Archive for the ‘saliva’ tag

Teeth and Venom   no comments

Posted at 5:23 pm in Teeth

Usually, if nature undertakes experiments with poisons, it does not stop half-way, but creates something capable of inspiring real horror, as, for example, poisonous snakes whose bite may be fatal for man.

Now, from where does snake venom come? The venom is merely the snake's saliva secreted by somewhat modified salivary glands opening into a groove inside the tooth. The venom is only secreted when the snake bites, pressing against a little sac at the base of the tooth. During the bite all the venom is injected into the wound.

Some snakes proved very ingenious in developing their lethal weapon. Cobras (the rose and zebra type) and other AfriĀ­can snakes perfected their technique of biting and are very good at spitting their venom. Their poisonous fangs differ somewhat from those of their fellow snakes. The groove along which the venom is ejected does not open out at the very tip of the tooth but some distance away from it (evidently to facilitate ejection), widening into a sort of funnel. For this reason, if the bite is not deep, the poison may not reach the wound, but disperses in fine drops over a wide area. As in a shot-gun the strike area is the larger, the greater the distance between the snake and the target.

Snakes are experts at spitting venom and have a range of up to four metres. This range is achieved by combining the pressure in the venom sac with the inertia of movement, achieved by jerking the head forward with the simultaneous ejection of the venom. If the venom gets into the eyes, the mucous membrane of the nose or the mouth of small mammals, they will die. Such a long-range weapon is more efficient than in other poisonous snakes.

Not only snakes have poisonous saliva. In the Pacific, near the Island of Fiji, New Guinea and Samoa there live gastropod (univalve) mollusks with beautiful, cone-like shells as long as 15 centimetres in length. However, one should not touch these cones. The crafty mollusk is sure to bite you with the sharp teeth of its radula. The poison of these creatures, especially that of the larger ones, is fatal to man.

Written by rickweak on January 6th, 2010

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Importance of Saliva   no comments

Posted at 5:12 pm in Teeth

In far from all cases are the teeth the best possible tools, and nature has not hesitated to substitute more perfect technical means for them. Many species of the prosobranchiate snails feed on mollusks which are rather large and enclosed in a hard shell. To make a hole in the shell with a radula would take weeks or even months, and the radula would wear out. Therefore, these snails use a specific saliva instead of teeth, which is a four-percent solution of sulphuric acid. Nor is this very strange, for if the glandular cells of man's stomach secrete hydrochloric acid, why should snails not make use of sulphuric acid?

The acid secreted by the snails is so strong that it hisses and effervesces when falling on marble. It dissolves the mollusk shells quite easily. When attacking their prey, the snails apply their saliva to the shell which loosens a small section of it. The preying snail then bores a hole with its radula, inserts its proboscis and is then able to enjoy eating the defenceless victim.

It is not always enough to crush food for it to pass easily into the gullet. This is why the 'preparatory shop' contains the large and small salivary glands for both the mechanical and chemical processing of food. Saliva performs many important functions, but the most important seems to be to wet each lump of food which otherwise would not pass into the oesophagus. Anyone who had a chance to observe the European pond tortoises was easily convinced of the importance of saliva. The pond tortoises have no salivary glands. They eat their prey in water, amply washing down each mouthful. But on land they are helpless since completely dry food sticks in their throats.

The saliva of most animals contains substances (enzymes) which are the first to act chemically on the food being taken in. Nature subsequently developed these properties, making saliva somewhat poisonous. This is necessary as numerous microorganisms, most of them harmful to the organism, may lodge in the moist membrane of the mouth and the remains of food stuck between the teeth.

Written by rickweak on January 4th, 2010

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