﻿1875.] 
  Influence 
  of 
  Electricity 
  on 
  the 
  Hearts 
  of 
  Mollusks. 
  323 
  

  

  The 
  " 
  slight 
  quiver 
  " 
  recorded 
  in 
  the 
  above 
  observations 
  does 
  not 
  

   really 
  contradict 
  the 
  statement 
  made 
  above 
  concerning 
  the 
  rapid 
  transi- 
  

   tion 
  from 
  a 
  state 
  of 
  rest 
  to 
  a 
  full 
  though 
  slight 
  beat. 
  The 
  transition 
  

   from 
  this 
  quiver 
  to 
  a 
  beat 
  is 
  quite 
  as 
  abrupt 
  as 
  that 
  from 
  a 
  state 
  of 
  com- 
  

   plete 
  rest. 
  

  

  As 
  far 
  as 
  we 
  have 
  seen, 
  inhibition 
  may 
  be 
  brought 
  about 
  whether 
  the 
  

   electrodes 
  be 
  placed 
  lengthwise 
  (one 
  at 
  the 
  auricle 
  and 
  the 
  other 
  at 
  the 
  

   aorta) 
  or 
  sideways, 
  or 
  obliquely. 
  

  

  We 
  have 
  not, 
  however, 
  paid 
  particular 
  attention 
  to 
  the 
  question, 
  

   whether 
  inhibition 
  can 
  be 
  produced 
  more 
  easily 
  in 
  one 
  direction 
  than 
  

   another 
  ; 
  nor 
  did 
  we, 
  in 
  making 
  the 
  above 
  observations, 
  pay 
  attention 
  to 
  

   the 
  direction 
  of 
  the 
  current. 
  

  

  It 
  would 
  seem, 
  then, 
  from 
  the 
  facts 
  we 
  have 
  recorded, 
  that 
  the 
  inhibi- 
  

   tion 
  produced 
  by 
  the 
  tetanizing 
  current, 
  applied 
  directly 
  to 
  the 
  ventricle 
  

   of 
  the 
  snail's 
  heart, 
  is 
  in 
  reality 
  the 
  simple 
  summation 
  of 
  the 
  effects 
  of 
  

   the 
  single 
  induction-shocks 
  which 
  make 
  up 
  the 
  tetanizing 
  current. 
  

  

  The 
  effect 
  of 
  each 
  shock 
  is 
  very 
  slight, 
  and 
  a 
  single 
  shock 
  has 
  rarely 
  

   the 
  power 
  to 
  cause 
  a 
  marked 
  prolongation 
  of 
  the 
  diastole 
  ; 
  nevertheless 
  

   there 
  is 
  an 
  effect 
  which 
  lasts 
  for 
  some 
  time 
  longer 
  than 
  the 
  application 
  

   of 
  the 
  shock 
  itself, 
  and 
  of 
  such 
  a 
  kind 
  that 
  a 
  second 
  shock 
  being 
  brought 
  

   to 
  bear 
  on 
  the 
  heart 
  before 
  the 
  effect 
  of 
  the 
  first 
  has 
  passed 
  away, 
  has 
  a 
  

   cumulative 
  effect, 
  and, 
  in 
  consequence, 
  distinct 
  inhibition 
  is 
  observed, 
  if 
  

   not 
  always 
  with 
  two, 
  at 
  least 
  with 
  several 
  shocks 
  rapidly 
  repeated. 
  

  

  Moreover 
  this 
  inhibitory 
  effect, 
  this 
  prevention 
  of 
  the 
  contraction 
  or 
  

   beat, 
  increases 
  with 
  the 
  strength 
  of 
  the 
  current 
  employed 
  up 
  to 
  a 
  certain 
  

   limit, 
  and 
  then 
  the 
  action 
  of 
  the 
  stimulus 
  is 
  suddenly 
  reversed, 
  and 
  a 
  

   contraction 
  or 
  beat 
  is 
  caused 
  instead 
  of 
  prevented. 
  

  

  There 
  seems 
  to 
  us 
  to 
  be 
  no 
  escape 
  from 
  this 
  conclusion, 
  that 
  the 
  action 
  

   of 
  the 
  induction-shock 
  on 
  the 
  tissue 
  of 
  the 
  heart 
  is 
  of 
  such 
  a 
  kind 
  that, 
  

   beginning 
  with 
  a 
  certain 
  effect 
  (inhibition), 
  as 
  it 
  increases 
  in 
  intensity 
  it 
  

   suddenly 
  topples 
  over, 
  so 
  to 
  speak, 
  and 
  produces 
  the 
  directly 
  opposite 
  

   effect 
  (contraction). 
  

  

  We 
  cannot 
  be 
  assisted 
  here 
  by 
  the 
  favourite 
  theory 
  of 
  a 
  double 
  me- 
  

   chanism 
  of 
  inhibition 
  and 
  contraction, 
  with 
  different 
  exhaustibilities, 
  

   even 
  if 
  we 
  suppose 
  that 
  these 
  mechanisms 
  are 
  evenly 
  distributed 
  all 
  over 
  

   the 
  ventricle. 
  All 
  exhaustion 
  is, 
  as 
  far 
  as 
  we 
  know, 
  gradual. 
  If 
  we 
  

   suppose 
  the 
  inhibitory 
  mechanism 
  to 
  be 
  more 
  easily 
  excited 
  and 
  ex- 
  

   hausted 
  than 
  the 
  contractile, 
  then 
  in 
  passing 
  from 
  weaker 
  to 
  stronger 
  

   stimuli 
  we 
  must 
  pass 
  through 
  a 
  phase 
  in 
  which 
  the 
  waning 
  inhibition 
  is 
  

   just 
  sufficient 
  to 
  counteract 
  the 
  increasing 
  contraction, 
  when, 
  con- 
  

   sequently, 
  no 
  effect 
  at 
  all 
  will 
  be 
  produced. 
  In 
  our 
  results, 
  on 
  the 
  con- 
  

   trary, 
  we 
  pass 
  at 
  once 
  from 
  the 
  maximum 
  of 
  inhibition 
  to 
  contraction. 
  

  

  The 
  Effects 
  of 
  the 
  Constant 
  Current. 
  

   Non-polarizable 
  electrodes 
  (a 
  modification 
  of 
  Donder's 
  pattern) 
  were 
  

  

  