THE CHEMICAL CHANGES IN MUSCLE 239 



tissues. Its significance we shall discuss later on when inquiring into 

 the history of the proteins in the body. 



Other nitrogenous extractives are : 



Hypoxanthine or sarcine, xanthine (both bodies allied to uric 

 acid), and a trace of urea. 



(c) NON- NITROGENOUS CONSTITUENTS. Fats. 



Glycogen. The amount of this is very variable. In the embryo 

 the muscles may contain large quantities, but in the adult they contain 

 only from 04 to 1 per cent. 



Inosit (C 6 H 12 6 -+- 2H 2 0), or ' muscle- sugar,' which occurs in 

 minute traces, is non-fermentable, does not rotate polarised light, and 

 does not reduce Fehling's solution. It does not belong to the group 

 of carbohydrates at all, being a derivative of benzene. 



Dextrose. It is doubtful whether this is present in fresh resting 

 muscle. 



(r>) INORGANIC CONSTITUENTS. Muscle contains about 75 per- 

 cent, of water. The ash forms 1 to 1-5 per cent, and consists chiefly 

 of salts of potassium and phosphoric acid. There are small traces of 

 calcium, magnesium, chlorine, and iron. 



RIGOR MORTIS 



All rnu5bles, within a short time of their removal from the body, 

 or if left in the body after general death, lose their irritability, and 

 this is succeeded by an event which occurs rather suddenly, and is 

 known as rigor mortis. The muscle, which was before translucent, 

 supple, extensible, becomes more opaque, rigid, and inextensible, and 

 shortens. The shortening is not very powerful, and can be prevented 

 by loading the muscle moderately. Chemical changes also take place. 

 The muscle, which was previously alkaline, becomes distinctly acid, 

 the acidity being due to the formation of sarcolactic acid. There is 

 also production of C0 2 with evolution of heat. 



It is generally believed that this change is identical with the 

 clotting of muscle-plasma, and that the rigidity as well as the contrac- 

 tion of the muscle is due to the coagulation of the muscle-proteins. 

 That there is at any rate a close connection between the two sets of 

 phenomena is shown by Brodie's experiments. This observer found 

 that, if a living muscle be lightly loaded and then warmed very gradu- 

 ally, a series of stages in the heat-contraction could be distinguished 

 corresponding to the coagulation temperatures of the different proteins 

 described by von Furth in muscle-plasma. It seems likely, however, 

 that the main contraction at all events, that which comes on sponta- 

 neously after death or immediately on warming the muscle to 45 C., 

 has another component. In the coagulation of the separated muscle - 

 proteins there is no evidence of any appreciable formation of sarco- 



