multiple sclerosis

Disease of the brain and spinal cord in which gradual, patchy destruction of the myelin sheath of nerve fibres causes interruption or disordered transmission of nerve impulses. Its early symptoms may include limb weakness or trembling, visual problems, sensory disturbances, unsteady walking, and defective bladder control, which come and go irregularly. Attacks grow more severe, and some symptoms become permanent, sometimes with eventual complete paralysis. Average survival from onset is about 25 years, but a rare acute form progresses over months. The cause remains uncertain and treatment unsatisfactory. Corticosteroids may ease symptoms. MS may be due to a delayed immune response that attacks the myelin sheaths; suggested causes include various common viruses. Dietary causes have also been suggested.

Learn more about multiple sclerosis with a free trial on Britannica.com.

formerly multiple personality disorder

Rare condition indicated by the absence of a clear and comprehensive identity. In most cases two or more independent and distinct personality systems develop in the same individual. Each personality may alternately inhabit the person's conscious awareness to the exclusion of the others, but one is usually dominant. The various personalities typically differ from one another in outlook, temperament, and body language and might assume different first names. The condition is generally viewed as resulting from dissociative mental processes—that is, the splitting off from conscious awareness and control of thoughts, feelings, memories, and other mental components in response to situations that are painful, disturbing, or somehow unacceptable to the person experiencing them. Treatment is aimed at integrating the disparate personalities back into a single and unified personality.

Learn more about dissociative identity disorder with a free trial on Britannica.com.

A malignant proliferation of abnormal plasma cells that populate the marrow-containing bones of the body. The affected plasma cells produce myeloma protein, a monoclonal antibody that replaces normal antibodies in the blood, thereby increasing susceptibility to infection and renal failure. Symptoms include pain, anemia, weakness, infection, a tendency to hemorrhage, shortness of breath, kidney insufficiency, bone fractures, and neurological symptoms. It is considered a progressive and incurable disease; treatments with thalidomide, bone-marrow transplantation, and high-dose chemotherapy may extend life span, although success rates are variable.

Learn more about multiple myeloma with a free trial on Britannica.com.

Birth of more than one child from one pregnancy. Twins are most common, born in 1 of about every 80 pregnancies. Identical twins develop from a single fertilized egg, which splits into two genetically identical embryos (though physical traits may be modified during their development); they occur randomly but are more likely in older mothers. Incomplete or late division results in conjoined twins. Fraternal twins develop from two eggs fertilized by two sperm and are no more genetically alike than are other siblings. Most common among persons of African ancestry and least common among those of Asian ancestry, fraternal twins seem to run in families. Repeated twinning produces triplets, quadruplets, and so on; these multiples may be identical, fraternal, or a combination. The use of fertility drugs has increased the number of high-order multiple births. Medical and psychological “twin studies” compare fraternal and identical twins to learn about genetic influences on various characteristics and diseases.

Learn more about multiple birth with a free trial on Britannica.com.

Multiple-image Network Graphics (MNG, ) is a public graphics file format for animated images.

MNG is closely related to the PNG image format. When PNG development started in early 1995, developers decided not to incorporate support for animation, not least because this feature of GIF was seldom used at the time. However, work soon started on MNG as an animation-supporting version of PNG. Version 1.0 of the MNG specification was released on January 31 2001.

Software that supports MNG

MNG is currently not as widely supported as PNG. Nonetheless, Konqueror has native MNG support, and MNG plugins are available for most other web browsers. Mozilla browsers and Netscape 6.0, 6.01 and 7.0 included native support for MNG until the code was removed in 2003 due to code size and little actual usage, causing complaints on the Mozilla development site. As a result, a MNGzilla project was started to offer patched Mozilla and Firefox browsers. Neither Internet Explorer nor Safari currently support MNG. Recent Sony Ericsson phones support MNG files in their themes.

The MNG developers hope that in time MNG will begin to replace GIF for animated images on the World Wide Web, just as PNG has already begun to do for still images. However, with the expiry on LZW patents and existence of alternative file formats such as Flash and SVG, combined with lack of MNG supporting viewers, web usages were far less than expected.

Technical details

The structure of MNG files is essentially the same as that of PNG files, differing only in the slightly different signature (8A 4D 4E 47 0D 0A 1A 0A in hexadecimal) and the use of a much greater variety of chunks to support all the animation features that it provides. Images to be used in the animation are stored in the MNG file as encapsulated PNG or JNG images.

Two versions of MNG of reduced complexity are also defined: MNG-LC (low complexity) and MNG-VLC (very low complexity). These allow applications to include some level of MNG support without having to implement the entire MNG specification, just as the SVG standard offers the "SVG Basic" and "SVG Tiny" subsets.

MNG does not yet have a registered MIME media type, but video/x-mng or image/x-mng can be used. MNG animations may be included in HTML pages using the