ELEMENTARY EXPERIMENTAL PHYSIOLOGY 39 



to the electrodes by applying them to the tip of the tongue. If no 

 current can be detected 



(a) See that wires are not broken. 



(6) See that all metallic contacts are bright and close. 



(c) See that no short circuits are present. 



(3) Arrange the driving cord of the drum to give a fairly rapid 

 speed. (Spindles Large to Middle.) 



If two students are working together it is convenient to introduce 

 two strikers under the drum in a straight line with one another, so that 

 each revolution of the drum will give two stimulations of the muscle. 



B. Muscle-nerve Preparation. 



When everything is ready, and not before, make a nerve-muscle 

 preparation. 



(1) Kill, decapitate, and pith a frog (p. 31). Then remove the 

 anterior part by three cuts (Fig. 29), taking care that the third cut 

 leaves a piece of the vertebral column connected with the iliac 

 bones. Either skin the hind legs (Fig. 29) or place the frog 



FIG. 29. Incisions for Separation of Hind Legs. 



belly downwards on a frog-board, and divide the skin at the 

 ankle by a circular incision ; expose the tendo-Achillis and pass 

 a thread under the tendon and tie it just above the sesamoid 

 bone. In this way a ligature is attached to the muscle without 



FIG. 30. 



Muscles of the frog's leg. 



FIG. 31. 



(After Ecker.) 



FIG. 30. Dorsal aspect. 



1. Triceps femoris. 



2. Biceps femoris. 



3. Rectus interims. 



4. Semi-membranosus. 



5. Gastrocnemius. 



6. Tendo-Achillis. 



FIG. 31. Ventral aspect. 



1. Rectus internus. 6. Adductor brevis. 



2. Gracilis. 



3. Adductor longus. 



4. Vastus internus. 



5. Sartorius. 



7. Adductor magnus. 



8. Gastrocnemius. 



9. Tendo-Achillis. 



damage to or irritation of its fibres. The tendon is divided below 

 the sesamoid bone, and a pull upwards towards the knee frees the 

 gastrocnemius muscle and the skin from the remaining structures of 



