MUSCULAR CONTRACTION AND MYOGRAPHS. 



477 



do so more rapidly than the doubly refractive discs. The total volume of each element 

 does not undergo any appreciable alteration in volume during the contraction. Hence, the 

 doubly refractive discs increase in volume at the expense of the singly refractive. From this 

 it is concluded that, during the contraction, fluid passes from the singly refractive into the 

 doubly refractive discs ; the former shrink, the latter swell. 



MerkeFs view is partially different. In fig. 319, 4, are two muscular elements at rest ; in (5), 

 two in a state of contraction, after Merkel. The grey punctuated areas are the doubly refrac- 

 tive substance, c, the median disc. According to Merkel, during contraction the dark substance 

 lying in the middle of the element changes its position either in part or as a whole ; it leaves 

 the middle of the element (the two surfaces of Hensen's median discs, 4, c), and places itself 

 at the lateral discs, 5 at e and d, while the clear substance leaves the lateral disc, 4, e and d, 

 and applies itself to both surfaces of the median disc, 5, c. The clear substance of the isotrop- 

 ous discs is fluid, and plays a more passive role ; during contraction it is in part absorbed by 

 the dark substance which thus swells up. This mutual exchange of place of the substances is 

 accompanied by an intermediate "stage of dissolution" in which the whole contents of the 

 element appear equally homogeneous, in which, therefore, the fluid singly refractive substance 

 has uniformly penetrated the doubly refractive substance. At this moment only the lateral 

 discs are still visible. 



[If a living portion of an insect's muscle be examined in its own juice, contraction- waves 

 may be seen. to pass over the fibres. When a contraction- wave passes over part of the fibres, 

 the discs become shorter and broader ; at the same time, in the fully contracted part, the dim 

 disc appears lighter than the centre of the light disc. There is said to be a " reversal of the 

 stripes " from Avhat obtains in a passive muscle. Before this stage is reached, there is an inter- 

 mediate stage where the two bands are almost uniform in appearance.] 



Methods. These phenomena are best observed by "fixing" the different stages of rest or 

 contraction, by suddenly plunging the muscular fibrillse of insect's muscles into alcohol or 

 osmic acid, which coagulates the muscle-substance. The actual contraction may be observed 

 under the microscope in the transparent parts of the larvae of insects. 



Spectrum. A thin muscle, e.g., the sartorius of the frog, when placed directly behind a 

 narrow slit running at right angles to the course of the fibres, yields a diffraction-spectrum. 

 When the muscle contracts, as by me- 

 chanical stimulation, the spectrum 

 broadens, a proof that the interspaces of 

 the transverse stripes become narrower 

 {Ranvier). 



298. MUSCULAR CON- 

 TRACTION. Methods. In 



order to determine the duration 

 of each phase of a muscular con- 

 traction, myographs of various 

 forms are used. 



V. Helmholtz's Myograph is shown 

 in fig. 320. A muscle, M say the 

 gastrocnemius of a frog attached to the 

 femur is fixed by the femur in a clamp, 

 K ; its lower end is attached to a mov- 

 able lever carrying a scale-pan and 

 weight, W, the weight being varied at 

 pleasure. When the muscle contracts, 

 necessarily it raises the lever. At the -pig 320. 



free end of the lever is a movable style, s h f Helmholtz's myograph. M, muscle fixed 



F, which inscribes its movements on a . d K F rfti ^ ; P, weight or counter- 



revolving cylinder caused to rotate at a f * A ] ' . w s *{ lian for weights S S 



uniform rate by means of clock-work. W*J fo r the lev'er P g ' 



The cylinder is covered with smoked FF , 



enamelled paper in the flame of a turpentine lamp. When the muscle contracts, it inscribes a 

 curve the " muscle-curve," or " myogram." The abscissa of the curve indicates the duration 

 of the contraction, but of course the rate at which the cylinder is moving must be known. The 

 ordinates represent the height of contraction at any particular part of the curve. 



The muscle-curve may be inscribed upon a smoked glass plate attached to one limb of a 

 vibrating tuning-fork. Such a curve registers the time-units in all its parts. Suppose each 

 vibration of the tuning-fork = 0*01613 second, then the duration of any part of such a curve is 

 obtained by counting the number of vibrations and multiplying by 0*01613 second. 



[Fick's Pendulum Myograph. A board fixed to the wall carries a heavy iron pendulum, P, 



