IRRITABILITY AND CONDUCTIVITY 175 



Minimal and Maximal Stimuli ; Threshold Value. 



Arrange the gastrocnemius muscle to write on 

 a smoked drum. Connect one binding post of 

 the secondary coil to the muscle clamp, the 

 other binding post to the post on the muscle 

 lever. Load the muscle with 10 grams. De- 

 scribe an abscissa on the smoked paper, turning 

 the drum by hand. Send a feeble break induc- 

 tion current through the muscle. 



There will be no response. 



Kepeat the break currents, gradually moving 

 the secondary closer to the primary coil. 



At a certain point the muscle will just con- 

 tract (" threshold value "). This is a minimal 

 contraction produced by a minimal stimulation. 



Turn the drum 5 mm., move the secondary 

 coil 5 mm. nearer the primary, send in another 

 break current, and record the contraction. Con- 

 tinue this. 



The contraction in answer to each break cur- 

 rent increases with the strength of the currents 

 at first rapidly, then slowly, up to a certain point. 

 Further increase in the strength of the stimulus 

 produces no further increase of contraction. The 

 stimulus and the resulting contraction have now 

 become maximal. 



There is a striking disproportion between the 

 energy of the stimulus necessary to throw a 



