis of the respiratory muscles, as in the case of intoxication by cobra-venom.
The effects of scorpion-poison, which clearly indicate the presence of a neurotoxin, have been very well described by Valentin,[116] Paul Bert[117] and Joyeux-Laffuie. Kyes[118] has prepared a lecithide from scorpion-venom, which hæmolyses red corpuscles as do the lecithides of cobra-venom, and I myself[119] have established the fact that the antivenomous serum of a horse vaccinated against cobra-venom effectively protects mice and guinea-pigs against intoxication by the venom of Scorpio occitanus; this has been verified by Metchnikoff. There is, therefore, a close affinity between this venom and that of Colubrine snakes.
On the other hand, it has been shown by the investigations of C. Nicolle and G. Catouillard that the same antivenomous serum has no effect upon the much weaker venom of the scorpion of Tunis (Heterometrus maurus), which, in the case of man and mammals in general, scarcely does more than produce a transient œdema at the point of inoculation.
The venom of Heterometrus maurus is, however, toxic enough to the sparrow. When one of these little birds is inoculated in the pectoral muscles with the contents of the poison-glands of a single scorpion belonging to this species, the following symptoms are observed: Immediate rigidity, doubtless connected with the pain, then, after a few seconds, depression and relaxation of the muscles. The bird remains upright, but its body sinks down more and more until it comes into contact with the ground; if on a perch, it soon becomes unsteady and drops off. There is dyspnœa, which any effort increases, and death supervenes suddenly; all at once the sparrow falls on its side, stiffens, sometimes has a few convulsions, and then finally becomes still. The time occupied by these phenomena is always short, although it varies from two minutes to half an hour.
Scorpion-venom is a strong irritant to the mucous membranes. When dropped into the eye of a rabbit it produces acute ophthalmia.
It has often been asserted that scorpions kill themselves with their own venom if enclosed in a circle of fire. This is an absolute myth, for it is easy to prove by experiment, as was done by Bourne at Madras,[120] that these animals cannot be intoxicated by their own poisonous secretion, nor by that of other individuals of the same species. Moreover, it has been established by Metchnikoff,[121] in very definite fashion, that the blood of the scorpion is antitoxic. If 0·1 c.c. of this blood be added to a dose of venom lethal to mice in half an hour, a mouse injected with this mixture resists indefinitely. This antitoxic power is exhibited both by Scorpio afer and the Algerian Androctonus.
(c) Myriopods.
It has been shown by Phisalix and Bertrand that certain species of Myriopods, including those of the genus Julus (Order Chilognatha, e.g., Julus terrestris), secrete throughout the entire extent of their body a volatile venom, which these authors compared to quinone.
The species of the genus Scolopendra (Order Chilopoda; Scolopendra cingulata, found in the South of France, Spain and Italy; S. gigantea and other forms, common in Africa, India, Indo-China and Equatorial America), have the second pair of post maxillary appendages transformed into formidable poison-claws, with which they can inflict bites which are very painful to human beings.