In addition to the varnas, there is a fifth class in Hinduism. It encompassed outcasts who, literally, did all the dirty work. They were referred to as "untouchables" because they carried out the miserable tasks associated with disease and pollution, such as cleaning up after funerals, dealing with sewage, and working with animal skin.
Brahmins were considered the embodiment of purity, and untouchables the embodiment of pollution. Physical contact between the two groups was absolutely prohibited. Brahmins adhered so strongly to this rule that they felt obliged to bathe if even the shadow of an untouchable fell across them.
