XXXVI.] ISOTONIC AND ISOMETRIC CONTRACTIONS. 20$ 



recorder" devised by Fick (fig. 123). One end of the muscle is 

 fixed, the other is attached Idj means of an inextensible thread 

 which passes round a small pulley fixed on a steel axis (A). This 

 axis carries (i) a long light recording lever (Z), and (2) a hori- 

 zontally placed steel spring (F) whose free end rests on a support 

 (w). When the muscle contracts, the spring (F) is pressed against 

 the support (u). In consequence of the opposing tension of the 

 spring the axis can only be turned slightly, but this movement is 

 greatly amplified by the recording lever. 



Schonlein has devised a myograph (Pfliiger's ArcTiiVy Bd. 52, p. 

 112), which is so arranged that one can record either isotonic con- 

 tractions or isometric contractions. The isometric curves so 

 obtained have been called " tonograms." The apparatus is made 

 by W. Siedentopf in Wiirzburg. 



3. Work Done duiing a Single Contraction. — Arrange a gastroc- 

 nemius to record on a cylinder, but record only the " lift," as in 



Z ^ ^ 



T? 



FiO. 123.— Scheme of Fick's Tension-recorder. A. Axis movement ; F. Strong spring 

 resting on support u ; Z. Writing-lever. 



Lesson XXXIV., the cylinder being stationary, moving the 

 cylinder with the hand as required. On the lever under the 

 muscle attachment place a scale-pan, and in this place weights of 

 known value. With each twitch the muscle lifts the weight, and 

 thus does a certain amount of work which is easily calculated 



{a) Measure the height of the tracing from the base line or 

 abscissa. This is conveniently done by a paper millimetre scale 

 fixed to a microscopic slide. The work done (W) is equal to the 

 weight {w) lifted multipHed by the height (//) to which it is lifted — 



W = m;A. 



But, of coui-se, a long lever being used, the tracing is much higher 

 than the actual shortening of the muscle. 



{h.) To determine the exact amount of the lift, one must know the 

 length of the lever and the ratio between its arms. Suppose the 

 one to be ten times as long as the other, then the total work in 

 gram-millimetres must be divided by 10. 



