CYCLIC MOLECULAR VARIATION 



623 



stimulating force which had raised the substance to b' 

 would, when again applied, after a very brief interval, 

 raise it to b", and so on. That is to say, the molecular 

 effect would in this case be additive. Tetanisation will 

 thus give a curve bearing a great resemblance to the charac- 

 teristic curve. This will be seen from the following record, 

 obtained by magnetic tetanisation of steel (fig. 381), which 

 bears so close a resemblance to the record of electrical 

 tetanisation of nerve (cf. fig. 313). Both these curves, again, 

 resemble the typical characteristic curve seen in fig. 378. In 



FIG. 381. Photographic Record of Magnetic Tetanisation of Steel, 

 exhibiting Transient Enhancement of Response on Cessation 



In a tetanising shocks were moderate, in b strong. 



all these we find that the curve rises, after a longer or shorter 

 horizontality, in an abrupt manner ; that its rate of rise then 

 undergoes a decline, the curve tending again to become 

 horizontal ; after which fatigue-decline may be initiated. In 

 the , photographic record of the magnetic tetanisation of 

 steel (fig. 381), a remarkably suggestive phenomenon is ob- 

 served. In that part of the tetanic curve which is horizontal 

 the one-directioned molecular distortion, due to stimulus, is 

 exactly balanced by the force of restitution. On the sudden 

 cessation of tetanisation the state of balance is disturbed, 

 and we obtain here the remarkable occurrence of a brief 

 overshooting, or positive variation, in the curve, followed 





