SKELETAL MUSCLE 



69 



over them. Break the connection just mentioned and 

 the muscle is paralyzed. For experimental purposes 

 we may substitute artificial stimuli for the normal ones 

 which proceed from the brain and cord. Electric 

 shocks are generally employed in such trials. They are 

 preferable for several reasons to other kinds of stimuli. 

 They are relatively harmless to the tissue and they can 

 be accurately graded in intensity. 



To study the nature of muscle contraction an isolated 



dr 



FIG. 14. m is the muscle held in a clamp and connected with a 

 weighted lever the point of which bears on the smoked drum, dr. n 

 is the nerve carried over electrodes through which it can be stimulated. 

 Stimulation may be applied directly to the muscle. 



muscle from a frog's leg is usually chosen. The most 

 suitable for most uses is the gastrocnemius since it is 

 readily separated, with little or no injury, from the 

 neighboring structures. It is left attached above to a 

 bit of the thigh-bone which is held in a clamp. The 

 tendon below is made fast to a lever which the muscle 

 will lift when it contracts. The lever is designed to 

 reproduce the movements of the tendon upon a larger 

 scale. At its free end it is tipped with a point of paper 



