The reserve or successional teeth, which are always present just behind or on the side of the functional fang of all venomous snakes, are in no way connected with the duct until called upon to replace a fang that has been lost. It could not be otherwise, since the duct would require a new terminal portion for each new fang; and as the replacement takes place alternately from two parallel series, the new venom-conveying tooth does not occupy exactly the same position as its predecessor.
Two genera, Doliophis among the elapids and Causus among the viperids, are highly remarkable for having the venom gland and its duct of a great length, extending along each side of the body and terminating in front of the heart. Instead of the muscles of the temporal region serving to press out the venom into the duct, this action is performed by those of the side of the body.
When biting, a viperid snake merely strikes, discharging the venom the moment the fangs penetrate the skin, and then immediately lets it go. A proteroglyph or opisthoglyph, on the contrary, closes its jaws like a dog on the part bitten, often holding on firmly for a considerable time. The venom, which is mostly a clear, limpid fluid of a pale straw or amber colour, or rarely greenish, sometimes with a certain amount of suspended matter, is exhausted after several bites, and the glands have to recuperate.

Mechanics of spitting

Venom can be ejected otherwise than by a bite, as in the so-called spitting cobras of the genera Naja and Hemachatus. Some of these deadly snakes, when irritated, are capable of shooting venom from the mouth, at a distance of 4 to 8 feet. These snakes' fangs have been modified for the purposes of spitting: inside the fangs of a spitting cobra is a channel which makes a ninety degree bend to the lower front of the fang. When the snake is threatened the muscles of the venom gland squeeze the venom sack and as a result venom is projected forward. Spitters may spit thirty or forty times in succession, and even then the snake is still able to deliver a fatal bite.
Spitting is a defensive reaction only. The snake tends to aim for the eyes of a perceived threat; a direct hit can cause temporary shock and blindness through severe inflammation of the cornea and conjunctiva. While there are no serious results if the venom is washed away at once with plenty of water, the blindness caused by a successful spit can become permanent if left untreated. Contact with the skin is not in itself dangerous, but open wounds may become envenomed.


Some Effects
There are three distinct types of venom that act on the body differently.

• Hemotoxic venoms act on the heart and cardiovascular system.
• Neurotoxic venom acts on the nervous system and brain.
• Cytotoxic venom has a localized action at the site of the bite.

It is noteworthy that the size of the venom fangs is in no relation to the virulence of the venom.
But how dangerous really are venomous snakes?

Amongst venomous Colubrids, only one African species, the boomslang (Dispholidus) has fangs big enough and a potent venom to harm a human being, even if it is a non aggressive species difficult to provoke. The rear fanged snakes have to chew their prey while swallowing it in order to administrate the paralyzing venom which initiates the digestion and they usually eat small prey, like lizards, frogs. Moreover, their venom in most cases is weak.

Cobra type venomous snake tends to bite and keep a hold on, as many have shorter fangs and some coral snakes even chew. But vipers, with their highly efficient injecting mechanism, effectuate the bite sometimes in 1/40 of a second and then retreat.

The snake venom varies a lot between different groups. Some venoms are neurotoxic and paralyze the muscles. The victim dies of suffocation and heart attack. All cobra-related snakes have extremely potent neurotoxic venom, but also some rattlesnakes, moccasins and pitless vipers.

Some venoms, like cobra's, produce anaphylactic shock. Other venoms action like a powerful digesting juice, producing necrosis and hemorrhage. Most vipers possess a powerful venom of this type and with their huge fangs can introduce large amounts of venom into the wounds.

The bushmaster (Lachesis muta) , a pit viper from tropical America produces general necrosis, generalized internal hemorrhage and external hemorrhage through all the orifices.

Sea snake venom provokes elimination of mioglobin (muscle protein) through the kidney and necrosis into the muscles, but these snakes are not known to have ever bitten a person.

Some animals are very sensitive to snake venom, like birds, others not, like mongooses that consume venomous snakes and some species, like snake eating snakes (king cobra, king snakes), are totally immune to snake venom. Many snakes have venom specialized for their prey, like an aquatic Colubrid, Fordonia, whose venom is toxic only for the crabs. Ultimately, the aggressiveness is important on appreciating the danger posed by a snake species, and most Elapids and Viperids are both aggressive and highly toxic.