﻿1875.] 
  Influence 
  of 
  Electricity 
  on 
  the 
  Hearts 
  of 
  Mollusks. 
  337 
  

  

  have 
  been 
  extremely 
  interesting 
  to 
  have 
  studied 
  the 
  action 
  of 
  the 
  con- 
  

   stant 
  current. 
  

  

  General 
  Considerations. 
  

  

  The 
  beat 
  of 
  the 
  ventricle 
  of 
  the 
  snail's 
  heart 
  may, 
  we 
  venture 
  to 
  think, 
  

   be 
  regarded 
  as 
  a 
  rhythmic 
  movement 
  of 
  purely 
  protoplasmic 
  nature. 
  

  

  The 
  constituent 
  fibres, 
  if 
  fibres 
  we 
  may 
  venture 
  to 
  call 
  them, 
  are 
  not 
  

   isolated 
  like 
  the 
  fibres 
  of 
  a 
  vertebrate 
  voluntary 
  muscle, 
  but 
  physiologi- 
  

   cally 
  continuous 
  ; 
  so 
  that 
  any 
  change 
  set 
  up 
  in 
  any 
  part 
  of 
  the 
  ventricle 
  

   can 
  be 
  propagated 
  over 
  the 
  whole 
  of 
  it 
  in 
  the 
  same 
  way 
  that 
  a 
  con- 
  

   traction-wave 
  set 
  going 
  at 
  any 
  point 
  in 
  a 
  striated 
  fibre 
  is 
  propagated 
  

   along 
  the 
  whole 
  length 
  of 
  the 
  fibre, 
  or 
  that 
  a 
  contraction-wave 
  is 
  propa- 
  

   gated 
  from 
  the 
  point 
  of 
  stimulation 
  along 
  a 
  nerveless 
  ureter. 
  (Compare 
  

   Engelmann, 
  Pfliiger's 
  Archiv, 
  ii. 
  p. 
  243.) 
  

  

  [The 
  ease 
  with 
  which 
  the 
  entire 
  ventricle 
  of 
  the 
  snail 
  can 
  be 
  completely 
  

   polarized 
  by 
  the 
  constant 
  current 
  may 
  be 
  regarded 
  as 
  another 
  proof 
  of 
  

   the 
  physiological 
  continuity 
  of 
  its 
  tissue. 
  The 
  want 
  of 
  conformity 
  be- 
  

   tween 
  the 
  directions 
  of 
  its 
  fibres 
  and 
  those 
  of 
  the 
  paths 
  naturally 
  taken 
  by 
  

   the 
  current 
  in 
  passing 
  from 
  one 
  electrode 
  to 
  the 
  other, 
  forbids 
  us 
  to 
  sup- 
  

   pose 
  that 
  the 
  effects 
  , 
  described 
  above 
  can 
  be 
  the 
  combined 
  result 
  of 
  a 
  

   number 
  of 
  independently 
  polarized 
  fibres.] 
  

  

  The 
  changes 
  which 
  result 
  in 
  the 
  rhythmic 
  beat 
  take 
  place 
  normally 
  in 
  

   all 
  parts 
  of 
  the 
  tissue, 
  so 
  that 
  any 
  moiety 
  of 
  the 
  ventricle 
  isolated 
  from 
  

   the 
  rest 
  is, 
  under 
  satisfactory 
  nutritive 
  conditions, 
  able 
  to 
  execute 
  rhyth- 
  

   mic 
  movements. 
  (The 
  isolation 
  may 
  be 
  mechanical, 
  as 
  by 
  section, 
  or 
  phy- 
  

   sical, 
  as 
  by 
  polarization 
  with 
  the 
  constant 
  current.) 
  

  

  "When 
  the 
  ventricle 
  is 
  cut 
  in 
  half, 
  the 
  two 
  halves 
  do 
  not 
  necessarily 
  

   beat 
  synchronously. 
  Each 
  half 
  has 
  a 
  rhythm 
  of 
  its 
  own, 
  which 
  may 
  or 
  

   may 
  not 
  be 
  (and 
  in 
  nearly 
  every 
  instance 
  is 
  not) 
  the 
  same 
  in 
  both 
  halves. 
  

   But 
  the 
  rirythru 
  of 
  each 
  half 
  is, 
  under 
  favourable 
  circumstances, 
  perfect 
  

   and 
  complete 
  ; 
  and 
  the 
  same 
  may 
  be 
  said 
  of 
  still 
  smaller 
  pieces. 
  

  

  Now 
  the 
  normal 
  beat 
  of 
  the 
  entire 
  ventricle 
  is 
  a 
  complicated 
  act. 
  

   There 
  are 
  in 
  it 
  definite 
  sequences. 
  Certain 
  fibres 
  or 
  certain 
  parts 
  of 
  the 
  

   tissue 
  begin 
  to 
  contract 
  before 
  others, 
  and 
  certain 
  parts 
  continue 
  to 
  con- 
  

   tract 
  after 
  others 
  have 
  ceased 
  to 
  do 
  so. 
  The 
  beat 
  is 
  not 
  a 
  simple 
  con- 
  

   traction-wave 
  passing 
  uniformly 
  from 
  one 
  end 
  to 
  the 
  other, 
  or 
  radiating 
  

   equally 
  in 
  all 
  directions 
  from 
  one 
  point, 
  but 
  a 
  peculiar 
  movement, 
  having 
  

   for 
  its 
  object 
  the 
  ejection 
  of 
  fluid 
  from 
  the 
  cavity 
  in 
  the 
  best 
  possible 
  

   manner, 
  and 
  is 
  hence 
  a 
  coordinated 
  movement. 
  

  

  The 
  aortic 
  half 
  of 
  the 
  ventricle, 
  separated 
  from 
  the 
  auricular 
  half, 
  

   starts 
  each 
  of 
  its 
  beats 
  quite 
  independently 
  of 
  what 
  is 
  going 
  on 
  in 
  the 
  

   ventricular 
  half, 
  and 
  vice 
  versa. 
  "When 
  the 
  two 
  are 
  physologically 
  con- 
  

   tinuous, 
  the 
  changes 
  in 
  the 
  one 
  are 
  determined 
  by 
  the 
  changes 
  in 
  the 
  

   other. 
  In 
  order 
  that 
  a 
  normal 
  beat 
  may 
  be 
  fairly 
  carried 
  through, 
  the 
  

   auricular 
  half 
  must 
  not 
  start 
  its 
  contraction 
  until 
  the 
  aortic 
  half 
  is 
  ready 
  to 
  

  

  