214 VETERINARY PHYSIOLOGY 



when it will be found that the first muscle contracts with 

 each contraction of the second, being stimulated by the 

 current of action (Practical Physiology). 



These electrical changes in muscle are of importance — 

 because by means of them the tetanic nature of voluntary 

 contraction of muscle has been demonstrated (p. 230), and 

 because they are now used in the diagnosis of heart disease 

 (p. 428). 



In medicine the string galvanometer is generally used. 

 This consists of a silvered quartz fibre stretched between two 

 powerful magnets. When a current passes through the 

 fibre it is deflected, and the reflected light is thrown upon a 

 moving photographic plate. 



IV. 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 disintegrative 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 may appear in 

 in from 10 minutes to about 7 hours. It generally begins 

 in the head and passes downwards, and it disappears in the 

 same order. 



It lasts for a period which varies with the species of 

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



