248 



ANIMAL MECHANICS. 



greater force, and the attachment of the muscle will he pulled at a much 

 greater velocity. 



In Fig. 132 are two tracings from the gastrocnemius muscle of a frog. 

 The muscle was weighted with 5 grms., and, where a tetanising 



Fig. 132. — Reduced tracings taken from the frog's gastrocnemius muscle by 

 the pendulum myograph. In a a tetanic current was suddenly passed 

 through the muscle. In b the muscle was prevented from contracting 

 until the current had operated for a short time. The upright broken 

 lines mark the position of the path of the lever on a stationary plate. 

 In a the point of the lever is raised to A' in about xi^ °f a second, 

 giving a velocity of about 6 in. per second. In b the point of the 

 lever was raised to the same height (/>') while the plate travelled the 

 distance BB', or in about ^-0- of a second, giving a velocity of about 

 100 in. per second. 



current was passed through it, it raised the point of the lever from the 

 ground line up to A', corresponding to a shortening of the muscle of 

 about - 4 cm. This took place while the plate w T as travelling from 



A to A', a period of about y^ of a 

 second, giving a velocity of about 5 cms. 

 per second. In the case of tracing b, 

 the lever was held for a short time after 

 the tetanising current had passed through 

 the muscle, and then it was suddenly 

 released. It will be noted that the 

 point of the lever attached to it has 

 moved upwards to the same distance, 

 namely, to B', but that it has done so 



ioo Sea. 



Fig. 133. — Reduced tracings taken of 

 the movements of the human finger- 

 tip with the pendulum myograph. 

 Curve a represents the path of a 

 sudden voluntary flexure. Curve b, 

 the path described by the same 



while the recording surface travelled 

 from B to B', which event occupied T J 7r 

 of a second only, giving a velocity of 

 about 80 cms. per second, a velocity 



finger, fixed during the first part of s i x teen times as great as in the first case. 



contraction, and then suddenly re- 



leased. The broken lines sloping 

 upwards are the paths of the finger 

 with a stationary plate. In a the 

 finger is raised to A' (about an inch) 

 during the time that the plate has 

 travelled from A to A', or in about 

 ^ of a second ; its mean velocity 

 is therefore about 33 in. per second. 



We have all found out empirically the 

 fact that the above experiment illustrates, 

 and when we wish to impart great velocity, 

 we check the movement during the initial 

 stages of the muscular contraction. Thus, 

 when we Avish to project a pellet of paper 



In b a movement the same height with considerable velocity, we place it on 

 has occurred while the plate has the tip f the thumb, press the nail of the 

 been travelling from B to B , or in • 1J1 n • , ,-r £J _ i • <• ,i 



about T ^ second. Its velocity is middle fim ? er lnto tlie soft skm of the 

 therefore about 150 in. per second, thumb and behind the pellet; then we 

 or about five times that of a. forcibly extend the middle finger, but do 



not at once release it. 



In Fig. 133 a tracing is made by a style attached to the finger. During 



the movement of the plate the finger is voluntarily bent as quickly as possible. 



The style moved from the ground line to A' during the time the plate travelled 



from A to A' — in about ■£$ second. The second curve represents the path of 



