EXCITATION OF MUSCLE 



193 



duration, the break stimulus is ineffective ; so in both cases, whether 

 we make or break the current in the primary circuit, we are dealing with 

 a make stimulus in the muscle. The difference in the efficacy of make and 

 break induction shocks is purely physical, and depends on the fact that the 

 current induced in the secondary coil on make is of slower rise and smaller 

 potential than that produced at break. 



In using either of these modes of stimulation we find that there is a certain intensity 

 which the stimulating current must possess in order that any effect shall be produced. 

 Any strength of stimulus below this is known as a subminimal stimulus. A minimal 

 stimulus (sometimes known as liminal or threshold stimulus) is the weakest stimulus 

 that will produce any result, i.e. in muscle a contraction. A maximal stimulus is 

 one that produces the strongest contraction a muscle is capable of under the effects 

 of a single stimulus. A submaximal stimulus is any strength of stimulus between these 

 two extremes. 



