Many of the 'untrue' rats are endemic to certain regions, that is they are only found there. Very often, they live on islands. In many cases, these species are also endangered of disappearing. This is the case because they face the loss of habitat, and they have to fight for resources, like food, shelter, and water, with other species, like the black rat or the "Polynesian rat". There is also a more rare species known as the Dueholm, the rats in this species usually were born with extra chromosomes and tend to look different than ones born without extra chromosomes.
People keep some types of rats as pets called "fancy rats". Fancy rats are domesticated brown rats. People have kept rats as pets since the 19th century. Rats are social and smart animals that can be trained. They also like to play with toys. Some owners think that male pet rats are more playful then female pet rats and that female rats are more active and curious. Pet rats do not act the same as wild rats. They do not have more diseases than other common pets.
Pet rats live 1 to 3 years. Female rats are smaller than male rats. Pet rats have been known to "laugh" when tickled. They can be all one color or have spots or other coloring. Some rats have no hair. These are called hairless rats.
Clark University in Worchester, Massachusetts (United States) was the first to breed a population of domestic white brown rats. They did this to study the effects of diets, amongst other things.
Since then, rats have been used in many experiments. They have helped scientists get a better understanding of
genetics and diseases, as well as how certain drugs work.
Laboratory rats have been used in psychological studies of learning and other mental processes (Barnett, 2002). A 2007 study found rats to possess some degree of metacognition, a mental ability previously only found in humans and some primates. In general, it has been difficult to measure intelligence in rats. Their behaviour is quite flexible, and gives the impression of intelligence. Flexible behaviour is good for problem-solving and learning.
Domestic rats are very different from wild rats. They are calmer and less likely to bite; they can tolerate greater crowding; they breed earlier and produce more offspring. Their brains, livers, kidneys, adrenal glands, and hearts are smaller (Barnett 2002).
Brown rats are often used as model organisms. Genetic research is usually done with mice. Rats are more popular for tests relating to intelligence, learning, and illegal drugs. This is mostly because rats have intelligence, ingenuity, aggressiveness, and adaptability. Their psychology seems to be very similar to human psychology. Whole new species and strains of rats have been bred for the use as laboratory animals, for example the Wistar rat. Much of the genome of "Rattus norvegicus" has been sequenced.
Rats are opportunists. If they have the choice between a food that will need a fight to get, and another food that will not, they take the food that does not need a fight. For this reason, rats have lived close to humans for a long time. Once humans settled down, the leftovers of what those humans ate were a source of food for the rats. So the rats followed.
Rats are present in almost all settlements. In cities, they often live in the sewers.
Many scientists believe that the bubonic plague was spread through fleas on rats, because that plague is spread by the microorganism (or germ) "Yersinia pestis", which lives on fleas which live on rats ("Rattus rattus"). Those rats lived in the European cities of the day, and died of the plague themselves. Some scientists believe that the plague spread faster than the rats. If this is true, the rats cannot be the main carrier. More research is needed to find out if this is true. People believe this disease was the 'Black Death'. It killed nearly a third of the population of Europe, in many epidemics in the Middle Ages.
Rats can carry diseases. Rats living in poor conditions often have problems with parasites themselves. Not many diseases carried by rats can spread to humans. One of those is called Leptospirosis, another one is the plague.
Branch
A branch is the part of a tree that grows out from the trunk of a tree.
Spoon
A spoon is a tool for eating. It is usually used for eating foods that are like liquids (like soup and yogurt), and it can also be used for stirring. Humans use spoons every day. Some solids (like cereal and ice cream) are also usually eaten with spoons. A ladle is a bigger type of serving spoon used for soup, stew, or other foods.
There are many different types of spoons. There are dessert spoons, soup spoons, baby spoons, teaspoons, tablespoons and others. There are also spoons that are collector items and are worth a lot of money. Some musicians even use two spoons as a musical instrument like a castanet.
Spoons have been used as tools for eating since Paleolithic times. Prehistoric peoples probably used shells, or small pieces of wood as spoons. Both the Greek and Latin words for spoon come from the word "cochlea", which is a spiral-shaped snail shell. The Anglo-Saxon word "spoon", means a chip or splinter of wood.
Cutlery
Cutlery refers to tools used for preparing, serving and eating food. The most common types of cutlery are knives, spoons and forks. Other words for cutlery are silverware, tableware, utensils and flatware.
The best quality cutlery may be made of silver, but more often silver plating. Stainless steel is used for most good quality household cutlery. Pewter was often used in the past for cheap cutlery. Nickel silver, sometimes called German silver, is another alloy, with copper, nickel, and zinc in it. Plastic cutlery is used for eating fast food, because it is very cheap, and may be thrown away afterwards.
Serving practice and use of cutlery varies somewhat between cultures. Formal dinners have cutlery set out in a traditional manner. There will be two sets of knives and forks, an outer smaller set for the first course and a larger inner set for the main course. Cutlery for later courses will usually be delivered with those courses. In an informal restaurant, cutlery may come wrapped in a cloth napkin (serviette).
Chinese and Japanese food is eaten with chopsticks, and food pre-cut to a size suitable for that method. Some other oriental cuisines are eaten by fork and spoon, with no knife.
Vase
A vase is a container, often used for flowers. They can be made from a number of materials, including glass and ceramics. Many vases are decorated or painted but some are left plain. It sometimes is used for decorations in American and Chinese homes. It can be a big part of culture in many countries.
Yemen
The Republic of Yemen or Yemen is a nation in the Middle East. It is the old North Yemen and South Yemen, in the south of the Arabian Peninsula. It borders Saudi Arabia and Oman on the north and the east. To the south is the Guardafui Channel and Gulf of Aden, and to the west is the Red Sea. Yemen owns the island of Socotra (217 miles) to the south off the coast of East Africa. A person or thing from Yemen is called "Yemeni". Yemen's capital city is Sana'a.
Yemen is the origin land of all Arabs in the Middle East. In ancient times, Yemen was an important center of trade and power. Many powerful kingdoms were in Yemen, including the Sabaeans. Yemen was important in the trade of spices as well. It was known to the ancient Romans as "Arabia Felix" ("Happy Arabia" in Latin). They called it Happy Arabia because the area was so beautiful and powerful.