Category Plants & Animals

           Have you ever seen a cat sitting in the dark? Though its body is not visible, yet its yellow eyes shine in the darkness. The eyes of tiger, leopard, lion etc. also shine in the darkness or night just like the eyes of a cat. Besides these, there are many other animals whose eyes shine in the dark.

           The eyes of these animals have a thin layer of a special crystalline substance which reflects the light falling on it. This reflected light is the cause of the shine. In the night, even the smallest amount of light falling on this crystalline surface gets reflected and thus we see the shining eyes. Animals with such eyes that can see things clearly in darkness are called nocturnal animals.

           Studies made on cats have shown that behind the retina of eyes, there is a crystalline layer called the ‘luminous tapetum’, which reflects light. Due to this layer the cat can see clearly in dim light and its eyes shine in the dark when the light is directed on them. Many animals do not have this crystalline layer; hence their eyes do not shine in the dark.

          It has been observed that the colour of the shine is different in different animals. It depends upon the number of blood vessels present in their eyes. If the number of blood vessels is large, the colour of the shine is red and if the number of blood vessels is small the colour of the shine is white or pale yellow.

Dog is regarded as a faithful animal. But when it goes mad it becomes very dangerous. If a mad dog bites someone, it leads to his death if not treated properly.

              A dog goes mad when it suffers from a disease called ‘rabies’. This disease is caused by a virus which is carried by air or by some wild animals and enters the dog’s body through a wound in its skin. The virus is bullet shaped having a diameter of about 70 milli-microns and a length of about 210 milli-microns. It moves from the saliva to the infected wounds and through sensory nerves to the central nervous system, multiplies there and then destroys brain cells. The dog becomes lazy, suffers from fever and loses all interest in food. In about 4-6 weeks, when these viruses affect the dog’s brain, the dog gets excited. It growls and barks and saliva froths from the mouth. During this period, the dog can bite anybody. This is the stage when the dog is said to be mad. After these symptoms appear, it is likely to die within 3 to 5 days. Some infected dogs do not go mad but show signs of paralysis, called ‘dumb rabies’.

             When a mad dog bites a man, the virus present in its saliva enters man’s body through the wound. Initially the victim experiences mental weakness and uneasiness which is followed by fever. He suffers from lack of sleep and feels frightened. The muscles in his throat get slackened and he faces difficulties in swallowing food or liquid. He is afraid of water. That is why this condition is also called ‘hydrophobia’ which means ‘fear of water’. These signs appear in the victim within one to three months after dog’s bite. In cases of dog-bite, the affected portions should be immediately cleaned and anti-rabies injections should be given to the victim within three days of the bite, the number of injections varying from 3 to 14 depending on the location and number of bites.

             The virus of rabies also attacks foxes, jackals, monkeys, cats and rats because they have the least contact with us. 

            Ants are insects that belong to the order Hymenoptera. More than two thousand species of ants have been studied by scientists. Ants are found in most parts of the world. Most ants are smaller than an inch.

            Ants are social animals and have their own kingdoms. This means that they live together in large colonies or groups. Some colonies may contain millions of ants. Most colonies make nests in the ground or in dead trees.

            There are three kinds of ants in each colony – queens, laying eggs; males who do not work; and a corps of female workers. An ant colony contains too many cells or chambers for different purposes. The queen lives in one, laying eggs. Next door is the hatching room, from which the grubs as they turn into pupae are carried into another room to develop. The other rooms are used for special purposes such as storing food etc. An ant colony may contain several queens each with its own suite of rooms. Worker ants collect food, feed the young ants and build the nest. Some species of ants also have female soldier ants. They protect the nest. 

Continue reading “Do Ants also have their kingdoms?”

           An owl is a bird of prey with large head and eyes, short neck, broad wings and sharp claws. About 130 species of owls are found around the world. In some countries, they are treated as in auspicious birds, while in others; they are regarded as symbol of wealth and wisdom. What is peculiar about owl is that they can see more clearly at night than during the day. In fact they “come to life” at night and are an apt example of ‘nocturnal’ birds. Birds which can see more clearly at night rather than during the day are known as nocturnal birds. On the other hand, birds which have a clearer vision along the day time than during night are called ‘diurnal’.

             You must be very curious as to how nocturnal birds in general and owls in particular can see so clearly at night.

             To understand this, it is essential to know how we see things. Light scattered by an object is focused on to the screen of the eyes by the lenses inside the eyes. This screen of the eyes is called the retina. An inverted image of the object is formed on the retina which is carried to the brain by optic nerves. This is erected by the brain and thus we see the object.

                 The owl’s eyes have four special features due to which it can see more clearly at night. Firstly, the distance between the lens of its eye and the retina is more than the distance in the case of human eyes. Due to this, the image formed on the retina is bigger in size. Secondly, the number of ‘rods’ and ‘cones’ (special cells which help in the vision) in the retina is very large – almost 10,000 per sq mm compared to 2,000 per sq mm in our eyes. Thus, the owl can see five times more than us. Thirdly, its eyes have a red coloured material, chemically a protein, which makes its eyes more sensitive to light. Fourthly, the pupils of its eyes can dilate more, thus allowing even the smallest amount of light to enter into the eyes. Because of these four factors, the owl can see more clearly in darkness. Due to the extreme sensitivity of their eyes to light, objects appear too bright and uncomfortable to the eyes in the bright light of the day. Surprisingly enough, an owl can rotate its head by 180° i.e. it can see at the back of his head.