Archive for the ‘mammals’ 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 Afri­can 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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Stone Swallowing   no comments

Posted at 1:52 pm in Teeth

Those creatures which have no teeth of their own have to resort to dentures. Food eaten by birds is crushed by little stones in their stomachs: the grains are taken into a thick-walled muscular stomach of considerable strength and crushed between the little stones as though between millstones.

Small stones are often to be found in the stomachs of birds. You may find them if you are preparing a chicken for the oven. But this phenomenon is still a puzzle in many respects. What makes birds swallow stones? They do not do it because they are hungry. How do birds know when the stones in their stomachs have worn out and need replacing? What makes them pick up only sufficiently hard stones? As yet, we cannot answer these questions.

Not only birds are fond of swallowing stones. Stones weighing from 350 to 500 grams are often found in the stomachs of whales, walruses and seals. From time to time they belch out these stones and this is why there is often a lot of stones from the sea bottom deposited in places where these pinnipeds spend a good deal of their time when on land. One might think that they decided to establish a geological museum on the sea-shore.

Scientists do not as yet know why sea mammals load their digestive tract with such unusual objects. The reason may be that stones help, as they do in birds' stomachs, to crush such hard parts of their food as mollusk shells and the chitinous shells of arthropods. Another reason may be that stones are used in the struggle with intestinal parasites, which are a particular nuisance to pinnipeds.

Animals are especially apt to swallow stones when they have gone for a long time without food. Hence, the suggestion has been made that swallowing stones prevents the stomach from atrophy (the shrinkage of an organ or tissue with resultant cessation of functioning). Thus, swallow­ing stones keeps the stomach busy when it otherwise has nothing to do.

However, it is quite probable that some sea mammals indulge in stone eating for reasons other than that of digestion. Some scientists believe that stones become indis­pensable when the mammals feed particularly well and get fat. As a result, their mean specific gravity drops and they rind it more and more difficult to submerge in water. Sea­faring animals may also swallow stones as to take aboard some ballast and increase their weight. Calculations prove that the amount of ballast is quite large: some seals had as much as 11 kilograms of stones in their stomachs.

Written by rickweak on January 3rd, 2010

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