20 EXPERIMENTAL PHYSIOLOGY. 



muscle is independently irritable for the nervous impulse has 

 been ruled out. This has been accomplished by paralysis of 

 the tissue connecting nerve fibres with muscle fibres, for it 

 can be shown that impulses still travel along the nerve. How 

 does this experiment show the locus of action of the drug curare? 



EXTENSIBILITY AND ELASTICITY OF MUSCLE. 



In the body more or less tension affects each muscle. The 

 weight of various parts and the antagonistic action of opposing 

 muscles contribute to this tension. The result is a certain amount 

 of elongation. This can be shown by fastening a weight to an 

 isolated muscle. When the weight is removed the muscle soon 

 regains its former length, that is, it exhibits elasticity. 



The amount of elongation increases with increase in tension, 

 but with each additional tension the elongation is proportionately 

 less. To illustrate suppose X grams cause an elongation of 2 mm. 

 Then 2 X grams will not cause 4 mm. elongation but something 

 less, perhaps 3 mm. 3 X grams would produce 4.5 mm. elonga- 

 tion, etc. 



Beyond a certain tension the reverse is true; the elongations 

 per unit increase being greater and greater with each step. Where 

 this reversal begins the so-called elastic limit has been passed. 

 Finally there comes a time when the muscle fibers are ruptured. 



Needless to say a muscle should not be extended beyond its 

 elastic limit. 



In conclusion, tension is very useful in keeping a muscle pre- 

 pared for contraction, for we find that a muscle will not only 

 respond more quickly but more energetically if it is under a certain 

 amount of tension. This condition holds in the body. 



Muscle can be stretched and again regain its resting length 

 when the force producing the change is removed. It differs some- 

 what from a rubber band in that it does not respond by equal 

 extension for equal increments of weight as the total weight in- 

 creases nor does immediate recovery occur when the weights are 

 removed. 

 Experiment 6. Isolate either of the two large muscles (gracilis 



and semi-membranosus, Fig. 4) on the inside of the thigh of a 



