The usual explanation that is given of rigor is that it is due to a coagulation of the fluid substance, the muscle plasma, of which the fibers are constituted. During life the fluids exist in a liquid or viscous condition; after death they coagulate into a solid form.
Rigor mortis is not a sign of death, as there is rigidity of the muscles following apparent death, as in cases of asphyxia and trance. If the body is rigid, in a case in which there is a doubt that death is present the rigidity may be broken up. If it is a case of trance or that of the contraction of the muscles following drowning, it is likely to return, especially in case of trance; but if death is actually present it will not return.
The chemical changes occurring, the result of rigor mortis can be briefly stated:
(a) There is a coagulation of the proteid material of the muscle plasma.
(b) There is an increased acidity, which is doubtless due to the production of lactic acid.
(c) There is a production of carbon dioxide.
(d) There is a consumption of glycogen.
Treatment by the Embalmer.—Many times when called to embalm a subject you will find the body in a state of rigor. In cases of this kind the rigor mortis should be broken up. This can be done by taking each of the joints and gradually bend them a little at a time until they become perfectly lax. Once a joint is bent the stiffening disappears and the embalmer can proceed.
Fermentation and the Production of Gas.
—A molecule is the smallest portion of a compound which can exist by itself.