Tissue gas is the name given to the action of the bacteria Clostridium perfringens

Clostridium perfringens

Clostridium perfringens is a Gram-positive, rod-shaped, anaerobic, spore-forming bacterium of the genus Clostridium. C. perfringens is ever present in nature and can be found as a normal component of decaying vegetation, marine sediment, the intestinal tract of humans and other vertebrates,...

(formerly known as C. welchii) in dead bodies. Its effect on the deceased is that of an extremely accelerated decomposition

Decomposition

Decomposition is the process by which organic material is broken down into simpler forms of matter. The process is essential for recycling the finite matter that occupies physical space in the biome. Bodies of living organisms begin to decompose shortly after death...

. It is only halted by embalming

Embalming

Embalming, in most modern cultures, is the art and science of temporarily preserving human remains to forestall decomposition and to make them suitable for public display at a funeral. The three goals of embalming are thus sanitization, presentation and preservation of a corpse to achieve this...

 the body and special additive chemicals must be employed. It most commonly occurs in the bodies of people who have died of gangrene

Gangrene

Gangrene is a serious and potentially life-threatening condition that arises when a considerable mass of body tissue dies . This may occur after an injury or infection, or in people suffering from any chronic health problem affecting blood circulation. The primary cause of gangrene is reduced blood...

, large decubitus ulcers, necrotising fasciitis or who have had soil, faeces or water forced into wounds.