Certain Gastropodous Molluscs, chiefly Murex brandaris and M. trunculus, possess purple glands from which it is possible to extract a very active venom (Raphaël Dubois)[136] by crushing them up with sand and alcohol. The alcoholic liquid, filtered and evaporated in a water-bath, yields a brown oily fluid. The subcutaneous injection of a few drops of this into a frog is sufficient to produce very decided toxic effects. Sluggishness and slowness of movement are seen to supervene fairly quickly; reflex actions are still exhibited, but the animal is no longer able to jump.
If the dose be not too strong, this condition of paresis lasts for several hours, and then disappears. In most cases, however, the paresis is succeeded by complete paralysis, and the animal appears as though suffering from curare. Yet the fact is that the venom is neither curare-like nor cardiac; the heart, muscles, motor endplates, and motor and sensory nerves are spared; the nervous centres alone are attacked, especially the encephalon. The animal dies without convulsions.
Sea and fresh-water fishes (golden carp) are very sensitive to this venom; warm-blooded animals are refractory. It is therefore probable that, in the species of Murex, the purple gland is a poison-gland serving for defence, or for the capture of the prey upon which these molluscs feed.
Among the Cephalopods, the Octopods (Octopus vulgaris, common octopus, Eledone moschata, musky octopus, of the Mediterranean) possess two pairs of salivary glands, a small anterior pair, and a posterior pair of considerable size.
The Decapods (cuttle-fishes [Sepia], &c.), have only posterior salivary glands, of smaller dimensions in proportion to the size of the body.
On being crushed and macerated in water, the anterior glands yield a limpid and slightly acid juice; the posterior glands produce a viscid, ropy fluid, filterable with difficulty and neutral. The latter has an immediate paralysing effect upon Crustacea. It contains a substance of a diastasic nature, precipitable by alcohol, and destructible by heating for an hour at 58° C.
Owing to the poisonous properties of this juice, Octopods succeed in overpowering large prey, such as lobsters and crabs. Once they are seized by the tentacles of the octopus, or cuttle-fish, a bite inoculates these animals with venom that immediately destroys their power of movement, and the Cephalopod is able to continue its meal in perfect security, without having to fear the pincers of its prey.
An experimental study of this venom has been made by A. Briot,[137] who found that crabs are very sensitive to it, while rats, frogs, rabbits, and fish do not appear to experience any inconvenience.