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THE FUNCTIONS OF CROSS-STRIATED MUSCLES 



2. THE PROPERTIES OF RESTING MUSCLE 

 A. ELASTICITY 



If a metallic wire vertically suspended be loaded with a certain weight, 

 almost immediately it assumes the maximum length for that load and, prac- 

 tically speaking, is not extended further however long the weight remains. 

 A muscle or other organic tissue behaves very differently. If we load a fresh 



muscle with a weight, for a moment it 

 takes a certain length according to the 

 size of the load, but thereafter as long 

 as the weight remains it continues to 

 stretch, at first rapidly and then more 

 and more slowly. This secondary stretch- 

 ing is spoken of as the after extension. 

 When a muscle already stretched by a cer- 

 tain weight is unloaded, it shortens rap- 

 idly at first, then more and more slowly. 

 In this case it is said to exhibit secondary 

 elasticity, or after shortening (Fig. 150). 



These secondary phenomena render the 

 investigation of the elasticity in muscles 

 and the influence of load rather difficult. 

 In order to reduce the effect of after exten- 

 sion as much as possible, Marey and Blix 



have hit upon a device by which the load can be increased or diminished contin- 

 uously and very rapidly, and the variations in length of the muscle can be 

 recorded at the same time (Fig. 151). 



The support (i) bears the muscle lever (c) on which the muscle is fastened 

 at m. The lever is loaded by means of the weight 7i, and is counterbalanced by 

 the weight ~k. The plate (f) with the recording surface (I) attached to it can 

 be moved back and forth between the two ledges screwed fast to the base. At 

 the same time the weight h controlled by the bar & is moved along the lever, 



FIG. 150. Curves representing the ex- 

 tension, A, and elastic shortening, 

 B, of two adductor muscles, after 

 Blix. A was suddenly loaded with 

 100 g. of weight and B was sud- 

 denly relieved of its weight. 



FIG. 151. Apparatus of Blix and Lov6n for recording the elasticity curve of a muscle. 



and in this way the load acting on the muscle is changed in proportion to the 

 excursion of the writing surface. Curves obtained with the apparatus represent 

 the extensibility and elasticity of the muscle with a uniformly increasing and 

 uniformly diminishing load. 



