It  is  possible  by  repeated  stimuli  to  hurry  the  beat  of  a  frog's
heart,  but  not  to  fuse  two  or  more  beats  into  a  single  longer
uninterrupted  contraction.  And  as  regards  the  normal  beat
of  the  heart,  experiments  as  to  secondary  tetanus  prove  the
same  thing.  If  the  heart  of  an  anaesthetized  dog  or  other
mammal  be  carefully  laid  bare  and  the  nerve  of  a  nerve-
muscle  preparation  be  laid  on  it,  we  get  for  each  beat  a  single
twitch  of  the  signal  muscle,  and  not  a  short  tetanus  lasting
as  long  as  the  ventricular  contraction,  such  as  must  arise
were  this  contraction  tetanic.
