MUSCULAR TISSUE. 243 



move the skin from both hind legs and expose the sciatic nerve in 

 one of them. Insert a small wire hook through the jaws of the 

 frog and suspend the animal from an ordinary clamp or iron ring. 

 Pass electrodes under the exposed sciatic nerve, and after tying 

 the other leg to prevent any muscular movement, stimulate the 

 exposed nerve by means of make and break shocks from an induc- 

 tion coil. The stimulated leg responds by pronounced muscular con- 

 tractions, whereas the tied leg remains inactive. Continue the stim- 

 ulation until the muscles are fatigued. The muscular activity has 

 caused the production of lactic acid and this in turn has reacted 

 with the injected fuchsin to cause a pink or red color to develop. 

 The muscles of the inactive leg still remain unchanged in color. 



The normal color of the Fuchsin " S " when injected was red, 

 but upon being absorbed it became colorless through the action of 

 the alkalinity of the blood. Upon stimulating the muscles, how- 

 ever, as above explained, lactic acid was formed and this acid re- 

 acted with the fuchsin and again produced the original color of the 

 dye. 



II. Experiments on " Dead " Muscle. 



i. Preparation of Myosin. Take 25 grams of finely divided 

 lean beef which has been carefully washed to remove blood and 

 lymph constituents and place it in a beaker with 10 per cent sodium 

 chloride. Stir occasionally for several hours. Strain off the meat 

 pieces by means of cheese cloth, filter the solution and saturate it 

 with sodium chloride in substance. Filter off the precipitate of my- 

 osin and make the tests as given below. This filtration will pro- 

 ceed very slowly. Myosin collects as a film on the sides of the 

 filter paper and may be removed and tested before the entire volume 

 of fluid has been filtered. If this precipitate remains for any length 

 of time on the paper in contact with the air it will become trans- 

 formed into the protean myosan. Test the myosin precipitate as 

 follows : 



(a) Solubility. Try its solubility in the ordinary solvents. Is 

 myosin an albumin or a globulin? 



(b) Xanthoproteic Reaction. See page 91. 



(c) Coagulation Test. Suspend a little of the myosin in water 

 in a test-tube and heat to boiling for a few moments. Now re- 

 move the suspended material and try its solubility in 10 per cent 

 sodium chloride. What property does this experiment show myosin 

 to possess? 



Test the filtrate from the- original myosin precipitate as follows : 

 (a) Biuret Test. What does this show? 



