214 PHYSIOLOGY 



Inosit (C 6 H 12 6 2H 2 0) or ' muscle sugar ' occurs in minute traces in muscle. 

 It does not belong to the group of carbohydrates at all, being a hexahydrobenzene. 

 It is nonfermentable and does not rotate polarised light nor does it reduce Fehling's 

 solution. Its significance is quite unknown. 



(d) Inorganic constituents. Muscle contains about 75 per cent, of water. A.<h 

 forms 1 to 1*5 per cent, and consists chiefly of potassium and phosphoric acid, with 

 traces of calcium, magnesium, chlorine and iron. 



RIGOR MORTIS 



All muscles after removal from the body, or if left in the body after 

 general death, lose after a time their irritability, and this loss is succeeded 

 by the phenomenon known as rigor mortis. The muscle, which was pre- 

 viously flaccid, contracts, though the shortening is not very powerful and 

 can be prevented by a moderate load on the muscle. Whereas the living 

 muscle is translucent, supple, and extensible, it becomes in the process of 

 rigor opaque, rigid and inextensible. When rigor has been established, 

 the reaction of the muscle is also found to have changed from a slightly 

 alkaline to a distinctly acid one, the acid being due to the presence of sarco- 

 lactic acid. From this condition of rigor there is no recovery. There can 

 be no doubt that the change in consistence of the muscle and probably also 

 its shortening in rigor are due to the coagulation of the muscle proteins. Both 

 changes can be imitated by heating the muscle, as is indicated by Brodie's 

 experiments. This observer found that, if a living muscle be lightly loaded 

 and then warmed very gradually, a series of stages in the heat contraction 

 could be distinguished corresponding to the coagulation temperatures of 

 the different proteins described by von Fiirth in muscle plasma. It seems 

 likely however that the main contraction at all events, that which comes 

 on spontaneously after death or immediately on warming the muscle to 

 450., has another component. In the coagulation of the separated muscle 

 proteins there is no evidence of any appreciable formation of sarcolactic acid, 

 whereas the formation of this substance seems to bear an important relation 

 to the occurrence of rigor. Thus after severe muscular fatigue, as in hunted 

 animals, where there has already been a considerable formation of the waste 

 products of muscular contraction, rigidity may come on almost imme- 

 diately after death. If a thin living muscle be plunged into boiling water, 

 it undergoes instant coagulation, but no chemical change. The reaction 

 of the scalded muscle, like that* of fresh muscle, is slightly alkaline to 

 litmus. No sarcolactic acid or carbonic acid is produced. On the other 

 hand, in surviving muscle, after the cessation of the circulation, there is a 

 steady formation of lactic acid which accumulates in the muscle. The 

 actual coagulation of the muscle proteins occurring in rigor is largely, if not 

 entirely, determined by the increasing acidity of the muscle thereby pro- 

 duced. In fact, it is the production of the acid which causes the onset 

 of rigor, and not the rigor which causes a sudden formation of acid. Hence 

 if the accumulation of lactic acid be prevented by perfusing the muscle 

 with salt solutions, the onset of rigor may be postponed indefinitely, and 

 the muscle may begin to putrefy without having undergone rigor. 



