﻿1875.] 
  Influence 
  of 
  Electricity 
  on 
  the 
  Hearts 
  of 
  Mollusks. 
  319 
  

  

  Our 
  reasons 
  for 
  always 
  removing 
  the 
  heart 
  from 
  the 
  body 
  are 
  as 
  

   follows 
  : 
  — 
  

  

  The 
  movements 
  of 
  the 
  heart 
  cannot 
  be 
  accurately 
  observed 
  in 
  situ 
  unless 
  

   the 
  overlying 
  thin 
  integument 
  is 
  divided 
  and 
  the 
  pericardial 
  chamber 
  laid 
  

   open. 
  As 
  soon 
  as 
  this 
  is 
  done 
  the 
  beats 
  are 
  seen 
  to 
  become 
  very 
  irre- 
  

   gular. 
  Every 
  movement 
  of 
  the 
  body 
  influences 
  the 
  flow 
  of 
  blood 
  to 
  and 
  

   from 
  the 
  heart, 
  and 
  every 
  marked 
  change 
  in 
  the 
  flow 
  affects 
  the 
  force 
  

   and 
  rhythm 
  of 
  the 
  beat 
  ; 
  hence 
  observations 
  like 
  those 
  we 
  are 
  about 
  to 
  

   record 
  would 
  be 
  impossible 
  with 
  the 
  heart 
  in 
  situ. 
  

  

  We 
  have 
  been 
  unable 
  to 
  find 
  any 
  nerve 
  in 
  the 
  body 
  stimulation 
  of 
  

   which 
  would 
  inhibit 
  the 
  heart 
  in 
  the 
  same 
  way 
  as 
  stimulation 
  of 
  the 
  

   pneumogastric 
  does 
  the 
  vertebrate 
  heart. 
  

  

  By 
  removal 
  of 
  the 
  heart 
  from 
  the 
  body, 
  therefore, 
  we 
  lose 
  nothing 
  

   essential. 
  

  

  A 
  graphic 
  record 
  of 
  each 
  heart-beat 
  would 
  of 
  course 
  be 
  impossible, 
  

   In 
  order 
  to 
  obtain 
  a 
  satisfactory 
  register 
  of 
  our 
  observations, 
  we 
  

   adopted 
  the 
  following 
  plan. 
  One 
  of 
  us 
  acting 
  as 
  observer, 
  and 
  watching 
  

   the 
  heart 
  through 
  a 
  microscope 
  (50 
  to 
  100 
  diameters), 
  signalled, 
  by 
  the 
  

   sudden 
  make 
  and 
  break 
  of 
  a 
  constant 
  current, 
  each 
  beat 
  of 
  ventricle 
  or 
  

   auricle, 
  or 
  of 
  both. 
  The 
  make 
  and 
  break 
  were 
  recorded 
  by 
  a 
  magnetic 
  

   marker, 
  as 
  was 
  also 
  the 
  application 
  of 
  the 
  stimulus, 
  on 
  a 
  travelling- 
  

   paper, 
  on 
  which 
  seconds 
  were 
  at 
  the 
  same 
  time 
  being 
  marked. 
  In 
  this 
  

   way 
  a 
  little 
  practice 
  enabled 
  us 
  to 
  register 
  with 
  tolerable 
  accuracy 
  the 
  

   rhythm 
  of 
  the 
  beat, 
  though 
  we 
  could 
  not, 
  of 
  course, 
  record 
  the 
  force 
  or 
  

   character 
  of 
  each 
  pulsation. 
  

  

  Most 
  of 
  our 
  observations 
  were 
  directed 
  to 
  the 
  ventricle, 
  and 
  in 
  our 
  

   remarks 
  we 
  have 
  only 
  incidentally 
  referred 
  to 
  the 
  auricle. 
  

  

  We 
  at 
  first 
  registered 
  the 
  auricular 
  beats 
  as 
  well 
  as 
  the 
  ventricular 
  ; 
  but 
  

   an 
  increasing 
  conviction 
  of 
  the 
  independence 
  (in 
  an 
  empty 
  heart) 
  of 
  the 
  

   movements 
  of 
  the 
  two 
  chambers, 
  led 
  us 
  after 
  a 
  while 
  to 
  confine 
  our 
  

   attention 
  to 
  the 
  ventricle. 
  

  

  The 
  application 
  of 
  the 
  current 
  was 
  made 
  by 
  one 
  of 
  us 
  while 
  the 
  other, 
  

   watchiug 
  and 
  recording 
  the 
  beats 
  of 
  the 
  heart, 
  was 
  unaware 
  of 
  what 
  was 
  

   being 
  done. 
  The 
  faithfulness 
  of 
  the 
  observations 
  was 
  thus 
  materially 
  

   assisted. 
  

  

  Finding 
  the 
  heart 
  of 
  the 
  common 
  snail 
  more 
  vigorous, 
  though 
  smaller, 
  

   than 
  that 
  of 
  the 
  edible 
  snail, 
  we 
  confined 
  our 
  attention 
  to 
  the 
  former. 
  

  

  The 
  snail's 
  heart 
  consists, 
  as 
  is 
  well 
  known, 
  of 
  a 
  thin-walled 
  globular 
  

   auricle, 
  separated 
  by 
  a 
  ring 
  of 
  non-contractile 
  tissue 
  from 
  an 
  oval, 
  

   almost 
  conical, 
  fleshy 
  ventricle. 
  Into 
  the 
  former, 
  opposite 
  the 
  auriculo- 
  

   ventricular 
  orifice, 
  opens 
  the 
  large 
  pulmonary 
  vein. 
  The 
  latter 
  at 
  its 
  

   apex, 
  opposite 
  the 
  auricle, 
  narrows 
  to 
  the 
  large 
  artery, 
  which 
  we 
  have 
  

   spoken 
  of 
  as 
  the 
  aorta. 
  In 
  speaking 
  of 
  the 
  ventricle 
  we 
  shall 
  frequently 
  

   have 
  occasion 
  to 
  distinguish 
  the 
  broader 
  auricular 
  end 
  next 
  to 
  the 
  auricle 
  

   from 
  the 
  narrow 
  aortic 
  end, 
  which 
  is 
  continuous 
  with 
  the 
  aorta. 
  In 
  

  

  