Gram

The gram (alternative British English spelling: gramme;SI unit symbol: g) (Greek/Latin root grámma) is a metric system unit of mass. Gram can be abbreviated as gm or g.

Originally defined as "the absolute weight of a volume of pure water equal to the cube of the hundredth part of a metre, and at the temperature of melting ice" (later 4 °C), a gram is now defined as one one-thousandth of the SI base unit, the kilogram, or 1×10⁻³ kg, which itself is defined as being equal to the mass of a physical prototype preserved by the International Bureau of Weights and Measures.

Official SI symbol

The only unit symbol for gram that is recognised by the International System of Units (SI) is "g" following the numeric value with a space, as in "640 g". The SI does not support the use of abbreviations such as "gr" (which is the symbol for grains), "gm" or "Gm" (the SI symbol for gigametre).

History

The word gramme was adopted by the French National Convention in its 1795 decree revising the metric system as replacing the gravet introduced in 1793. Its definition remained that of the weight (poids) of a cubic centimetre of water. French gramme was taken from the Late Latin term gramma. This word, ultimately from Greek γράμμα "letter" had adopted a specialised meaning in Late Antiquity of "one twenty-fourth part of an ounce" (two oboli), corresponding to about 1.14 (modern) grams. This use of the term is found in the carmen de ponderibus et mensuris ("poem about weights and measures") composed around 400 AD. There is also evidence that the Greek γράμμα was used in the same sense at around the same time, in the 4th century, and survived in this sense into Medieval Greek, while the Latin term did not remain current in Medieval Latin and was recovered in Renaissance scholarship.

Gram-negative bacteria

Gram-negative bacteria are a group of bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation, making positive identification possible. The thin peptidoglycan layer of their cell wall is sandwiched between an inner cytoplasmic cell membrane and a bacterial outer membrane. After staining with crystal violet, an alcohol wash is applied which decolorizes the bacteria showing that their peptidoglycan layer is too thin to retain the stain and enabling identification. A counterstain (safranin or fuchsine) is then added which recolorizes the bacteria red or pink.

Gram-positive bacteria have a thicker peptidoglycan layer in their cell wall outside the cell membrane, which retains the crystal violet stain during the alcohol wash, so long as it is timed correctly. The counter stain may also be absorbed by gram-positive bacteria but the darker crystal violet stain predominates.

Characteristics

Gram-negative bacteria display the following characteristics:

Gram-positive bacteria

Gram-positive bacteria are bacteria that give a positive result in the Gram stain test. Gram-positive bacteria take up the crystal violet stain used in the test, and then appear to be purple-coloured when seen through a microscope. This is because the thick peptidoglycan layer in the bacterial cell wall retains the stain after it is washed away from the rest of the sample, in the decolorization stage of the test.

Gram-negative bacteria cannot retain the violet stain after the decolorization step; alcohol used in this stage degrades the outer membrane of gram-negative cells making the cell wall more porous and incapable of retaining the crystal violet stain. Their peptidoglycan layer is much thinner and sandwiched between an inner cell membrane and a bacterial outer membrane, causing them to take up the counterstain (safranin or fuchsine) and appear red or pink.

Despite their thicker peptidoglycan layer, gram-positive bacteria are more receptive to antibiotics than gram-negative, due to the absence of the outer membrane.

Gram (mythology)

In Norse mythology, Gram, (Old Norse Gramr, meaning Wrath) is the sword that Sigurd used to kill the dragon Fafnir.

Description

Gram was forged by Volund; Sigmund received it in the hall of the Völsung after pulling it out of the tree Barnstokkr where Odin placed it. The sword was destroyed in battle when Sigmund struck the spear of an enemy dressed in a black hooded cloak. Before he died, Sigmund instructed his wife to keep the pieces so that it might be reforged for their unborn son (Sigurd). The sword was eventually reforged by Regin for Sigurd's use. After it was reforged, it could cleave an anvil in half.

In the Nibelungenlied (ca. 13th century), Siegfried says that the name of this sword is Balmung; in Richard Wagner's Ring Cycle (1848–1874), it is called Nothung. The name of the sword seemingly changes depending on the story that you consider.

Gram is also depicted on several of the Sigurd stones.

References

Middle-earth

Middle-earth is the setting of much of J. R. R. Tolkien's legendarium. The term is equivalent to the term Midgard of Norse mythology, describing the human-inhabited world, i.e. the central continent of world of Tolkien's imagined mythological past. Tolkien's most widely read works, The Hobbit and The Lord of the Rings take place entirely in Middle-earth, and Middle-earth has also become a short-hand to refer to the legendarium or its "fictional-universe".

Within his stories, Tolkien translated the name "Middle-earth" as Endor (or sometimes Endórë) and Ennor in the Elvish languages Quenya and Sindarin respectively, sometimes referring only to the continent that the stories take place on, with another southern continent called the Dark Land.

Middle-earth is the central continent of Earth (Arda) in an imaginary period of the Earth's past (Tolkien placed the end of the Third Age at about 6,000 years before his own time), in the sense of a "secondary or sub-creational reality". Its general position is reminiscent of Europe, with the environs of the Shire intended to be reminiscent of England (more specifically, the West Midlands, with Hobbiton set at the same latitude as Oxford).