THE MECHANICAL CHANGES OF MUSCLE 



197 



inertia, be a very inaccurate reproduction of the true events occurring in the muscle 

 itself. When the muscle begins to contract it imparts a very rapid movement to the 

 lever, which therefore tends to overshoot the mark and deform the curve. This source 

 of error may be almost avoided by making the lever as light as possible, and hanging the 

 extending weight in close proximity to the axle of the lever, as shown in Fig. 55. Since 

 the energy of a moving mass is proportional to the square of the velocity ( = %mv 2 ,) 

 and the tension due to the weight as well as the velocity on contraction is directly 

 proportional to the distance of the weight from the axis, it follows that it is better to 



Ct_ 



r 



FIG. 55. Blix apparatus for recording isometric and isotonic curves synchronically. (Miss 

 BUCHANAN.) p, the steel cylindrical support with jointed steel arm to bear the isotonic 

 lever I, which consists of a strip of bamboo with an aluminium tip. t, the isometric 

 lever, also of bamboo, except for a short metal part t', in which are holes for fixing the 

 muscle. The two wires from an induction coil are brought, one to X , which is in con- 

 nection with the support and hence with the metal bar t', the other to y, which is insulated 

 from the support but connected by a copper wire with a thin piece of copper surrounding 

 the isotonic lever at the point where the muscle is attached to it. Cl, clamp for fixing 

 the lower end of the muscle when an isometric curve is to be taken. The axis of the 

 isotonic lever is at x, close to 'which is hung the weight of 50 grm. 



oad the muscle with 40 grams 1 millimetre from the axis than with 1 gram 40 milli- 

 etres from the axis, though the tension put on the muscle will be the same in both 

 ases. 



In the first case the energy of the moving t mass, will be proportional to 



0}- 

 L = 800, and it is this energy which deter- 



) X (I) 2 1 



= 20, and in the second to 



nines the overshooting of the lever and the deformation of the curve. Since throughout 

 le contraction in the latter arrangement the lever follows the muscle in its movement, 

 le tension on the muscle remains the same throughout, and the method is therefore 



:nown as the isotonic method. 



It is of importance to be able to record the development of the energy (i.e. the ten- 

 on) of the active muscle apart from any changes in its length. For this purpose the 

 luscle is allowed to contract against a strong spring, the movements of which are 

 lagnified by means of a very long lever. Thus the shortening of the muscle is almost 

 ntirely prevented, but the increase in its tension causes a minute but proportionate 

 lovement of the spring, which is recorded by means of the lever. Since in this case 

 ae length or measurement of the muscle remains approximately constant, while the 

 3nsion is continually varying throughout the contraction, it is known as the isometric 

 lethod. The great magnification necessary in this method introduces serious sources of 

 rror ; but it seems that if all due precautions be taken to avoid these errors, the isometric 





