﻿334 
  Dr. 
  M. 
  Foster 
  and 
  Mr. 
  A. 
  G. 
  Dew-Smith 
  on 
  the 
  [Mar. 
  18, 
  

  

  in 
  its 
  action 
  much 
  below 
  its 
  normal 
  strength), 
  simply 
  a 
  brief 
  inhibition, 
  

   indicated 
  by 
  the 
  greater 
  length 
  of 
  the 
  diastole 
  marked 
  a. 
  

  

  The 
  same 
  current, 
  allowed 
  to 
  act 
  on 
  the 
  tissue 
  a 
  sufficient 
  time 
  for 
  it 
  to 
  

   produce 
  its 
  maximum 
  effect, 
  gave 
  rise 
  to 
  a 
  making- 
  and 
  breaking-beat, 
  the 
  

   making-beat 
  being 
  what 
  we 
  have 
  called 
  kathodic 
  (starting 
  from 
  the 
  aortic 
  

   end 
  in 
  this 
  case), 
  the 
  breaking 
  anodic 
  (starting 
  from 
  the 
  auricular 
  end). 
  

   The 
  current 
  was 
  sufficiently 
  strong 
  while 
  inhibiting 
  the 
  auricular 
  end 
  to 
  

   cause 
  a 
  kathodic 
  beat 
  of 
  the 
  aortic 
  end. 
  

  

  This 
  same 
  current 
  would, 
  if 
  sufficiently 
  increased 
  in 
  strength, 
  have 
  been 
  

   able 
  to 
  produce, 
  on 
  a 
  momentary 
  passage, 
  the 
  same 
  effect 
  as 
  it 
  has 
  in 
  the 
  

   above 
  observation 
  by 
  prolonged 
  passage, 
  with 
  this 
  exception, 
  that 
  there 
  

   would 
  be 
  one 
  visible 
  beat 
  only 
  instead 
  of 
  two. 
  

  

  In 
  this 
  way, 
  by 
  simply 
  varying 
  the 
  intensity 
  of 
  the 
  current, 
  we 
  get 
  

   either 
  inhibition 
  or 
  contraction. 
  

  

  (It 
  will 
  be 
  observed 
  that 
  in 
  fig. 
  2 
  the 
  kathodic 
  beat 
  is 
  followed 
  by 
  a 
  

   pause, 
  as 
  is 
  also 
  the 
  anodic 
  beat 
  ; 
  and 
  a 
  single 
  contraction 
  produced 
  by 
  

   the 
  momentary 
  application 
  of 
  a 
  stronger 
  current 
  would 
  show 
  a 
  similar 
  

   pause. 
  These 
  pauses 
  may 
  be 
  regarded 
  as 
  partly 
  due 
  to 
  the 
  effects 
  of 
  

   the 
  contractions 
  — 
  that 
  is, 
  to 
  what 
  is 
  commonly 
  spoken 
  of 
  as 
  exhaustion 
  ; 
  

   but 
  it 
  is 
  obvious, 
  from 
  all 
  our 
  preceding 
  observations, 
  that 
  they 
  are 
  partly 
  

   due 
  to 
  the 
  direct 
  inhibitory 
  effect 
  of 
  the 
  current.) 
  

  

  There 
  is, 
  then, 
  no 
  absolute 
  contradiction 
  in 
  the 
  fact 
  of 
  a 
  current 
  pro- 
  

   ducing 
  either 
  inhibition 
  or 
  a 
  beat, 
  according 
  to 
  its 
  intensity 
  ; 
  and 
  even 
  

   when 
  a 
  beat 
  does 
  take 
  place, 
  the 
  essentially 
  depressing 
  effect 
  of 
  the 
  cur- 
  

   rent 
  is 
  seen 
  in 
  the 
  subsequent 
  pause 
  or 
  inhibition, 
  generally 
  spoken 
  of 
  as 
  

   exhaustion. 
  

  

  With 
  the 
  occurrence 
  of 
  a 
  contraction, 
  however, 
  the 
  direct 
  effects 
  of 
  the 
  

   current 
  become 
  mixed 
  with 
  the 
  effects 
  and 
  after 
  effects 
  of 
  the 
  changes 
  

   resulting 
  in 
  the 
  shortening 
  of 
  the 
  fibres 
  ; 
  and 
  thus 
  the 
  pause 
  after 
  a 
  con- 
  

   traction 
  has 
  laws 
  of 
  its 
  own, 
  more 
  or 
  less 
  different 
  from 
  those 
  of 
  the 
  

   simple 
  inhibitory 
  pause, 
  and 
  is 
  more 
  difficult 
  to 
  analyze. 
  

  

  On 
  a 
  Secondary 
  Rhythm. 
  

  

  We 
  would 
  wish 
  to 
  call 
  attention 
  to 
  the 
  peculiar 
  secondary 
  rhythm, 
  an 
  

   example 
  of 
  which 
  is 
  shown 
  in 
  fig. 
  6. 
  The 
  characters 
  of 
  the 
  rhythm 
  are 
  

   very 
  marked. 
  The 
  heart, 
  after 
  remaining 
  for 
  some 
  seconds 
  in 
  an 
  appa- 
  

   rently 
  perfectly 
  quiescent 
  state, 
  gives 
  a 
  beat 
  hardly 
  recognizable 
  even 
  

   under 
  the 
  microscope. 
  This 
  is 
  succeeded 
  by 
  feeble 
  beats, 
  which, 
  though 
  

   not 
  with 
  complete 
  regularity, 
  increase 
  in 
  force, 
  with 
  shortening 
  intervals, 
  

   until 
  a 
  maximum 
  is 
  reached, 
  after 
  which 
  the 
  beats 
  decrease 
  in 
  force, 
  

   and 
  the 
  intervals 
  lengthen, 
  until 
  perfect 
  quiescence 
  is 
  again 
  reached. 
  

  

  A 
  somewhat 
  similar 
  secondary 
  rhythm 
  has 
  been 
  observed 
  in 
  the 
  verte- 
  

   brate 
  heart 
  as 
  the 
  result 
  of 
  prolonged 
  stimulation 
  of 
  the 
  pneumogastric 
  

   nerve 
  (compare 
  Luciani, 
  Arbeiten 
  phys. 
  Anstalt, 
  Leipzig, 
  1873, 
  vii. 
  

   Jahrgang, 
  p. 
  113). 
  We 
  have 
  noticed 
  it 
  several 
  times 
  in 
  the 
  snail's 
  heart; 
  

  

  