THE STUDY OF MUSCLE PHYSIOLOGY. 201 



Separation of Muscle from the Central ITervous System.— 

 When the nerve helonging to a muscle is divided, certain his- 

 tological changes ensue, which may be briefly described as 

 fatty degeneration, followed by absorption; and when regener- 

 ation of the nerve-flbers takes place on apposition of the cut 

 ends, a more or less complete restoration of the functions of 

 the nerve follows, but the exact nature of the process of repair 

 is not yet fully agreed upon ; it seems, in fact, to vary in differ- 

 ent cases as to details, though it is likely that, in instances in 

 which there is a complete return to the normal functionally, 

 the axis-cylinders, at all events, are reproduced. 



The degeneration downward is complete ; upward, only to 

 the first node of Kanvier. 



Immediately after the section the irritability of the nerve is 

 increased, but rapidly disappears, from the center toward the 

 periphery (Eitter-Valli law). 



In the mean time the muscle has been suffering. Its irrita- 

 bility at first diminishes, then becomes greater than usual to 

 shocks from the make or break of the constant current ; but 

 finally all irritability is lost, and fatty degeneration and disap- 

 pearance of true muscular structure complete the history. It 

 is theoretically interesting, as well as of practical importance, 

 that degeneration may be delayed by the use of the constant 

 current, the significance of which we have already endeavored 

 to explain. 



The Influence of Temperature,— If a decapitated frog be 

 placed in water of the ordinary temperature, and heat be 

 gradually applied, the animal does not move (proving that the 

 spinal cord alone is not conscious), but the muscles, when 43° 

 to 50° C. is reached, contract and become rigid, a condition 

 known as " heat-rigor." 



There are some advantages in investigating changes in tem- 

 perature by the graphic method. Curves from a muscle-nerve 

 preparation show that elevation of temperature shortens the 

 latent period and the curve of contraction. Lowering the tem- 

 perature has an exactly opposite effect, as might be supposed, 

 and these changes take place in the muscles of both cold- 

 blooded and warm-blooded animals, though more marked in 

 the latter. 



The modifications evident to the eye are accompanied by 

 others, chemical in nature, and a comparison of these shows 

 that the rapidity and force of the muscular contraction 



