Among snakes, cobras and coral snakes may be singled out as having a particularly neurotoxic venom; among other animals, the venom of arachnids also falls into the neurotoxic category. The spitting cobra can spray its venom from a distance of about 2.4 (about 8 ft) into the eyes of its victims, causing temporary blindness and great pain. Venom coming in contact with human eyes causes an immediate and severe irritation of the conjunctiva and cornea that, if untreated, may result in permanent blindness. The venom of cobras, a neurotoxin, acts powerfully on the nervous system. With effective serum more available, however, the high death rate from cobra bites in some areas of Asia has decreased. Cobra venom has been used for many years in medical research because it has an enzyme, lecithinase, that dissolves cell walls as well as membranes surrounding viruses.
A common misconception is that baby snake are deadlier than adults. While not proven scientifically, it would seem that an adult cobra can control the the amount of venom delivered, if any, with each bite, depending on the threat it feels. A baby snake has no control over the amount of venom delivered by its bite, thus always giving a full dose. A baby cobra is fully able to defend itself in as little as three hours after entering the world. Cobras are completely immune to the venom produced by their species.
Venom: poison of animal origin, usually restricted to poisons that are administered by biting or stinging and used to capture—and, sometimes, aid in digesting—prey, or for defense. Thus the poisons secreted by the skin of some toads, or accumulated in the bodies of numerous inedible animals, are ordinarily not considered venoms. The most familiar venomous animals are certain snakes and insects and the spiders and other arachnids. Venomous species occur throughout the animal kingdom, however, including the mammals. Some shrews, for example, have venomous saliva, and the platypus bears poison spurs on its hind legs. The severity of a venom's effects depends on several factors, such as its chemical nature, the stinging or biting mechanism involved, the amount of venom delivered, and the size and condition of the victim. For example, all spiders are venomous, but the venoms of most are too weak or minute in quantity to have noticeable effects on humans; in addition, many spiders cannot even puncture human skin. Thus, few of them are poisonous to humans, but their venoms are quite effective on insect prey. Chemically, venoms vary greatly across the animal kingdom and are not readily defined. Snake venoms, for example, are complex mixtures of enzymatic proteins and different toxins. In terms of their effects, however, they may be broadly categorized as hemotoxic (damaging blood vessels and causing hemorrhage) or neurotoxic (paralyzing nerve centers that control respiration and heart action); they may also contain agents that promote or prevent blood clotting. Sometimes a combination of these effects is involved, however, and variations may occur within genera or even within species. The effects of insect stings are usually the result of histamines that produce local irritation and swelling. Serums against various venoms can be produced by injecting animals such as horses with sublethal doses and extracting the immune serum, or antivenin, that the animal body produces. Venoms themselves have occasional medicinal uses; for example, some are used as painkillers in cases of arthritis or cancer, and some serve as coagulants for people with hemophilia.
Note the distinction between venomous and poisonous: venomous refers to a creature that has the ability to secrete or utilize it's venom externally, while poisonous includes creatures that contain a poison substance. Often poisonous creatures are harmless unless eaten. Venomous creatures can often use their poison as a weapon. Cobras are all venomous, yet most are not poisonous, so long as the venom glands are not eaten.