of oxygen. this could be a place where the body is buried in organic material and oxygen can not reach it. this process of putrefaction has a bad odor accompanied by it due to the hydrogen sulfide and organic matter containing sulfur. artificial preservation embalming is the practice of delaying the decomposition of human and animal remains. embalming slows decomposition somewhat but does not forestall it indefinitely. embalmers typically pay great attention to parts of the body seen by mourners, such as the face and hands. the chemicals used in embalming repel most insects and slow down bacterial putrefaction by either killing existing bacteria in or on the body themselves or by "fixing" cellular proteins, which means that they cannot act as a nutrient source for subsequent bacterial infections. in sufficiently dry environments, an embalmed body may end up mummified and it is not uncommon for bodies to remain preserved to a viewable extent after decades. notable viewable embalmed bodies include those of: eva perón of argentina, whose body was injected with paraffin was kept perfectly preserved for many years, and still is as far as is known (her body is no longer on public display). vladimir lenin of the soviet union, whose body was kept submerged in a special tank of fluid for decades and is on public display in lenin's mausoleum. other communist leaders with pronounced cults of personality such as mao zedong, kim il sung, ho chi minh, kim jong il and most recently hugo chávez have also had their cadavers preserved in the fashion of lenin's preservation and are now displayed in their respective mausoleums. pope john xxiii, whose preserved body can be viewed in st. peter's basilica. padre pio, whose body was injected with formalin before burial in a dry vault from which he was later removed and placed on public display at the san giovanni rotondo. environmental preservation a body buried in a sufficiently dry environment may be well preserved for decades. this was observed in the case for murdered civil rights activist medgar evers, who was found to be almost perfectly preserved over 30 years after his death, permitting an accurate autopsy when the case of his murder was re-opened in the 1990s. bodies submerged in a peat bog may become naturally "embalmed", arresting decomposition and resulting in a preserved specimen known as a bog body. the generally cool and anoxic conditions in these environments limits the rate of microbial activity, thus limiting the potential for decomposition. the time for an embalmed body to be reduced to a skeleton varies greatly. even when a body is decomposed, embalming treatment can still be achieved (the arterial system decays more slowly) but would not restore a natural appearance without extensive reconstruction and cosmetic work, and is largely used to control the foul odors due to decomposition. an animal can be preserved almost perfectly, for millions of years in a resin such as amber. there are some examples where bodies have been inexplicably preserved (with no human intervention) for decades or centuries and appear almost the same as when they died. in some religious groups, this is known as incorruptibility. it is not known whether or for how long a body can stay free of decay without artificial preservation. importance to forensic sciences various sciences study the decomposition of bodies under the general rubric of forensic science because the usual motive for such studies is to determine the time and cause of death for legal purposes: forensic taphonomy specifically studies the processes of decomposition to apply the biological and chemical principles to forensic cases to determine post-mortem interval (pmi), post-burial interval as well as to locate clandestine graves. forensic pathology studies the clues to the cause of death found in the corpse as a medical phenomenon. forensic entomology studies the insects and other vermin found in corpses; the sequence in which they appear, the kinds of insects, and where they are found in their life cycle are clues that can shed light on the time of death, the length of a corpse's exposure, and whether the corpse was moved. forensic anthropology is the medico-legal branch of physical anthropology that studies skeletons and human remains, usually to seek clues as to the identity, age, sex, height and ethnicity of their former owner. the university of tennessee anthropological research facility (better known as the body farm) in knoxville, tennessee has several bodies laid out in various situations in a fenced-in plot near the medical center. scientists at the body farm study how the human body decays in various circumstances to gain a better understanding of decomposition. plant decomposition