72 VETERINARY PHYSIOLOGY 



so that the record of a series of contractions has a somewhat 

 stair-like appearance. 



5. A series of stimuli do not cause a tetanus, but simply 

 increase the rapidity and force of the individual contractions. 



Cardiac Muscle physiologically resembles other visceral 

 muscles, but its period of contraction is shorter and its 

 rhythm generally more rapid. 



4. 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 neerobiotie 

 changes begin. The first of these Rigor Mortis is a disin- 

 tegrative 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 does not generally alter the position of the 

 limbs, although it may sometimes 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 becomes limp. 

 In all probability this latter change is due to a solution of 

 the myosin by an enzyme like that of the stomach pepsin 

 which seems to exist in all the tissues. This can act only 

 in the presence of an acid, and the appearance of sarcolactic 

 acid, therefore, allows it to come into play. 



