i GENERAL PHYSIOLOGY OF MUSCLE 15 



and at the same time record the curve of muscular tension. To 

 the first he gave the name of isotonic, to the second of isometric 



curves. 



Isotonic curves are recorded with a very light lever, the weight being 

 applied near the fulcrum by a thread that runs over a wheel during the 

 contraction (Fig. 8). 



The free end of the muscle is attached by a hook and thread to a point of 

 the lever at greater or less distance from the fulcrum. The movements of 

 the muscle are magnified by the writing-point according as the muscle is 

 fixed nearer the fulcrum. Under these conditions the acceleration of the 

 weight is negligible, no matter what the amplitude and speed of the move- 

 ment, and the tension of the muscle remains approximately constant through- 

 out its contraction. 



To obtain relatively perfect isometric curves, the shortening of the muscle 

 must be reduced to a minimum by causing its lower end to work against a 

 strong elastic resistance, and magnifying the excursion of the lever by a long 

 arm (Fig. 9). The muscle is fixed at its upper extremity, and is connected 

 by a long inextensible thread with a metal wheel, to which a steel spring 



Jf 



FIG. 9. Diagram of isometric myograph. The muscle is directly connected with the wheel, which 

 carries the spring M; by pressing on the supports this considerably reduces the rotary 

 movement A, although the latter is magnified by the long arm of the lever L which records it. 



is attached, which rests on a support at its free end. When the muscle 

 pulls on the thread the wheel moves slightly round the axis and the spring is 

 stretched against the support. The least movement of the wheel is magnified 

 by a long light lever, the point of which traces a curve upon a rotating 

 drum that almost perfectly expresses the tension of the muscle during 

 excitation, but not its change of form. 



Various isotonic and isometric myographs have been invented, but the 

 principle is the same as in Figs. 8 and 9. 



When the tension of the muscle remains approximately constant 

 during the course of the contraction (isotonic') the height of the 

 latter generally increases with diminution of the load, at first 

 rapidly, then more slowly, i.e. hot in proportion with the load, 

 while the work done by the muscle, calculated from the weight 

 multiplied by the height to which it is raised, increases within 

 certain limits with each increment of weight (Santesson). 



There are, indeed, exceptions to this rule. According to the 

 observations originally made by Pick, and afterwards confirmed 

 by others, when the weight applied to the muscle is not great, 

 and particularly when an elastic resistance is opposed to the 

 muscle, so that its tension increases constantly during contraction, 



