30 



EXPERIMENTAL PHYSIOLOGY 



Finally, take a tuning-fork tracing below the abscissa. 

 Notice the effect of heat and cold respectively upon the period of 

 latency and upon the amount and duration of the contraction. 



Isometric contraction. If the contracting muscle is prevented from shorten- 

 ing, or allowed only to shorten to so small an extent so that it practically re- 

 mains of the same length throughout, the contraction is said to be isometric. 

 It is recorded by attaching the muscle very close to the fulcrum of the muscle 

 lever, which is held down by a strong spiral spring (fig. 34) instead of by a weight. 

 All the other arrangements of the experiment are the same as with the ordinary 

 method where the muscle is free to shorten and raise a weight ; its tension 

 being constant (isotonic contraction). 



FIG. 34. METHOD OP STUDYING ISOMETRIC CONTRACTION, sp. SPIRAL SPRING ; 



s. SCREW FOR REGULATING ITS TENSION. 



Action of drugs on muscular contraction. The hyoglossus muscles may be 

 used. Cut away the whole of the lower jaw, along with the tongue and hyoid 

 bone. Tie a thread to the tongue near its tip and another near its fixed ex- 

 tremity, and cut this away from the hyoid. The tongue thus separated includes 

 the hyoglossus muscles, which run through it from the hyoid bone, and the pre- 

 paration can be used in the same way as the gastrocnemius muscle, the hyoid end 

 being fixed by a pin to the myograph cork and the tip connected by its thread 

 with the myograph lever. A smaller weight must be used than in the case of 

 the gastrocnemius, since the hyoglossus muscles are far weaker. Probably the 

 weight of the lever alone will be sufficient. Insert pin electrodes on either side 

 near the fixed end so that induction shocks will stimulate all the fibres of both 

 hyoglossus muscles. 



Veratrin. Arrange the apparatus to take a muscle curve in the 



