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]
Fig. 125.—Ornithorhynchus paradoxus. (After Claus.)
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.