Frog

Frogs are a diverse and largely carnivorous group of short-bodied, tailless amphibians composing the order Anura (Ancient Greek an-, without + oura, tail). The oldest fossil "proto-frog" appeared in the early Triassic of Madagascar, but molecular clock dating suggests their origins may extend further back to the Permian, 265 million years ago. Frogs are widely distributed, ranging from the tropics to subarctic regions, but the greatest concentration of species diversity is found in tropical rainforests. There are approximately 4,800 recorded species, accounting for over 85% of extant amphibian species. They are also one of the five most diverse vertebrate orders.

The body plan of an adult frog is generally characterized by a stout body, protruding eyes, cleft tongue, limbs folded underneath, and the absence of a tail in adults. Besides living in fresh water and on dry land, the adults of some species are adapted for living underground or in trees. The skin of the frog is glandular, with secretions ranging from distasteful to toxic. Warty species of frog tend to be called toads but the distinction between frogs and toads is based on informal naming conventions concentrating on the warts rather than taxonomy or evolutionary history; some toads are more closely related to frogs than to other toads. Frogs' skins vary in colour from well-camouflaged dappled brown, grey and green to vivid patterns of bright red or yellow and black to advertise toxicity and warn off predators.

Blister

A blister is a small pocket of fluid within the upper layers of the skin, typically caused by forceful rubbing (friction), burning, freezing, chemical exposure or infection. Most blisters are filled with a clear fluid, either serum or plasma. However, blisters can be filled with blood (known as blood blisters) or with pus (if they become infected).

The word "blister" entered English in the 14th century. It came from the Middle Dutch "bluyster", and was a modification of the Old French "blostre" which meant a leprous nodule—a rise in the skin due to leprosy.

Causes

A blister may form when the skin has been damaged by friction or rubbing, heat, cold or chemical exposure. Fluid collects between the epidermis—the upper layer of the skin—and the layers below. This fluid cushions the tissue underneath, protecting it from further damage and allowing it to heal.

Friction or rubbing

Intense rubbing can cause a blister, as can any friction on the skin if continued long enough. This kind of blister is most common after walking long distances or by wearing old or poorly fitting shoes. Blisters are most common on the hands and feet, as these extremities are susceptible while walking, running, or performing repetitive motions, such as joystick manipulation whilst playing certain video games, playing guitar, etc. Blisters form more easily on moist skin than on dry or soaked skin, and are more common in warm conditions. Less-aggressive rubbing over long periods of time may cause calluses to form rather than a blister. Both blisters and calluses can lead to more serious complications, such as foot ulceration and infection, particularly when sensation or circulation is impaired, as in the case of diabetes, neuropathy or peripheral artery disease (PAD).

Aztec

The Aztec /ˈæztɛk/ people were certain ethnic groups of central Mexico, particularly those groups who spoke the Nahuatl language and who dominated large parts of Mesoamerica from the 14th to 16th centuries. The Nahuatl words aztecatl [asˈtekat͡ɬ] (singular) and aztecah [asˈtekaʔ] (plural) mean "people from Aztlan", a mythological place for the Nahuatl-speaking culture of the time, and later adopted as the word to define the Mexica people. Often the term "Aztec" refers exclusively to the Mexica people of Tenochtitlan (now the location of Mexico City), situated on an island in Lake Texcoco, who referred to themselves as Mēxihcah Tenochcah [meːˈʃiʔkaʔ teˈnot͡ʃkaʔ] or Cōlhuah Mexihcah [ˈkoːlwaʔ meːˈʃiʔkaʔ].

Sometimes the term also includes the inhabitants of Tenochtitlan's two principal allied city-states, the Acolhuas of Texcoco and the Tepanecs of Tlacopan, who together with the Mexica formed the Aztec Triple Alliance which controlled what is often known as the "Aztec Empire". In other contexts, Aztec may refer to all the various city states and their peoples, who shared large parts of their ethnic history and cultural traits with the Mexica, Acolhua and Tepanecs, and who often also used the Nahuatl language as a lingua franca. In this meaning it is possible to talk about an Aztec civilization including all the particular cultural patterns common for most of the peoples inhabiting Central Mexico in the late postclassic period.