Snake venom is a highly developed form of saliva, injected by the snake into its victim through hollow, modified fangs. Wear and tear are heavy on the fangs, whichare soon blunted or wrenched out in the struggles of prey animals (or when being milked). But fresh fangs are always held in reserve; each poised to move into position when required.
The base of a functioning fang, and often the first reserve fang behind it as well , is penetrated by a duct that leads from a large gland behind the eye. These glands- one on either side of the head - are modified salivary glands surrounded by muscle which, when contracted, forces the clear or yellowish venom along the venom ducts and down through the fangs, squirting out under pressure as if from a pair of hypodermic syringes. Venom may be injectedwith each of a possible series of consecutive bites. Interestingly however, venom is not always injected.
Unerring judgment and great dexterity are needed to obtain snake venoms from such dangerous species as the common tiger snake. Long fangs penetrate a latex membrane stretched over a glass beaker. The beaker collects the venom, which is desiccated undervacuum or freeze-dried.
After drying, the venom crystals are carefully scraped from the beakers for weighing and packaging. Trained staff, whowork with the venom in its various stages of processing, wearprotective masks to avoid poisoning. Apart from the100 tiger snakes, which take turns being'milked' during the Australian Reptile Park's daily public demonstrations, all snake venom extraction is done on a scheduled fortnightly basis.
Australian snake venoms are amongst the most powerful animal toxins known. Dried venom from a single tiger snake milking (top vial), which would be far more than enough to cause a human fatality, is compared with the accumulated venom from approximately 100 tiger snake milkings (right) 300 brown snake milkings (centre), and 100 black snake milkings (left)
An inventory of dried venoms from a wide assortment of native and non-native snake species is maintained at all times. The venom of each species is unique, consisting of a combination of complex proteins, which act on the prey or bite victim in various ways. In most dangerous Australian species, the most significant action of the venom lies in its effect upon the victim's nervous system, hindering the operation of muscles and causing paralysis that can lead to death from heart failure.
Other components present in the venoms of certain species act to destroy blood cells, to cause blood clots or excessive bleeding, or to destroy tissue. Typical early symptoms of bites, where significant envenomation has occurred, include severe headache, nausea, vomiting, confusion, temporary loss of consciousness, fast pulse and tender lymph nodes. Later signs of envenomation may include drooping eyelids, voice change, double vision, difficulty in swallowing and intense abdominal pain, which may be followed by the vomiting of blood.
Antivenoms are produced by the Commonwealth Serum Laboratories in Melbourne. Snake venom is forwarded from the Australian Reptile Park to the laboratories where, after being processed, it is injected into Percheron horses. Over 250 horses take part in the antivenom program, all living the life of luxury. They undergo minimal stress during the inoculation and extraction processes. Inoculation is quite harmless, and extraction is as simple as donating blood for humans.
The horses are given increasing doses of venom over a period of time until they have built up sufficient antibodies to the venom. After this has occurred, antibodies are extracted from the blood, purified and reduced to a useable form.
The antivenoms taken from the horses are used to treat humans suffering from snake envenomation. Injected into the human bloodstream, the antibodies attack the venom, neutralising its effects. The dose of antivenom given to a patient varies according to the species responsible for the bite and, when it can be ascertained, the amount of venom injected. The age and weight of the victim makes no difference to the dose of antivenom required in the treatment.