Preservation of a body is an interesting phenomenon, whether it be the evanescent embalming at a funeral home to prevent the body from decaying at the wake, or preservation for hundreds of years as is the case with Rosalia Lombardo in the Palermo catacombs.
Embalming is a three-fold process of sanitation, presentation and presentation. While the process has ancient roots and is found throughout the world, the modern technique was not possible until the Civil War, when the high number of bodies needing to be shipped over distances necessitated research and led to Dr. Thomas Holmes discovering a method of arterial preservation.
This was later improved in 1867, the August Wilhelm von Hofmann discovered formaldehyde. Primarily it involves the replacement of fluids and blood with chemicals to prevent putrefaction.