24 PRACTICAL PHYSIOLOGY 



kidneys are now exposed from the back; they are 

 continuous with the sciatic nerve. To completely 

 isolate this nerve along its whole length sever the 

 attachment of the ilium to the sacrum. Split the 

 end of the spinal column longitudinally, and, hold- 

 ing one-half with forceps, lift it and the nerves 

 issuing from it up, and then gradually dissect the 

 nerves from above down by snipping their lateral 

 branches wth scissors (without touching the main 

 nerve) until the knee is nearly reached. Notice that 

 as each branch is snipped the muscles which it sup- 

 plies contract. Lay the sciatic nerve thus isolated 

 upon the gastrocnemius muscle. Lastly, cut 

 through the middle of the femur, after clearing the 

 muscles away from its lower end ; you now have a 

 nerve-muscle preparation. Place a piece of blotting 

 paper wetted with normal salt solution 1 or Ringer's 

 solution on the frog-plate, and the preparation 

 upon this, laying the nerve out upon the wet blot- 

 ting paper. Fix a pair of electrodes so that the 

 nerve lies across them. Perform the following 

 experiments, which are, for the most part, similar 

 to those already performed upon the tongue : 



i. Determine that making or breaking the circuit 

 of a constant battery is a stimulus to the nerve, 

 whereas the passage of the current usually 2 pro- 

 duces no obvious effect. 



1 Normal salt solution is made by dissolving six grammes of com- 

 mon salt in a litre of tap-water. Ringer's solution is an improved salt 

 solution made by saturating one litre of the above with calcium 

 phosphate and adding ten milligrammes of potassium chloride. 



2 For exceptions see Chapter VII. 



