THE MECHANICAL RESPONSE 3 



direction, say to the right. The extent of this pull 



depends on the amount of contraction. A band of 



paper or a revolving drum-surface moves at a uniform 



speed at right angles to the direction of motion of the 



writing lever. When the muscle recovers from the 



stimulus, it relaxes into its original form, and the writing 



point traces the recovery as it 



moves now to the left, regaining 



its first position. A curve is thus 



described, the rising portion of 



which is due to contraction, and 



the falling portion to relaxation 



or recovery. The ordinate of the 



curve represents the intensity of 



response, and the abscissa the time , 



FIG. 1. MECHANICAL LEVER 



. 1). BECORDER 



r*hnf n/*f A-iefiVo e\f f VIA t- AonrmoA The muscle M with the attached 



Characteristics 01 tne response- bone is sec urei y held at one 



(t\ P*rinH (?\ AtnnlifiiH** end, the other end being con- 



(I) f eriOd, (2) Amplitude, nected with the writing lever. 



(3) Form.-Just as a wave of sound 

 is characterised by its (1) period, 



(2) amplitude, and (3) form, so surfa. ra wh?n 



.-, , ,. cle recovers from contrac- 



these response-Curves be dlS- tion,thetracingpointreturns 



" to its original position. See 



trom each Other. AS on P the record of muscle 



_ . curve. 



regards the period, there is an 



enormous variation, corresponding to the functional 

 activity of the muscle. For instance, in tortoise it may 

 be as high as a second, whereas in the wing-muscles of 

 many insects it is as small as -^^ part of a second. 

 * It is probable that a continuous graduated scale might, 

 as suggested by Hermann, be drawn up in the animal 

 kingdom, from the excessively rapid contraction of 



B 2 



