ADVANCED EXPERIMENTAL PHYSIOLOGY 95 



plexus innervate separate sets of fibres of the gastrocnemius muscle. 

 Arrange the muscle for the record of a single twitch and make 

 separate records of : -(1) Excitation, minimal and maximal, of the 

 nerve trunk ; (2) similar excitation of each branch of the sciatic 

 plexus ; and (3) simultaneous excitation of both of the branches 

 of the sciatic plexus which supply the gastrocnemius. Compare 

 the results. 



CHAPTER IV 



EXTENSIBILITY AND ELASTICITY OF MUSCLE WHEN AT 

 REST AND CONTRACTED. COMPARISON WITH RUBBER 



Muscle is both extensible and elastic, that is, it can be stretched 

 beyond and will return more or less to its original length when the 

 extending force is removed. These are important properties ; for 

 unless muscle were readily extensible the sudden contraction of 

 one set of muscles would in the body be liable to rupture their 

 antagonists. 



In the study of these properties a gastrocnemius preparation may 

 be used, but a muscle whose fibres run more nearly parallel to each 

 other is preferable, such as a sartorius preparation from a large 

 frog. 



The following experiments should be performed. The bone at the 

 upper end of the preparation is rigidly fixed in a clamp and to the 

 lower end is attached by a short thread or pin a brass mm. scale, 

 having its zero at the bottom. The lower end of the scale has a 

 small tray to carry weights or a hole by which weights can be hooked 

 on. A pointer carried by a separate stand is placed opposite the 

 zero of the scale. A weight of 10 grms. is attached to the scale and 

 the amount of extension read off ; then another 10 grms. are added 

 and so on until the load is 100 grms. or more. It will be found that 

 the length to which the muscle is extended is not proportional to the 

 weight used, but that, by each increase of weight, the muscle is 

 stretched rather less, as shown in Figs. 98, 99, 101. By 

 removing the weights one by one the elasticity of the muscle is 

 observed ; it is not complete ; for when all the weights have been 

 removed the muscle does not at once return to its original length. 

 An " extension-remainder " is present, and this is the more marked 

 the more the muscle is fatigued by the degree and duration of the 

 extension. Therefore the observations should be made as rapidly 

 and on as fresh a muscle as possible. It is probable that muscle in 

 the body with its circulation intact is completely elastic. 



If the muscle is replaced by a suitable piece of rubber band and the 

 same observations are repeated on it, it will be found that the series 

 of elongations are more nearly proportional to the weights used, thus 

 conforming nearly to Hooke's Law, which states that the successive 

 increments in length produced by equal increments of weight are, in 



