Sir Joseph Fayrer.—"The Tanatophidia of India." Also, "Researches in conjunction with Richards, Brunton and Eward."
Wall.—"On the Difference in the Physiological Effects produced by the Poison of Indian Venomous Snakes." Proc. Royal Soc., 1881, vol. xxxii., p. 333.
Among those enumerated above Wall is the only one who formulated a correct and thoroughly scientific theory of the action of snake-poison, which has since been confirmed by Australian research and by Feoktistow's elaborate experiments. It is strange that, after finding the theory that explained all the phenomena, he did not follow it up by applying the antidote to which his theory should have led him.
SNAKE-POISON AND ITS ACTION.
The poison gland of snakes is the analogue of the parotid gland of mammals, both in position and structure. Its acini or alveoli are lined with a layer of secretory, columnar, finely granular cells and arranged with great regularity along the excretory duct, which is straight and cylindrical and opens with vipers into the hollow poison fang, with our colubrines into the groove on the anterior surface of it. Snake-poison, as it leaves this gland, is a thin, albuminoid, yellow liquid of neutral reaction. On exposure to the air it becomes viscid and slightly acid. Of its chemical composition we know as yet but little, and it is very questionable whether the most perfect chemical analysis of its constituents would ever have given us a clue to its action or will enrich our present knowledge of it. Like all albuminoid secreta it becomes putrid after prolonged exposure and then, through ammonia production, loses its acid, and assumes an alkaline reaction, still, however, though in a modified degree, retaining its toxic properties, which are completely lost only after an exposure of many months. Feoktistow found that freezing at 1° R. caused the poison to separate into a solid mass and a thin, very yellow liquid, which, even at a temperature of 4° R., remained liquid, and the poisonous properties of which greatly exceeded those of the solid mass. Boiling diminishes and, continued for any length of time, completely destroys the potency of the poison.
The microscope has done good service in the investigation of snake-poison. It has, in the first place, informed us with absolute certainty that there are no micro-organisms or germs of any kind in the fresh poison immediately after it leaves the gland. But a still more important revelation we owe to it is the fact that these organisms, when we introduce them into a 2% solution of the poison, do not die, but live, multiply, and enjoy their existence most lustily, as they do in any other non-poisonous albuminoid liquid, whilst animals of a higher type—say a snail or a frog—soon perish in it. In watching the movements of the latter we find that they get slower and slower, and finally cease. We now follow up the interesting research, and take two frogs. Under the skin of one of them we inject a few drops of the poison solution, the other one for comparison we leave intact, and place both into a glass globe partly filled with water. In a very short time we have no difficulty to identify the poisoned frog. Its hind legs begin to drop and their movements become sluggish. This difficulty increases from minute to minute, until at last all motion ceases, and the legs hang down completely paralysed. At the same time we observe that the animal shows increasing difficulty of breathing, that, even when taken out of the water, and placed on the table before us it gasps for breath and is unable to move. At last respiration ceases altogether and the frog dies.
Two problems now present themselves for solution. In the first place we have to account for the fact of the snake-poison leaving the lower forms of animal life intact and being fatal to the higher ones. The symptoms we have observed in the frog point unmistakably to an affection of the nervous system as their cause. Now we know that the lower forms which the poison does not affect have no such system, and we are justified to infer that to the absence of this system they owe their immunity. This inference leads us on to a second one equally justifiable, namely, that there is a certain unaccountable attraction between the delicate nerve tissue and the subtle ophidian poison, which renders the latter a specific nerve poison.
Our second problem is to ascertain the nature of the change in the nerves, to find out, if possible, whether it is merely functional or an actual interference with the structure of either cells or fibres. With this end in view we once more consult the microscope. We make two preparations, one of nerve fibres and of nerve cells of the poisoned frog, and, under the microscope, compare them carefully with an analogous one from the killed healthy frog. The result is purely negative as regards structural change. Both present identical and perfectly normal pictures of apparently healthy cells and fibres. There being no visible structural change we are driven to the conclusion that only a functional one has been effected by the poison, and with the symptoms observed all pointing in that direction, that it is of central origin.