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. |
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