THE CIRCULATION OF THE BLOOD 531 



Eepeat this minimal stimulus every 5 seconds, 

 recording the contractions on a drum turned 

 about 5 mm. by hand after each contraction. 



The contractions of the ventricle will be suc- 

 cessively stronger, so that the apices of the curves 

 will form an ascending line (" staircase "). The 

 form of the staircase is always an hyperbola. 

 Successively stronger responses to repeated stim- 

 uli of uniform strength can also be obtained 

 from the curarized gastrocnemius of the frog, 

 perfused with blood, and from mammalian and 

 invertebrate muscles. The contraction appears to 

 increase the irritability. Thus the same stimu- 

 lus causes a greater contraction after a brief 

 tetanus than before. Rossbach and Bohr have 

 observed this after-effect continuing more than 

 thirty minutes. 



The Isolated Apex ; Bernstein's Experiment. 

 Draw a ligature about the ventricle halfway be- 

 tween base and apex tightly enough to crush the 

 tissues without wholly separating them. The 

 anatomical continuity between the two halves 

 of the ventricle will thereby be maintained, but 

 the physiological continuity will be lost. Release 

 the ligature. 



The isolated "apex" as a rule does not con- 

 tract. The exceptions can probably be explained 



