i GENEKAL PHYSIOLOGY OF MUSCLE 7 



do not correspond with the true movements of the excited muscle. Owin" 

 to the weight of the lever and the distance from the axis of the load applied 

 to the muscle, the entire mass 

 is accelerated on the rapid con- 

 traction of the muscle, and the 

 curve altered, because the ten- 

 sion in the muscle due to the 

 load is greater at first, and then 

 gradually diminishes instead 

 of being constant. To avoid this 

 the mass raised by the muscle 

 and the height to which it is 

 lifted must be lessened, so as 

 to obviate changes of tension 

 during the contraction. This 

 is done by using a very light 

 lever, and making the height 

 to which the weight is raised 

 as small as possible by attach- 

 ing it, close to the fulcrum, to 

 a thread which passes over a 

 wheel fixed at the axis of the 

 lever. By this arrangement 

 the acceleration imparted to 

 the weight becomes negligible, 

 no matter how rapid and ample 

 the movement of the lever, and 

 the passive tension of the muscle 

 remains constant throughout 

 the experiment. F IG . I. Pflliger's myograph. Explanation in text. 



Fig. 2 (which is only a modi- 

 fication of Waller's myograph) gives one of many that have been constructed 

 on this principle. It is adapted to show on the same muscle the effects 



Fin. 2. Myograph for comparing direct and indirect excitation on the same muscle loaded or 

 unloaded. (Luciani.) The frog's gastrocnemius muscle is fixed horizontally over the surface 

 of the mercury contained in a hollow of the cork plate. It is connected by a thread with a 

 jointed lever 11, the axis of which carries a small wheel ; a thread passes round this to hold 

 the scale-pan for the weight p, which is to load the muscle. The vertical arm of the aluminium 

 lever, on which the muscle pulls directly, works the movements of the much longer horizontal 

 arm, which consists of a straw ending in a writing-point, by which the movement is traced 

 on a revolving cylinder. The relations between the two arms can be easily adjusted. The 

 electrodes from the secondary coil of an induction apparatus can be applied by a Pohl's 

 commutator without cross- wires to the muscle or the nerve, according as the bridge is thrown 

 over to the left M, or right N. 



not only of direct and indirect excitation, but also of different weights 

 applied to the muscle, from the minimal load of a fine straw employed as 



