Practically all snakes are carnivorous and the prey, which under natural conditions must be captured alive, is swallowed whole, the conical re-curved teeth and the divided lower jaw being adaptations to this method of feeding. The prey may be killed by poison or constriction or swallowed alive ; it is worked round until the head is in the snake's mouth and then commences the laborious swallowing process. The bones supporting the lower jaw are movable on the skull so that the gape of the mouth is tremendous and this, assisted by the stretching of the elastic ligament between the halves of the lower jaw, permits the swal lowing of masses of considerably greater diameter than the snake itself ; the teeth of one side of the mouth are hooked into the victim and then, with this as a fulcrum, the other side is pushed forwards a short distance, the teeth engaged and the same action repeated with the opposite side. The hooked shape of the teeth permits of their being pushed forward but not easily drawn back, and in this way the snake literally draws itself over its food. Teeth are frequently broken off by the victim's struggles, but by the side of each functional tooth is a series of new teeth, in different stages of development, lying within a special fold of the lining of the mouth, the vagina dentis; as soon as a tooth is lost one of the successional series moves into its place and becomes fused to the jaw-bone. Teeth are also the means by which the venom of poisonous species is injected; these "poison fangs" are always situated in the upper jaw either at the front or the hind end and the channel for the venom is either a simple groove or a groove whose edges have met and so produced a tube with openings at the base and the tip of the fang. The venom itself is the product of a modified salivary gland and is a clear straw-coloured liquid containing certain poisonous pro teins, the proportions in which each is present varying according to the type of snake. The two principal constituents are a "haemo lytic" agent which breaks up the blood corpuscles and attacks the lining of the blood vessels and a "neurotoxic" agent which attacks the nerve centres, causing paralysis, and having a special affinity for the nerves supplying the respiratory apparatus; the predominance of one or other of these two bodies determines the nature of the symptoms of snake-bite. If neurotoxic agents pre dominate, paralysis, general prostration and difficulty in breathing are the most dangerous symptoms, but if the patient survives this stage, recovery is rapid and there are few severe local symptoms at the site of the bite ; when, on the other hand, "haemolysins" are the principal constituents of the venom there is no paralysis, though there are severe constitutional symptoms and prostration, but even if this is not fatal, local symptoms follow with local extravasation of blood and much swelling of the bitten parts, which may suppurate and become gangrenous. The venom is destroyed by oxidising agents, such as potassium permanganate, silver nitrate and hypochlorites, and this characteristic is the basis on which first-aid treatment should be given. A ligature should be applied above the fang punctures and then a free incision made into the wounds which should, if possible, be washed out with a solution of bleaching powder or potassium permanganate. The ligature must not be kept on for more than half an hour at a time, being released for a few seconds occa sionally to allow the circulation to return before it is re-applied. Administration of large quantities of stimulants is useless, but small repeated doses may be given if the patient is on the verge of collapse. Despite a large number of so-called "cures" there is only one reliable treatment for snake-bite, and that is by the use of "anti-venines" which are now manufactured in most coun tries where snake-bite is at all common. They are prepared by immunising horses against a particular venom by increasing, regulated doses; the blood serum of the horses is then sterilised and made up into doses ready for inoculation. It has not yet been found possible to prepare a serum which is really efficacious against the venoms of more than one or two snakes, so that, to ensure treatment with the correct anti-venine, an attempt should be made to identify the one responsible for the accident. Above
all, the earlier an anti-venine is administered the better.
No snakes have a larynx or vocal chords and, in consequence, none have a true voice; they are all, however, capable of hissing and some of the larger, heavy-bodied species, with a large lung capacity, can do so loudly enough to be heard at some little dis tance; a few forms have a special piece of cartilage in front of the epiglottis and, when a blast of air is emitted, the vibration of this cartilage produces a sound which has been compared with that of a gently struck tuning fork. Rattlesnakes (q.v.) have a special sound-producing apparatus and some vipers can make a swishing noise by the movement of the scales one over the other.
The majority of snakes lay eggs; these are elongate with a parchment-like shell, and are usually deposited in a situation exposed to moist heat. In some groups, however, they are retained inside the body of the mother until the young are fully developed.
The various families, based largely on characters of the skull, may best be considered separately.
I. Typhlopidae.—Small, harmless, burrowing, worm-like snakes, with the eyes hidden beneath the scales of the head, with a very short, blunt tail, with small, shiny over-lapping scales, no en larged scutes across the belly and with teeth only in the upper jaw; inhabitants of almost all tropical countries. These snakes form burrows in loose soil, and to assist in this operation many have a short spine at the tip of the tail which is dug into the ground to obtain a purchase whilst the rounded head is thrust forward, or retracted, by a looping movement of the body; insect pupae and larvae, ants and earth-worms, seem to form the staple diet. The commonest colouring is brownish or flesh colour, but a few, for instance the common T. punctatus of tropical Africa, are irregularly marked with black and yellow.
3. Ilysidae.—Harmless burrowing snakes, without any distinct neck but with the cylindrical body tapering slightly at either end, with a pair of claw-like vestiges of hind limbs visible on either side of the vent and with slightly enlarged scales on the belly ; teeth are present in both jaws. The few members of this family are larger than most burrowing snakes, attaining a size of 2-1 to 3 ft.; they seldom appear above ground but take readily to water, and their food seems to consist principally of other snakes and eels, all, so far as is known, are ovoviviparous. Ilysia scytale, of tropical South America, coloured a beautiful coral-red with more or less complete black rings, superficially resembles some true coral snakes (Micrurus) ; as the latter are all venomous this is often regarded as an instance of mimicry. Cylindrophis rufus of Burma, the Malayan Region and the East Indies also exhibits what appears to be mimicry, but of a different kind ; the upper surfaces are brown or black, with, as a rule, light cross-bars, the belly is white with transverse black bands, and the tail bright red beneath. When the snake is brought above ground the tail is bent sharply upwards exhibiting the brilliant lower surface and if the animal is touched the tail snaps round in the manner of a striking head. Precisely the same tail colour and actions occur also in another burrowing snake of the same regions, Doliophis intestinalis, but this animal is not only venomous but possesses the largest poison glands of any Elapine snake.