4i 8 A MANUAL OF VETERINARY PHYSIOLOGY 



hypoxanthine (obtainable in the free form in muscle extracts), 

 xanthine, carnine, taurine (in horse-flesh), uric acid in minute 

 traces (though more abundant in reptilian muscle), and traces 

 of urea, though this is a question still not decisively settled. 

 Of these kreatin is by far the most important ; it is a substance 

 which has already been studied in connection with the production 

 of urea (p. 325). The ash in muscle consists principally of the 

 salts of potassium and magnesium. The gases are carbon dioxide, 

 together with a small amount of nitrogen, but no free oxygen. 

 In plain muscle glycogen is only found in traces, if at all ; 

 lactic acid and kreatin are found in smaller quantities than in 

 striped muscle. Hypoxanthine is conspicuously present. As 

 just stated, potassium and magnesium furnish the chief salts of 

 striped muscle, while salts of sodium and calcium represent those 

 of plain muscle. 



Rigor Mortis. — After death a muscle passes into the condition 

 of rigor or stiffening, by which it changes both in its physical and 

 chemical aspect. The muscle becomes firm and solid, loses its 

 elasticity, and no longer responds to electrical stimuli ; further, 

 it loses its alkaline reaction, and in course of time becomes acid 

 owing to the formation of sarcolactic acid. Through the death 

 of the muscle its proteins pass from a fluid or viscous condition 

 into a solid, and this process is generally believed to be identical 

 with the clotting of muscle-plasma previously described. Rigor 

 mortis and the production of sarcolactic acid are closely con- 

 nected, so that if the formation of the acid be prevented by suit- 

 able means, rigor does not occur. The view now adopted as to 

 the cause of death-stiffening is that it is due to a coagulation of 

 the proteins by the products of metabolism in the muscle, and 

 this explanation accounts for the rapid setting in of rigor in 

 animals hunted to death. Rigor mortis is delayed in a rabbit in 

 which the labyrinth of the internal ear has been destroyed. This 

 is probably connected with the obscure problem of muscle tonus, 

 with which the labyrinth is connected. The muscles in which 

 delayed rigor mortis occurs are those corresponding to the same 

 side of the body as the injured labyrinth. During rigor mortis 

 carbon dioxide is produced and heat evolved ; some after-death 

 temperatures are remarkably high. After a certain length of 

 time rigor mortis passes off and decomposition commences. 



There is a condition of muscle known as heat rigor, which is 

 produced by rapidly raising the temperature of a mammalian 

 muscle to 47 C. (117 F.). It is very closely allied to death 

 rigor, and is due to the same cause — viz., coagulation of the 

 proteins. It differs from death rigor inasmuch as it does not 

 pass away. 



It is doubtful whether rigor mortis occurs in involuntary 



