﻿322 
  Dr. 
  M. 
  Foster 
  and 
  Mr. 
  A. 
  G. 
  Dew-Smith 
  on 
  the 
  [Mar. 
  18, 
  

  

  We 
  have 
  said 
  that 
  single 
  induction-shocks, 
  below 
  a 
  certain 
  intensity, 
  

   produce 
  apparently 
  no 
  effect 
  on 
  the 
  heart. 
  

  

  We 
  have 
  thrown 
  in 
  single 
  shocks, 
  of 
  a 
  strength 
  too 
  slight 
  to 
  cause 
  a 
  

   beat 
  or 
  contraction, 
  at 
  all 
  phases 
  of 
  the 
  cardiac 
  cycle, 
  without 
  being 
  able 
  

   to 
  detect 
  any 
  variation 
  in 
  either 
  the 
  character 
  or 
  frequency 
  of 
  the 
  beat. 
  

   "We 
  would 
  not 
  venture 
  to 
  say 
  that 
  absolutely 
  no 
  effect 
  is 
  produced, 
  but 
  

   the 
  effect 
  is 
  not 
  manifested 
  by 
  any 
  change 
  in 
  the 
  rhythm 
  which 
  can 
  be 
  

   measured 
  on 
  our 
  recording 
  surface, 
  travelling 
  half 
  an 
  inch 
  a 
  second, 
  or 
  

   by 
  any 
  change 
  in 
  the 
  beat 
  which 
  can 
  be 
  recognized 
  by 
  the 
  eye. 
  

  

  We 
  have 
  also 
  thrown 
  in 
  single 
  shocks 
  repeated 
  at 
  the 
  same 
  phase 
  for 
  

   several 
  beats 
  in 
  succession. 
  Thus 
  we 
  have 
  thrown 
  in 
  a 
  single 
  weak 
  

   shock 
  at 
  the 
  height 
  of 
  systole 
  as 
  well 
  as 
  in 
  the 
  middle 
  of 
  diastole, 
  during 
  

   several 
  successive 
  beats, 
  without 
  detecting 
  any 
  appreciable 
  effects. 
  

  

  Very 
  marked, 
  however, 
  are 
  the 
  results 
  when 
  the 
  weak 
  single 
  induction- 
  

   shocks 
  are 
  rapidly 
  repeated, 
  sothat 
  twoor 
  more 
  shocks 
  fall 
  within 
  each 
  cycle. 
  

  

  The 
  application 
  of 
  the 
  shocks 
  produces 
  no 
  contraction 
  or 
  heat, 
  but 
  is 
  fol- 
  

   lowed 
  by 
  a 
  prolongation 
  of 
  the 
  diastole. 
  

  

  In 
  other 
  words, 
  a 
  single 
  induction-shock, 
  too 
  weak 
  to 
  produce 
  by 
  itself 
  

   any 
  effect, 
  has, 
  when 
  repeated 
  within 
  the 
  cardiac 
  cycle, 
  a 
  distinct 
  inhi- 
  

   bitory 
  action. 
  

  

  The 
  beat 
  which 
  immediately 
  follows 
  the 
  prolonged 
  diastole 
  is 
  a 
  feeble 
  one 
  

   (as 
  are 
  also 
  the 
  beats 
  which 
  occur 
  when 
  the 
  shocks 
  are 
  repeated 
  many 
  

   times 
  in 
  succession, 
  so 
  as 
  to 
  cover 
  the 
  periods 
  of 
  more 
  than 
  one 
  prolonged 
  

   diastole) 
  ; 
  but 
  the 
  inhibition 
  is 
  followed, 
  as 
  was 
  the 
  case 
  with 
  the 
  inter- 
  

   rupted 
  current, 
  by 
  a 
  stage 
  of 
  increased 
  rapidity 
  and 
  vigour 
  of 
  beat 
  — 
  that 
  

   is 
  to 
  say, 
  the 
  inhibition 
  thus 
  caused 
  has 
  all 
  the 
  characters 
  of 
  a 
  normal 
  

   inhibition. 
  

  

  Repeated 
  trials 
  have 
  shown 
  us 
  that, 
  having 
  due 
  regard 
  to 
  the 
  irrita- 
  

   bility 
  of 
  the 
  heart, 
  the 
  more 
  feeble 
  the 
  current 
  the 
  more 
  rapid 
  must 
  be 
  

   the 
  repetition 
  of 
  shocks, 
  and 
  the 
  greater 
  the 
  number 
  of 
  shocks 
  given 
  in 
  

   order 
  to 
  produce 
  inhibition. 
  

  

  As 
  an 
  instance 
  of 
  very 
  successful 
  inhibition, 
  we 
  may 
  refer 
  to 
  fig. 
  1, 
  

   (p. 
  342), 
  where 
  two 
  shocks 
  were 
  found 
  sufficient 
  to 
  produce 
  a 
  very 
  

   marked 
  prolongation 
  of 
  the 
  diastole. 
  

  

  A 
  particularly 
  interesting 
  result 
  is 
  shown 
  in 
  fig. 
  2. 
  This 
  is 
  the 
  

   only 
  case 
  in 
  which 
  we 
  succeeded 
  in 
  obtaining 
  inhibition 
  as 
  the 
  result 
  

   of 
  one 
  single 
  opening 
  shock. 
  The 
  shock, 
  however, 
  was 
  (in 
  relation 
  to 
  

   the 
  heart's 
  irritability) 
  a 
  comparatively 
  strong 
  one; 
  it 
  was 
  just 
  on 
  

   the 
  verge 
  of 
  being 
  strong 
  enough 
  to 
  produce 
  a 
  contraction. 
  Our 
  notes 
  

   record 
  that 
  at 
  the 
  moment 
  of 
  stimulation 
  (the 
  stimulus 
  being 
  thrown 
  in 
  

   very 
  soon 
  after 
  the 
  normal 
  beat) 
  " 
  a 
  slight 
  quiver, 
  quite 
  distinct 
  from 
  

   any 
  ordinary 
  contraction, 
  and 
  limited 
  to 
  the 
  neighbourhood 
  of 
  the 
  elec- 
  

   trodes, 
  was 
  observed." 
  

  

  It 
  will 
  be 
  noticed 
  that 
  after 
  the 
  first 
  two 
  shocks 
  the 
  heart 
  became 
  

   habituated 
  to 
  tbe 
  stimulus, 
  and 
  the 
  last 
  two 
  shocks 
  produced 
  no 
  effect. 
  

  

  