68 PHYSIOLOGY FOR BEGINNERS CHAP. 



through the skin, and the skin only, just above the legs, and 

 then sweeping down the skin in one piece, proceeding in the 

 same way that a rabbit or hare is usually skinned. The 

 muscles of the leg will then be laid bare. Any blood pro- 

 ceeding from torn blood-vessels should be wiped away or 

 washed away with water containing a little salt. (0.6 per cent 

 of salt, that is, about one-eighth of an ounce to the pint, is the 

 best, because this is about the amount of salt present in the 

 blood and lymph ; for such a saline solution does not injure the 

 tissues as does distilled or ordinary water.) If the muscles of 

 the frog be not allowed to get dry, but be kept moist with this 

 salt solution, they will remain living tissues for one or two hours. 



Living Muscle and Dead Muscle. Living muscle is 

 semi-transparent, and varies in its redness according to the 

 amount of blood present in its blood-vessels. It is soft and 

 yielding to the touch, and elastic, that is, it stretches when 

 pulled, but returns to its original length when the pull ceases. 

 If a living muscle is pricked by a needle or sharply tapped, 

 it will give a contraction and then at once relax again and 

 remain quiet. Select one of the muscles of the frog, that 

 forming the calf for instance, prick it and see that it contracts. 

 When it contracts it becomes firmer as it increases in girth 

 corresponding to the shortening. The hardness of the muscles 

 of the human limbs, when they are contracted, is familiar to 

 every one. 



Dead muscle, on the other hand, is opaque. It is firm and 

 much less yielding to the touch than living muscle. It is also 

 less elastic. When it is pricked, tapped, or in any way treated, 

 it does not contract, gives no response. 



Out of the substance of living muscle fibres can be squeezed 

 a thick semi-fluid substance, which soon afterwards sets into a 

 jelly, in fact, clots like blood plasma does. This thick liquid 

 which can be squeezed out of living muscle is called muscle 

 plasma. The clot it forms consists of a substance called 

 myosin, corresponding to fibrin formed from blood when it 

 clots, and belonging like it to the class of proteids. When a 

 muscle dies myosin is formed out of the muscle plasma. As the 

 myosin is formed the muscle becomes cloudy and opaque. 

 This you will see as the muscles of the frog gradually die. 

 The myosin also causes the muscles to become firm and 



