74 HUMAN PHYSIOLOGY 



deprived of all free oxygen by placing it in the receiver of 

 an air pump, and then transferred through mercury to an 

 atmosphere of nitrogen, still continues to produce carbon 

 dioxide. This means that its oxygen must be intramolecular, 

 must be in the muscle molecule, like the oxygen of nitro- 

 glycerine. Probably the presence of this oxygen is one of 

 the causes of the instability of the molecule. 



The muscle then takes these substances into itself makes 

 them part of its molecule assimilates them before breaking 

 them down. It is not necessary to suppose that all the 

 substances are equally intimately associated with the muscle 

 protoplasm. In all probability the proteid becomes much 

 more truly a part of the muscle than the carbohydrates and 

 fats, but with each one of them it is essential that it should 

 come into the domain of the muscle and not simply remain 

 in the blood and lymph, in which it cannot be used. 



5. DEATH OF MUSCLE. 



The death of the muscle is not simultaneous with the 

 death of the individual. For some time after somatic death 

 the muscles remain alive and are capable of contraction 

 under stimulation. Gradually, however, their irritability 

 diminishes and finally disappears. They are then dead, 

 and necrobiotic changes begin. The first of these Rigor 

 Mortis is a disintegrate chemical change whereby carbon 

 dioxide and sarcolactic acid are set free, and at the same 

 time the soluble myosinogen changes to the insoluble myosin 

 and the muscle becomes contracted, less extensile, less elastic, 

 and more opaque. The contraction is a feeble one, and since 

 it affects flexors and extensors equally, it is not generally 

 able to alter the position of the limbs, although it may some- 

 times do so. As these changes occur, heat is evolved and the 

 muscles become warmer. 



The time of onset of rigor varies with the condition of the 

 muscles. If they have been very active just before death, 

 stiffening tends to appear rapidly. 



It lasts for a period which varies with the species of 

 animal and with the condition of the muscles, and as it 

 disappears the muscles again become soft, and the body 



