20 PHYSIOLOGY OF MUSCLES AND NERVES. 



angle between the two parts. To mention all the 

 various forms of sockets and the movements which they 

 allow would lead us too far ; it is sufficient to have 

 shown that the action of the muscles is affected by the 

 bones between which they are extended. In order, how- 

 ever, to examine the contractile power of muscles, the 

 latter may be detached from the bones and examined 

 b^ themselves. 



The muscles of warm-blooded animals are but ill- 

 adapted for this purpose ; fortunately, however, those of 

 cold-blooded animals not only possess the same qualities, 

 but retain the power of contraction long after their re- 

 moval from the animal, a circumstance which renders 

 them very valuable for purposes of study. The frog is 

 most frequently used in such experiments, both on 

 account of its common occurrence and of the power of 

 its muscles. If a frog is beheaded and an entire muscle 

 is cut from either its upper or lower thigh, one of the 

 tendons of this muscle may be fixed in a vice, and 

 its other tendon may be connected with a lever, re- 

 presenting as it were the bone, by the motion of which 

 the contraction of the muscle may be studied.^ Weights 

 may also be attached to this lever in such a way that 

 the burden which the muscle is capable of lifting may 

 be studied. It will at once be observed that the muscle 

 is extended when such weights are attached, and is 

 extended more in proportion as the weight attached 

 is heavier. This results from the elastic qualities of 

 muscle ; and before examining the contraction of muscles 

 it will be necessary carefully to study their elasticity. 



' In order to fasten tlic muscle more securely, it is generally 

 well to leave a small piece of the bone at either end attached to the 

 tendons, and to fasten the muscle by these. 



