PRACTICAL PHYSIOLOGY 



a period of rest there is a slight increase in the ex- 

 tent of the first few succeeding contractions, the 

 second curve being a little higher than the first, 

 the third than the second, and so on (staircase phe- 

 nomenon of Bow ditch). 



Cardiac nerves. Destroy by a wire the spinal 

 cord of a frog, and also remove the cerebral hemi- 

 spheres ; this can be done without special dissec- 



AA. 



FIG. 44. FROG CARDIOGRAPH. r 



tion by cutting away the upper jaw and anterior 

 part of the skull at the level of the front of the 

 tympana (see Fig. 42). The posterior part of the 

 brain with the medulla oblongata must not be 

 injured. Fix a pair of pin electrodes passed 

 through a small cork into this part of the brain 

 and arrange for tetanization. , Lay the frog upon 

 its back on the frog-cork ; expose the heart and 

 the chief nerves which are proceeding from the 

 base of the skull to the hyoid region (vagus, glosso- 

 pharyngeal, and hypoglossal ; see Fig. 43). The var 



