METHOD OF MEASURING A MYOGRAM. 



481 



[In studying a muscle-curve, the more or less vertical character of the ascent 

 will indicate the v 



rapidity of the con- 

 traction, the height 

 above the base line, 

 its extent, the length 

 of the curve, the 

 duration, and the 

 line of descent, the - 

 rate of its extensi- " 



f I* ' , Pendulum myograph curve of a frog's gastrocnemius. S, point of stimu- 



01 tUe muscle-curve i at i on . a, latent period ; B, period of shortening, and C, of relaxation. 

 will vary with the 250 DV., tuning-fork vibrating 250 double vibrations per sec. The 

 kind of myograph dotted vertical lines are ordinates (Stirling). 



used ; if it be stationary, then the muscle will merely record a vertical line ; if the 

 recording surface move quickly, the two parts 

 of the curve will form an acute angle (fig. 327) ; 

 and if it move with great rapidity, they will 

 have the form of fig. 325, that obtained with 

 a pendulum myograph. A vibrating tuning- 

 fork records time directly under the tracing, 

 whereby the duration of each part of the curve 

 is readily determined.] 



[In measuring the myogram, all that is required is 

 to know the moment at which the stimulus was ap- 

 plied, and to note when the curve begins to leave the 

 base line or abscissa. Raise a vertical line or ordinate 

 from each of these points, and the interval between 

 these lines, as measured by the chronograph, indicates 

 the time (fig. 325).] 



[The time-relations of a simple muscular con- 

 traction caused by a single induction shock Fig. 326. 

 may be studied by means of the following Arrangement for estimating the time- 



relations during contraction of a 

 muscle produced by a faradic shock. 

 B, battery ; K, key in primary circuit ; 

 I, primary, II, secondary spiral ; I, 

 muscle lever ; e, electro-magnet in 

 primary circuit ; t, electric signal ; St, 

 support ; RC, revolving cylinder (after 

 Rutherford). 



Fix also a Dupre's chrono- 



arrangement : Attach a frog's gastrocnemius to 

 a lever, as in fig. 326, and through the frog's 

 muscle place two wires from the secondary coil 

 of an induction machine. A scale-pan with a 

 weight is attached to the lever. On the same 

 support adjust an electro-magnet with a writing- 

 style in the primary circuit, and in this circuit 

 also place a key (K) to make and break the current 

 graph to the same support, and make 

 it vibrate by connecting it in circuit 

 with a tuning-fork of known rate of 

 vibration, and driven by a galvanic 

 battery. See that the points of all 

 three levers write exactly over each 

 other on the revolving cylinder. The 

 upper lever registers the contraction, 

 the electro-magnet the moment the 

 stimulus is applied to the muscle, and Frog>s muscle stimulat g ed al i eraately by a single 

 the electrical chronograph the time.J break (B) and make shock (M). The lower curve 



[Single make (closing) or break shows the same, but with the muscle fatigued, 

 (opening) induction shocks. A muscle or nerve may be stimulated either with 

 a " make " or " break " induction shock, but it is important to notice that the break 



2H 



