16 EXPERIMENTAL PHYSIOLOGY 



CHAPTER II 



PKEPARATION OF A FROG'S MUSCLE. ITS RESPONSE TO 

 STIMULATION. THE GRAPHIC METHOD 



PITH A FROG. — Pass your nail along the back of a frog's skull 

 until the groove between the skull and the first vertebra is felt, and 

 then insert the point of a fine scalpel between these two, and so divide 

 the central nervous system transversely at about the level of the 

 medulla. Now insert a blunt-pointed seeker into this aperture and 

 pass it forward into the skull cavity, so as to destroy the brain, and 

 then downwards into the vertebral canal, and thus destroy the spinal 

 cord. 



MAKE A NERVE MUSCLE PREPARATION.— The simplest and 

 one of the most convenient muscles to isolate for experiments is the 

 gastrocnemius. Its ana/tomical relations are shown in figs. 22 and 23. 

 To prepare it together with its nerve, pith a frog, and cutting through 

 the spinal column one vertebra above the sacrum, remove all the 

 soft parts in front down to the pubis, including the viscera, taking 

 care not to injure the branches of the sciatic plexus lying on the pos- 

 terior wall of the abdominal cavity. If the sacrum be now firmly held, 

 the skin over the back of the iliac bones can be drawn down, and the 

 whole of it drawn off the two legs, thus laying bare the muscles of the 

 thigh and leg. The tendo Achillis is cut across below the ankle-joint, 

 and with its sesamoid bone dissected free up to the belly of the 

 gastrocnemius, which is then isolated from the tibia and fibula right 

 up to its insertion into the femur. The head of the tibia is then cut 

 through just below the knee-joint. Next proceed to isolate the sciatic, 

 which will be found lying between the biceps, b, fig. 23, and semi- 

 membranosus, km, on the posterior surface of the thigh. Carefully 

 separate these muscles, and follow up the nerve to the pelvis, cutting 

 through its branches as they are laid bare. The nerve should not be 

 touched with metal instruments, and in its separation should not be 

 allowed to be covered with blood from the vessels which accompany 

 it. Next cut through the muscles attached to the urostyle, and divide 



