ELEMENTARY EXPERIMENTAL PHYSIOLOGY 53 



Secondary Tetanus. If the nerve be stimulated with a rapid series 

 of induction-shocks the muscle B goes into tetanus and its * currents of 

 action ' stimulate the nerve A, with the result that the tetanus is also 

 observed in the muscle A. This ' secondary tetanus ' can be produced 

 by rapid mechanical stimuli. 



Further experiments upon the electromotive properties of muscle 

 and nerve are given in Chapter XXIII. 





CHAPTER XII. (Advanced). 



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 or better 

 still a gracilis-semimembranosus preparation. 



A gracilis-semimembranosus preparation consists of the two large 

 internal thigh muscles (Figs. 2Q, 21). The gracilis is a large muscle lying 

 along the inner side of the sartorius ; it arises from the ischial sym- 

 physis and is inserted into the head of the tibia. The semimembranosus 

 is a bulky muscle behind the gracilis on the posterior aspect of the thigh ; 

 it also arises from the ischial symphysis and is inserted into the back of 

 the head of the tibia. To make the preparation, isolate these two muscles 

 from those surrounding them near their points of insertion, cut through 

 the tibia below this point and through the femur just above the knee 

 joint. Holding this piece of bone, separate the two muscles up to the 

 symphysis and remove with them the bone from which they arise. If 

 a larger or longer muscle still is required, a double preparation may be 

 made with the muscles of both thighs and the two hung side by side, or 

 one below the other, united in the middle by the piece of the symphysis. 



The following experiments should be performed. The bone at the 



