SUGGESTIONS FOR LABORATORY WORK 595 



muscle gives a vigorous contraction upon stimulation. Bring 

 around the muscle a beaker of ice-cold Ringer's solution (NaCl 

 0.7%; CaCl 2 0.026%; KC1 0.03%), which has the same osmotic 

 pressure as frog's blood. 



With the drum moving at the fastest clockwork speed obtain a 

 record of a single contraction. 



Withdraw the cold solution and allow the muscle tissue to return 

 to room temperature. With the drum moving at the same rate 

 as before obtain a record of a single contraction. Now surround 

 the muscle with Ringer's solution warmed to 30 C., and obtain a 

 record of a single contraction, again with the drum at the same 

 speed as before. 



Let the drum make a complete revolution at the speed used in 

 making those records. Determine as accurately as possible the 

 time consumed. After the smoked paper has been removed meas- 

 ure its length, and calculate the speed of the drum in centimeters 

 per second. 



Varnish the tracings and mount side by side the records of con- 

 traction at the three temperatures used. 



Compute the time required at each temperature for a complete 

 contraction. 



Set the drum moving at its slowest speed. Surround the muscle 

 with Ringer's solution, and without stimulating the muscle allow 

 it to record on the drum while the solution is gradually warmed to 

 65 C. The contraction brought about by warming above 40 is 

 called heat rigor. 



THE NERVOUS SYSTEM 



Dissections of PERIPHERAL NERVES may be made according to the 

 description in Reighard and Jennings. By way of suggestion direc- 

 tions for dissecting a typical spinal nerve and a typical cranial 

 nerve are given. 



A representative spinal nerve is the great sciatic with its 

 branches. (To be dissected in the cat.) 



Cut through the skin on the outer side of the hind leg from the 

 heel to the middle of the back. Remove the biceps femoris muscle. 

 The nerve trunk thus exposed is the sciatic. Follow the nerve 

 trunk upward, cutting away overlying tissues where necessary. 



