The physiological effects of the various venoms are very different from those that we have just described, when these toxic substances are introduced into the organism otherwise than subcutaneously.
Their direct penetration into the blood-stream, whether by the bite of the snake itself or by experimental intravenous injection, always produces immediate results. With the venoms of Viperidæ, coagulation of the blood and, consequently, death are almost instantaneous. With the venoms of Colubridæ, which, on the contrary, destroy the coagulability of the blood, the toxic effects are less rapid, but after the lapse of only a few minutes asphyxia ensues and the death-struggle is very short.
Absorption by the serous membranes is slower, but is nevertheless effected much more quickly than when it takes place in the subcutaneous cellular tissue. When cobra-venom is injected into the peritoneal cavity of a rabbit or a guinea-pig, the local effects upon the serous membrane are almost nil. No leucocytic exudation is observed; death supervenes before this has had time to take place. The venoms of Viperidæ, on the contrary, produce, directly after their introduction into the peritoneum, an enormous afflux of sanguinolent serosity; the capillary vessels of the serous membrane, immediately becoming distended, allow the blood to filter through their walls, and the animal succumbs after a few minutes, or a few hours, according to the dose injected, with the peritoneum full of blood.
When deposited upon the mucous membranes of the eye, vagina, or urethra, all venoms, those of Colubridæ like those of Viperidæ—but the latter with greater intensity—cause very acute inflammation, comparable to that produced by jequirity; the capillaries become distended, allow leucocytes to exude en masse, and, as for instance upon the eye of the rabbit, a purulent ophthalmia soon establishes itself.
Certain species of Sepedon (Colubridæ), common on the West Coast of Africa, especially in Senegambia and in the hinterland of Dahomey, and to which the name Spitting Snakes has been given, possess the faculty of projecting little drops of venom to a distance by forcibly expelling the air from their lungs, and the natives assert that this venom, when it happens to come into contact with the eyes, causes blindness. This is true to a certain extent, in so far as it produces attacks of purulent ophthalmia which are often serious; but these attacks, like those provoked experimentally in animals, can be cured in a few days when properly treated.
When absorbed by the digestive tract, the venoms of Colubridæ often produce no ill-effects. It is otherwise with those of Viperidæ. The venom of Lachesis, for example, if administered in sufficient doses, sets up acute inflammation of the gastric mucous membrane, and the animals speedily succumb with attacks of gastro-intestinal hæmorrhage, even before it has been possible for the toxic effects upon the nerve-cells to become apparent.
These facts explain the contradictions that are to be found in the works of different investigators upon this subject. It is affirmed by some writers that venom can be swallowed without danger, and they even advise the sucking of venomous wounds in order to hinder its absorption. Others, including Sir Joseph Fayrer, Richards, and Weir Mitchell, have killed pigeons and fowls by making them ingest venom of Vipera russellii, or Crotalus. C. J. Martin, in experimenting upon rats with the venom of Pseudechis (Colubridæ), has succeeded in keeping these animals alive for a whole week by providing them every day with a ration of bread and milk mixed with a dose of venom one hundred times greater than the lethal dose for a subcutaneous injection. This innocuousness of the venoms of Colubridæ, which I have frequently been able to establish by causing them to be ingested by different animals, is explained by the fact that the pancreatic juice and the ptyalin of the saliva very rapidly modify the proteic substances to which these venoms owe their toxicity, so that this disappears. No trace of them is found in the fæces.
The glandular secretions of persons bitten by venomous snakes, and those of animals inoculated with doses of venom calculated to kill only after a few hours, are not infrequently found to be toxic. In the case of the urine in particular this has been shown to be so.
Observations have also been recorded by C. Francis[18] and Sir Joseph Fayrer with reference to the passage of venom through the mammary gland. In the year 1893 a poor Mussulman woman died at Madras from the bite of a Cobra. She was nursing her child at the time, and the latter succumbed in its turn a few hours later, with all the symptoms of poisoning, although it had not itself been bitten, and had been suckled by its mother only once since the bite.
The histological lesions produced by snake poisoning have been particularly well studied by Hindale,[19] Karlinski,[20] Nowak,[21] Louis Vaillant-Hovius,[22] and Zeliony.[23]